Azotosporobacter soli