Dynamic coupling of fast channel gating with slow ATP-turnover underpins protein transport through the Sec translocon.

The Sec translocon is a highly conserved membrane assembly for polypeptide transport across, or into, lipid bilayers. In bacteria, secretion through the core channel complex-SecYEG in the inner membrane-is powered by the cytosolic ATPase SecA. Here, we use single-molecule fluorescence to interrogate the conformational state of SecYEG throughout the ATP hydrolysis cycle of SecA. We show that the SecYEG channel fluctuations between open and closed states are much faster (~20-fold during translocation) than ATP turnover, and that the nucleotide status of SecA modulates the rates of opening and closure. The SecY variant PrlA4, which exhibits faster transport but unaffected ATPase rates, increases the dwell time in the open state, facilitating pre-protein diffusion through the pore and thereby enhancing translocation efficiency. Thus, rapid SecYEG channel dynamics are allosterically coupled to SecA via modulation of the energy landscape, and play an integral part in protein transport. Loose coupling of ATP-turnover by SecA to the dynamic properties of SecYEG is compatible with a Brownian-rachet mechanism of translocation, rather than strict nucleotide-dependent interconversion between different static states of a power stroke.

Structural basis of SecA-mediated protein translocation.

Secretory proteins are cotranslationally or posttranslationally translocated across lipid membranes via a protein-conducting channel named SecY in prokaryotes and Sec61 in eukaryotes. The vast majority of secretory proteins in bacteria are driven through the channel posttranslationally by SecA, a highly conserved ATPase. How a polypeptide chain is moved by SecA through the SecY channel is poorly understood. Here, we report electron cryomicroscopy structures of the active SecA-SecY translocon with a polypeptide substrate. The substrate is captured in different translocation states when clamped by SecA with different nucleotides. Upon binding of an ATP analog, SecA undergoes global conformational changes to push the polypeptide substrate toward the channel in a way similar to how the RecA-like helicases translocate their nucleic acid substrates. The movements of the polypeptide substrates in the SecA-SecY translocon share a similar structural basis to those in the ribosome-SecY complex during cotranslational translocation.

How do different marine engine fuels and wet scrubbing affect gaseous air pollutants and ozone formation potential from ship emissions?

Sulphur Emission Control Areas (SECAs), mandated by the International Maritime Organization (IMO), regulate fuel sulphur content (FSC) to mitigate the environmental and health impact of shipping emissions in coastal areas. Currently, FSC is limited to 0.1% (w/w) within and 0.5% (w/w) outside SECAs, with exceptions for ships employing wet sulphur scrubbers. These scrubbers enable vessels using non-compliant fuels such as high-sulphur heavy fuel oils (HFOs) to enter SECAs. However, while sulphur reduction via scrubbers is effective, their efficiency in capturing other potentially harmful gases remains uncertain. Moreover, emerging compliant fuels like highly aromatic fuels or low-sulphur blends lack characterisation and may pose risks. Over three years, we assessed emissions from an experimental marine engine at 25% and 75% load, representative of manoeuvring and cruising, respectively. First, characterizing emissions from five different compliant and non-compliant fuels (marine gas oil MGO, hydro-treated vegetable oil HVO, high-, low- and ultra-low sulphur HFOs), we calculated emission factors (EF). Then, the wet scrubber gas-phase capture efficiency was measured using compliant and non-compliant HFOs. NOx EF varied among fuels (5200-19700 mg/kWh), with limited scrubber reduction. CO (EF 750-13700 mg/kWh) and hydrocarbons (HC; EF 122-1851 mg/kWh) showed also insufficient abatement. Carcinogenic benzene was notably higher at 25% load and about an order of magnitude higher with HFOs compared to MGO and HVO, with no observed scrubber reduction. In contrast, carbonyls such as carcinogenic formaldehyde and acetaldehyde, acting as ozone precursors, were effectively scrubbed due to their polarity and water solubility. The ozone formation potential (OFP) of all fuels was examined. Significant EF differences between fuels and engine loads were observed, with the wet scrubber providing limited or no reduction of gaseous emissions. We suggest enhanced regulations and emission abatements in the marine sector to mitigate gaseous pollutants harmful to human health and the environment.

Protein secretion zones during overexpression of amylase within the Gram-positive cell wall.

BACKGROUND: Whereas the translocation of proteins across the cell membrane has been thoroughly investigated, it is still unclear how proteins cross the cell wall in Gram-positive bacteria, which are widely used for industrial applications. We have studied the secretion of α-amylase AmyE within two different Bacillus strains, B. subtilis and B. licheniformis. RESULTS: We show that a C-terminal fusion of AmyE with the fluorescent reporter mCherry is secreted via discrete patches showing very low dynamics. These are visible at many places within the cell wall for many minutes. Expression from a high copy number plasmid was required to be able to see these structures we term "secretion zones". Zones corresponded to visualized AmyE activity on the surface of cells, showing that they release active enzymes. They overlapped with SecA signals but did not frequently co-localize with the secretion ATPase. Single particle tracking showed higher dynamics of SecA and of SecDF, involved in AmyE secretion, at the cell membrane than AmyE. These experiments suggest that SecA initially translocates AmyE molecules through the cell membrane, and then diffuses to a different translocon. Single molecule tracking of SecA suggests the existence of three distinct diffusive states of SecA, which change during AmyE overexpression, but increased AmyE secretion does not appear to overwhelm the system. CONCLUSIONS: Because secretion zones were only found during the transition to and within the stationary phase, diffusion rather than passive transport based on cell wall growth from inside to outside may release AmyE and, thus, probably secreted proteins in general. Our findings suggest active transport through the cell membrane and slow, passive transition through the cell wall, at least for overexpressed proteins, in bacteria of the genus Bacillus.

First Report of 'Candidatus Phytoplasma citri' related strain (16SrII-C subgroup) associated with phyllody disease of cumin in India.

Cumin (Cuminum cyminum L.), is an important export-oriented seed spice crop for India. Cumin is popularly used for flavouring food, including soups, pickles and vegetables, and for herbal medicine. India is the largest producer, consumer and exporter of cumin seed with an annual production of 0.795 million tones over an area of 1.09 million hectares. During 2020-21, India exported about 0.299 million tons of cumin worth of Rs 33280 million (Anonymous, 2021). Recently, phytoplasma suspected symptoms were observed in cumin at Agricultural Research Station, Mandor, Jodhpur, Rajasthan, India from 2019. The symptoms related to phytoplasma infection were first recorded after 70-75 days of sowing in the month of January of the years 2019 to 2022. The major symptoms recorded were yellowing, phyllody, witches-broom, yellowing and deformed elongated seeds. Disease incidence was recorded as 0.25-1.0%, 0.5-1.5%, 0.5-2.5 % and 0.5-10.6% during the years 2019, 2020, 2021 and 2022, respectively using quadrate method. In 2022, among different genotypes assessed GC 4, MCU 73, MCU 105, and MCU 32 exhibited lower disease incidences ranging from 0.5% to 1.5%, while MCU 78 recorded the highest disease incidence at 10.6%. To detect the association of phytoplasma with symptomatic cumin samples, genomic DNA was extracted from four representative cumin genotypes (CuPP-MND-01 to CuPP-MND-04) and one asymptomatic cumin plant using the Qiagen DNeasy plant mini kit (Germany). The extracted DNA was amplified using nested PCR assays with universal phytoplasma detection primers for 16S rRNA gene (P1/P7 and R16F2n/R16R2) (Schneider et al., 1995; Gundersen and Lee, 1996) and secA gene specific primers (SecAfor1/SecArev3 followed by nested PCR primers SecAfor5/ SecArev2) (Hodgetts et al. 2008; Bekele et al. 2011). The amplicons of ∼1.25 kb with 16S rRNA gene and ∼600 bp with secA gene specific primers were amplified in all symptomatic cumin plant samples and positive control of brinjal little leaf. PCR amplified products from the four selected positive samples (CuPP-MND-01 to CuPP-MND-04) of 16S rRNA gene and secA gene, were sequenced from both ends. The 1,245 bp sequences were deposited in GenBank (OQ299007-10), which showed 100% sequence identity with each other and 99.4% identity with 'Candidatus Phytoplasma citri' reference strain (GenBank accession: U15442) (Rodrigues Jardim et al. 2023). The phylogenetic analysis and virtual RFLP analysis using 17 restriction enzymes of 16S rRNA gene sequences through iPhyclassifier allowed affiliating the cumin phytoplasma strains with 16SrII-C subgroup strain with a similarity coefficient of 1 to the reference pattern of 16Sr group II, subgroup C (GenBank accession: AJ293216) (Zhao et al. 2009). In addition, the phylogenetic analysis of the secA gene-based sequences (OQ305073-76) further confirmed the close association of 16SrII-C group phytoplasmas with phyllody and witches' broom disease of cumin. Earlier 16SrII-C subgroup phytoplasma has been reported from various crops and weeds in India (Rao et al. 2021). However, no phytoplasma association has been reported earlier with cumin in India and abroad. To the best of our knowledge, this is the first report on the association of 16SrII-C group phytoplasma causing phyllody, witches' broom in cumin genotypes. This report has economic and epidemiological implications and needs immediate attention to reduce export losses due to phytoplasma disease in cumin and to prevent the potential spread to other crops.

Protein translocation by the SecA ATPase occurs by a power-stroke mechanism.

SecA belongs to the large class of ATPases that use the energy of ATP hydrolysis to perform mechanical work resulting in protein translocation across membranes, protein degradation, and unfolding. SecA translocates polypeptides through the SecY membrane channel during protein secretion in bacteria, but how it achieves directed peptide movement is unclear. Here, we use single-molecule FRET to derive a model that couples ATP hydrolysis-dependent conformational changes of SecA with protein translocation. Upon ATP binding, the two-helix finger of SecA moves toward the SecY channel, pushing a segment of the polypeptide into the channel. The finger retracts during ATP hydrolysis, while the clamp domain of SecA tightens around the polypeptide, preserving progress of translocation. The clamp opens after phosphate release and allows passive sliding of the polypeptide chain through the SecA-SecY complex until the next ATP binding event. This power-stroke mechanism may be used by other ATPases that move polypeptides.

Humic-like Substances (HULIS) in Ship Engine Emissions: Molecular Composition Effected by Fuel Type, Engine Mode, and Wet Scrubber Usage.

Humic-like substances (HULIS), known for their substantial impact on the atmosphere, are identified in marine diesel engine emissions obtained from five different fuels at two engine loads simulating real world scenarios as well as the application of wet sulfur scrubbers. The HULIS chemical composition is characterized by electrospray ionization (ESI) ultrahigh resolution mass spectrometry and shown to contain partially oxidized alkylated polycyclic aromatic compounds as well as partially oxidized aliphatic compounds, both including abundant nitrogen- and sulfur-containing species, and clearly different to HULIS emitted from biomass burning. Fuel properties such as sulfur content and aromaticity as well as the fuel combustion efficiency and engine mode are reflected in the observed HULIS composition. When the marine diesel engine is operated below the optimum engine settings, e.g., during maneuvering in harbors, HULIS-C emission factors are increased (262-893 mg kg-1), and a higher number of HULIS with a shift toward lower degree of oxidation and higher aromaticity is detected. Additionally, more aromatic and aliphatic CHOS compounds in HULIS were detected, especially for high-sulfur fuel combustion. The application of wet sulfur scrubbers decreased the HULIS-C emission factors by 4-49% but also led to the formation of new HULIS compounds. Overall, our results suggest the consideration of marine diesel engines as a relevant regional source of HULIS emissions.

Catheter-related bloodstream infection caused by Tsukamurella tyrosinosolvens identified by secA1sequencing in an immunocompromised child: a case report.

BACKGROUND: Tsukamurella spp. are obligate aerobic, gram-positive, non-motile, and slightly acid-fast bacilli belonging to the Actinomycetes family. They share many characteristics with Nocardia, Rhodococcus, Gordonia, and the rapidly growing Mycobacterium species. Therefore, standard testing may misidentify Tsukamurella spp. as another species. Accurate and rapid diagnosis is critical for proper infection management, but identification of this bacterium is difficult in the standard laboratory setting. CASE PRESENTATION: A bloodstream infection caused by a gram-positive bacterium and related to a central venous catheter was identified in an immunocompromised 2-year-old girl. Tsukamurella tyrosinosolvens was identified by modified secA1 sequencing. Antibiotic treatment and removal of the central venous catheter resolved the infection. Inappropriate management of the catheter during an overnight stay outside of the hospital was considered as a possible source of infection. CONCLUSIONS: SecA1 sequencing may be a useful diagnostic tool in the identification of T. tyrosinosolvens. Providing proper central venous catheter care instructions to patients, their families, and medical staff is important for infection prevention.

Refined measurement of SecA-driven protein secretion reveals that translocation is indirectly coupled to ATP turnover.

The universally conserved Sec system is the primary method cells utilize to transport proteins across membranes. Until recently, measuring the activity-a prerequisite for understanding how biological systems work-has been limited to discontinuous protein transport assays with poor time resolution or reported by large, nonnatural tags that perturb the process. The development of an assay based on a split superbright luciferase (NanoLuc) changed this. Here, we exploit this technology to unpick the steps that constitute posttranslational protein transport in bacteria. Under the conditions deployed, the transport of a model preprotein substrate (proSpy) occurs at 200 amino acids (aa) per minute, with SecA able to dissociate and rebind during transport. Prior to that, there is no evidence for a distinct, rate-limiting initiation event. Kinetic modeling suggests that SecA-driven transport activity is best described by a series of large (∼30 aa) steps, each coupled to hundreds of ATP hydrolysis events. The features we describe are consistent with a nondeterministic motor mechanism, such as a Brownian ratchet.

First report of a 'Candidatus Phytoplasma aurantifolia'-related strain associated with faba bean phyllody symptoms in India.

Vicia faba L. commonly known as broad bean or faba bean is one of the most widely grown protein rich legume crops. Out of more than 50 faba bean-producing countries, about 90% production is concentrated in the Asian, European Union (EU), and African region (FAO, 2020). Owing to its high nutritional value, both the fresh pods and dry seeds are consumed. During March 2022, some plants with little leaf and phyllody symptoms such as leaf-like floral structures were observed in the experimental fields of Indian Agricultural Research Institute (IARI), New Delhi (Fig. 1 a, b, c). The twig samples were collected from two individual symptomatic and one from asymptomatic plant. DNA was extracted using CTAB (cetyl trimethyl ammonium bromide) method (Ahrens and Seemüller, 1992; Marzachi et al. 1998) and examined for the association of phytoplasma through nested PCR using the universal primers P1/P7 and R16F2n/R16R2 targeting the 16SrRNA gene (Deng and Hiruki 1991; Gundersen and Lee 1996) and the other set of primers secAfor1/secArev3 and secAfor2/secArev3 targeting secA gene (Hodgetts et al. 2008). The DNA from symptomatic plants resulted the amplicons of 1200bp and 840bp specific to 16S rRNA and secA gene respectively. The gel purified PCR products were cloned into pGEM®-T Easy Vector system (Promega) and outsourced for Sanger sequencing at Agri Genome Labs, Kerala, India. The resultant 16S rRNA sequences (GenBank Acc. No. OP978231, OP978232) and secA sequences (ON715392 and ON715393) were examined through NCBI BLASTn analysis. The 16S rRNA sequences of the V. faba strains shared a minimum of 99.85% similarity with the phytoplasma strain causing little leaf and phyllody disease of sesame in India (MW622017) and a maximum of 100% sequence identity with the Vigna radiata phyllody and necrosis phytoplasma strain of Jodhpur (OP935760) India, whereas the secA gene sequences showed 100% identity with Tephrosia purpurea witches'-broom phytoplasma (MW603929) from China and a minimum of 91.14% similarity with 'Candidatus Phytoplasma aurantifolia' (MW020541) from India. The pairwise comparison results were completely in support of the corresponding phylogenetic sequence analysis results of 16SrRNA and secA gene sequences of faba bean strains in comparison with other strains retrieved from GenBank database, wherein the faba bean strains got clustered with 16SrII-D subgroup related strains (Fig. 2 a and b). Virtual RFLP analysis through iPhyClassifer tool through in silico digestion of R16F2n/R2 region of 16S rRNA gene of the faba bean strain using 17 restriction endonuclease enzymes resulted in the RFLP profiles similar to that of the profile of phytoplasma subgroup 16SrII-D (Y10097: papaya yellow crinkle) used as reference strain with a similarity coefficient value of 1.0. All the results of this investigation confirmed the association of 'Candidatus phytoplasma aurantifolia' (16SrII-D) with the diseased faba bean plants in this study. Previous reports of phytoplasma infecting faba bean include a group 16SrIII strain detected in Spain in 2004 (Castro and Romero), a subgroup 16SrII-D strain detected in Sudan in 2012 (Alfaro-Fernandez et al.), a group 16SrII strain detected in Saudi Arabia in 2014 (Al-Saleh and Amer), and subgroup 16SrIII-J strains detected in Egypt in 2014 (Hamed et al.) and in Peru in 2021 (Torres-Suarez et al.). To the best of our knowledge, these findings, document the first report of the association of 'Candidatus Phytoplasma aurantifolia' (subgroup 16SrII-D) with faba bean plants in India. This report necessitates further research on the status of distribution of this phytoplasma strain in other locations and hosts in the country so as to develop possible strategies to contain its further spread and management of the disease.

Protease protection assays show polypeptide movement into the SecY channel by power strokes of the SecA ATPase.

Bacterial secretory proteins are translocated post-translationally by the SecA ATPase through the protein-conducting SecY channel in the plasma membrane. During the ATP hydrolysis cycle, SecA undergoes large conformational changes of its two-helix finger and clamp domains, but how these changes result in polypeptide movement is unclear. Here, we use a reconstituted purified system and protease protection assays to show that ATP binding to SecA results in a segment of the translocation substrate being pushed into the channel. This motion is prevented by mutation of conserved residues at the finger's tip. Mutation of SecA's clamp causes backsliding of the substrate in the ATP-bound state. Together, these data support a power stroke model of translocation in which, upon ATP binding, the two-helix finger pushes the substrate into the channel, where it is held by the clamp until nucleotide hydrolysis has occurred.

First report of association of 'Candidatus Phytoplasma asteris' with Moringa oleifera leaf yellowing and stunting disease in India.

Moringa oleifera (family Moringaceae) also known as the 'drumstick tree' is a significant nutritious and medicinal plant that is commonly grown in India and contains a variety of vital phytochemicals. M. oleifera is used in several Indian herbal medicine formulations to treat a variety of illnesses (Kumar and Rao 2021). Typical phytoplasma symptoms of leaf yellowing and stunting were observed in M. oleifera trees up to 10% incidence at Acharya Narendra Dev University of Agriculture & Technology, Ayodhya, Uttar Pradesh, India in November 2021 and stunting with less fruit bearings symptoms with 8% incidence in October 2021 at Jonnalakothapalle village of Mudigubba mandal of Ananthapuramu district in Andhra Pradesh, India (Fig.1a, b). To investigate the possibility of a phytoplasma association with the symptoms, total DNA was isolated from the leaf samples collected from two diseased and two healthy plants from both the locations using CTAB method. The DNAs isolated were analysed by nested polymerase chain reaction (PCR) with universal phytoplasma primer pairs P1/P7 and R16F2n/R16R2 for the 16S rRNA gene (Deng and Hiruki 1991; Gundersen and Lee 1996) and secAfor1/sArev3 and SecAfor2/ SecArev3 for secA gene (Hodgetts et al. 2008). Amplicons of the expected size (~1.25kb from 16S rRNA gene and ~480bp from secA gene) were obtained from symptomatic plants only. The nested PCR products were cloned (pGEM-T Easy Vector, Promega), sequenced (ABA Biotech, India) and the sequences were deposited in GenBank with accession numbers OP358449, OP358450, OP358451, OP358452 for the 16SrRNA gene (~1.25 kb) and OP358443, OP358444, OP358445, OP358446 for the secA gene (~480 bp). BLASTn analysis revealed that the partial 16S rRNA gene sequences of M. oleifera phytoplasma isolate shared up to 99.9% sequence identity with the strain 'Candidatus Phytoplasma asteris' (Accession numbers MN909051, MN909047) and secA gene sequences shared up to 100% sequence identity with 'Ca. Phytoplasma asteris' (Accession numbers KJ434315, KJ462009) belonging to 16SrI group. The 16S rRNA and secA genes sequence-based phylogenetic analysis (Figure 1d,e) showed that the phytoplasma strain associated with M. oleifera leaf yellowing and stunting clustered within the 16SrI phytoplasma group closest to 16SrI-B ('Ca. P. asteris') subgroup strains. Furthermore, the virtual RFLP pattern derived from the query 16S rDNA F2nR2 fragment is identical (similarity coefficient 1.00) to the reference pattern of 16Sr group I, subgroup B (GenBank accession: AP006628). To the best of our knowledge, this is the first report of the 16SrI-B subgroup of the phytoplasma strains with M. oleifera in the world. 'Candidatus Phytoplasma asteris' (16SrI-B subgroup) strains have been reported from several other commercial crops and weed hosts in India and efficient leafhopper vectors have been identified (Rao 2021; Reddy 2021). This indicates that the 'Ca. P. asteris'-related strains (16SrI-B) are widespread and infecting several plant species in India. The increasing incidence of the 16SrI-B strain and its wide host range in India strongly suggests further research into the epidemiology involved in the dynamic spread of the disease in order to recommend a suitable management approach.

SecA2 Associates with Translating Ribosomes and Contributes to the Secretion of Potent IFN-ß Inducing RNAs.

Protein secretion plays a central role in modulating interactions of the human pathogen Listeria monocytogenes with its environment. Recently, secretion of RNA has emerged as an important strategy used by the pathogen to manipulate the host cell response to its advantage. In general, the Sec-dependent translocation pathway is a major route for protein secretion in L. monocytogenes, but mechanistic insights into the secretion of RNA by these pathways are lacking. Apart from the classical SecA1 secretion pathway, L. monocytogenes also encodes for a SecA paralogue (SecA2) which targets the export of a specific subset of proteins, some of which are involved in virulence. Here, we demonstrated that SecA2 co-sediments with translating ribosomes and provided evidence that it associates with a subset of secreted small non-coding RNAs (sRNAs) that induce high levels of IFN-ß response in host cells. We found that enolase, which is translocated by a SecA2-dependent mechanism, binds to several sRNAs, suggesting a pathway by which sRNAs are targeted to the supernatant of L. monocytogenes.

First report of Candidatus Phytoplasma cynodontis (16SrXIV-A subgroup) associated with cauliflower phyllody and flat stem in India.

Symptoms of suspected phytoplasma infection were observed in cauliflower (Brassica oleracea var. botrytis) (cultivar NS60N) at Integrated Farming System Research Station, Trivandrum, Kerala, India (08o28'28"N, 76o57'47"E) in April-2021. The disease incidence was recorded up to 10% in different fields. The disease manifested as stunting, phyllody, floral malformation and flattening of stem (Fig.1A,B). Ten symptomatic and five asymptomatic plants were assayed for the presence of phytoplasma using nested PCR assays performed with P1/P7 and R16F2n/R16R2 primer pairs for 16S rRNA gene and SecAfor1/ SecArev3 and SecAfor2/ SecArev3 for secA gene (Deng and Hiruki 1991; Gundersen and Lee 1996; Hodgetts et al. 2008). The expected amplicons of ~1.25 kb and ~480 bp were consistently amplified in all the symptomatic cauliflower samples with the phytoplasma specific universal 16S rRNA and secA gene specific primers. Nested PCR products (~1.2 kb and 480 bp) amplified from cauliflower was cloned in EcoRI restriction sites of pGEM-T Easy vector (Promega, USA). The cloned nested PCR products were directly sequenced (16S rRNA gene: Acc. Nos. MZ196223, MZ196224; secA gene: MZ215721, MZ215722) in both forward and reverse directions which showed 99.77% sequence identity with Candidatus Phytoplasma cynodontis reference strain (Acc. No. AJ550984). Further analyses of the 16S rRNA and secA genes based phylogenetic tree (Fig. 2A and B) and the iPhyClassifier-based virtual RFLP analysis of 16Sr RNA gene study demonstrated that the phytoplasma-associated with cauliflower phyllody & flat stem disease (CaPP) belonged to 16SrXIV-A subgroup with a similarity coefficient of 1.0. No amplicon was observed from any of the asymptomatic cauliflower plants with the specific tested primers of both the genes. Earlier association of 16SrXV-A subgroup (Candidatus Phytoplasma brasiliense) and 16Sr III-J subgroup in Brazil (Canale and Badendo, 2013; Rappussi et al. 2012), 16SrII-A (Candidatus Phytoplasma aurantifolia) subgroup in China (Cai et al. 2016) and 16SrVI-A (Candidatus Phytoplasma trifolii) subgroup in Iran (Salehi 2007) were reported in cauliflower. Another species of cabbage, Brassica oleracea var. capitata L. was reported as host of Ca. P. trifloii (16Sr VI-D subgroup) from north India (Gopala et al. 2018). To our knowledge, this is the first report of a 'Candidatus Phytoplasma cynodontis', 16SrXIV-A subgroup related phytoplasma strain associated with cauliflower phyllody and flat stem in the world. The results described in this report confirm that the 16SrXIV-A phytoplasma, a widely distributed strain associated with sugarcane, wheat, grasses, sapota and many ornamentals in India (Rao 2021), has also infected cauliflower. This is not only the first instance of cauliflower phyllody disease found in India, but also the first instance of CaPP disease caused by 16SrXIV-A subgroup phytoplasma worldwide. This report has epidemiological significance and needs immediate attention, as cauliflower is the one of the most common vegetable crop grown all over India.

Container fleet renewal considering multiple sulfur reduction technologies and uncertain markets amidst COVID-19.

The onset of 2020 is marked by stricter restrictions on maritime sulfur emissions and the spread of Coronavirus Disease 2019 (COVID-19). In this background, liner companies now face the challenge to find suitable sulfur reduction technologies, make reasonable decisions on fleet renewal, and prepare stable operation plans under the highly uncertain shipping market. Considering three sulfur reduction technologies, namely, fuel-switching, scrubber, and liquefied natural gas (LNG) dual-fuel engine, this paper develops a robust optimization model based on two-stage stochastic linear programming (SLP) to formulate a decision plan for container fleet, which can deal with various uncertainties in future: freight demand, ship charter rate, fuel price, retrofit time and Sulfur Emission Control Area (SECA) ratio. The main decision contents include ship acquisition, ship retrofit, ship sale, ship charter, route assignment, and speed optimization. The effectiveness of our plan was verified through a case study on two liner routes from the Far East to Northwest America, operated by COSCO Shipping Lines. The results from SLP model show that large-capacity fuel-switching ships and their LNG dual-fuel engine retrofits should be included in the long-term investment and operation plan; slow-steaming is an important operational decision for ocean liner shipping; if the current SECA boundary is not further expanded or the sulfur emission restrictions not further tightened, the scrubber ship will have no advantage in investment cost and operation. However, considering the probabilities of more flexible scenarios, the results from the robust model suggest that it is beneficial to install scrubber on medium-capacity fuel-switching ships, and carry out more LNG dual-fuel engine retrofits for large-capacity fuel-switching ships. Compared with SLP, this robust strategy greatly reduces sulfur emissions while slightly pushing up carbon emissions.

Comparison of Single and Multiple Turnovers of SecYEG in Escherichia coli.

Precursor proteins are translocated across the cytoplasmic membrane in Escherichia coli by the general secretory, or Sec, pathway. The main components of the pathway are the integral membrane heterotrimeric SecYEG complex and the peripheral membrane ATPase, SecA. In this study, we have applied an in vitro assay using inverted cytoplasmic membrane vesicles to investigate the complex cycle that leads to translocation. We compared the apparent rate constants for nine precursors under two experimental conditions, single turnover and multiple turnovers. For each precursor, the rate constant for a single turnover was higher than for multiple turnovers, indicating that a different step limits the rate under the two conditions. We conclude that the rate-limiting step for a single turnover is an early step in the initial phase of transit through the channel, whereas the rate of multiple turnovers is limited by the resetting of the translocon. The presence of the chaperone SecB during multiple turnovers increased the maximal amplitude translocated for the three precursor species tested, pGBP, pPhoA, and proOmpA, and also increased the apparent rate constants for both pGBP and pPhoA. The rate constant for proOmpA was decreased by the presence of SecB.IMPORTANCE Vastly different experimental techniques and conditions have been used to study export in E. coli We demonstrated that altering experimental conditions can change the step that is observed during study. Investigators should consider specific experimental conditions when comparing data from different laboratories, as well as when comparing data from different experiments within a laboratory. We have shown that each precursor species has inherent properties that determine the translocation rate; thus generalizations from studies of a single species must be made with caution. A summary of advantages and disadvantages in use of nine precursors is presented.

His-Tagged Peptidiscs Enable Affinity Purification of the Membrane Proteome for Downstream Mass Spectrometry Analysis.

Characterization of the integral membrane proteome by mass spectrometry (MS) remains challenging due its high complexity and inherent insolubility. In a typical experiment, the cellular membranes are isolated, the proteins are solubilized and fractionated, and the detergent micelles are removed before MS analysis. Detergents are not compatible with mass spectrometry, however, and their removal from biological samples often results in reduced protein identification. As an alternative to detergents, we recently developed the peptidisc membrane mimetic, which allows entrapment of the cell envelope proteome into water-soluble particles, termed a "peptidisc library". Here, we employ a His-tagged version of the peptidisc peptide scaffold to enrich the reconstituted membrane proteome by affinity chromatography. This purification step reduces the sample complexity by depleting ribosomal and soluble proteins that often cosediment with cellular membranes. As a result, the peptidisc library is enriched in low-abundance membrane proteins. We apply this method to survey changes in the membrane proteome upon depletion of the SecDFyajC complex, the ancillary subunit of the Sec translocon. In the depleted strain, we detect increased membrane localization of the motor ATPase SecA, along with increased levels of an unannotated inner membrane protein, YibN. Together, these results demonstrate the utility of the peptidisc for global purification of membrane proteins and for monitoring change in the membrane proteome.

Diversity of the 'Candidatus Phytoplasma asteris' and 'Candidatus Phytoplasma fraxini' isolates that infect urban trees in Bogotá, Colombia.

Phytoplasmas have been associated with a disease that affects trees of at least 11 species from different botanic families in Bogotá, Colombia. 'Candidatus Phytoplasma asteris' and 'Candidatus Phytoplasma fraxini' are the major groups of phytoplasma in the area of Bogotá. In this study, the genetic diversity within 'Ca. P. asteris' and 'Ca. P. fraxini' was studied in five urban tree species: Croton species (Euphorbiaceae), Fraxinus uhdei (Oleaceae), Magnolia grandiflora (Magnoliaceae), Populus nigra (Salicaceae) and Quercus humboldtii (Fagaceae). Analyses of the 16S rRNA gene using nested PCR, RFLP and sequencing showed that phytoplasmas of 'Ca. P. asteris' could be assigned to: subgroup 16SrI-B; a new subgroup named 16SrI-AF, with a restriction pattern similar to that of 16SrI-B; and a new subgroup named 16SrI-AG, with a restriction pattern similar to that of 16SrI-K and 16SrI-AH with a restriction pattern similar to that of 16SrI-AC. 'Ca. P. fraxini' isolates belonged to a new subgroup named 16SrVII-G, with a restriction pattern similar to that of 16SrVII-A. To complement the identification of the phytoplasma strains, we amplified nonribosomal genes such as leuS and secA. Unexpectedly, it was observed that in 16 trees in which 16S rRNA gene analysis showed the presence of 'Ca. P. fraxini' only, the leuS or secA primers amplified sequences exclusively affiliated to 'Ca. P. asteris. In those plants, sequences belonging to 'Ca. P. fraxini' leuS or secA genes were not amplified. The present work contributes to the identification of novel strains of both species in Colombia, and supports previous suggestions that phytoplasmas in South America are highly variable.

Directed evolution of SecB chaperones toward toxin-antitoxin systems.

SecB chaperones assist protein export in bacteria. However, certain SecB family members have diverged to become specialized toward the control of toxin-antitoxin (TA) systems known to promote bacterial adaptation to stress and persistence. In such tripartite TA-chaperone (TAC) systems, the chaperone was shown to assist folding and to prevent degradation of its cognate antitoxin, thus facilitating inhibition of the toxin. Here, we used both the export chaperone SecB of Escherichia coli and the tripartite TAC system of Mycobacterium tuberculosis as a model to investigate how generic chaperones can specialize toward the control of TA systems. Through directed evolution of SecB, we have identified and characterized mutations that specifically improve the ability of SecB to control our model TA system without affecting its function in protein export. Such a remarkable plasticity of SecB chaperone function suggests that its substrate binding surface can be readily remodeled to accommodate specific clients.

First report of a subgroup 16SrII-D phytoplasma associated with Opuntia cylindrica fasciated disease in Oman.

Cacti are evergreen perennial succulent plants that are used as ornamental and hedge plants. The fruits and leaves are also used as forage in some areas (Dewir, 2016). Cactus species are susceptible to several pathogens, including phytoplasma. In March 2020, three cactus plants (Opuntia cylindrica) out of ten (30% incidence) exhibited phytoplasma symptoms, including stunted growth, fasciation in stems and cladodes, color changes of the tips of cladodes to purple, and having clusters of highly proliferating cladodes. The plants were located in the Botanic Garden at Sultan Qaboos University, Muscat, Oman (N:23º59'14"; E:58º16'34"). PCR assays were carried out on the DNA samples extracted from young cladodes of three each of symptomatic and asymptomatic plants using phytoplasma-universal 16S rRNA primers, P1/P7 in direct PCR followed by R16F2n/R16R2, P4/P7 in the nested PCR. Distilled water (DW) and Alfalfa witches' broom phytoplasma (AlfWB) were used as negative and positive controls in each assay, respectively. In addition, amplification of the partial translocase protein A (secA) gene in the symptomatic cactus samples was done using SecA-II-F1/SecA-II-R1 (targeting 2140 bp) followed by SecA-II-F1/SecAR4 (targeting 1510 bp) (Al-Subhi et al., 2018). All the symptomatic plants and the positive control were positive for both genes (16S and secA), but no amplification was observed from the asymptomatic samples and DW. Sequence analysis and similarity searches against BLASTn revealed that the phytoplasma 16S rRNA (MT327813) shared 100% sequence identity with that of 'Candidatus Phytoplasma aurantifolia' isolate CB04 (MT555412) from India. The secA gene sequence (MT331815) analysis showed 100% identity with Cicer arietinum phyllody (KX358585). The associated phytoplasma was designated as cactus fasciated phytoplasma (CFP). Phylogenetic trees based on CFP 16Sr rRNA,secA genes, and a combined phylogenetic tree showed clustering of the CFP with the 16SrII-D subgroup phytoplasmas. The association of the aster yellows and peanut witches'-broom phytoplasma groups with other cactus species has already been reported from Lebanon, Mexico, China, Italy and Egypt (Dewir, 2016). The 16SrII phytoplasma in association with O. cylindrica showing fasciated stem has been reported from Egypt (Omar et al., 2014). A series of diverse plant species in association with 16SrII-D phytoplasma has been reported from Oman (Al-Subhi et al., 2018). However, this is the first report of a cactus phytoplasma disease in Oman belonging to the 16SrII-D subgroup phytoplasmas. Some fasciated cactus species are attractive and therefore cultivated as new ornamental plants and transported around the world, which may pose a new threat to other economically important crops.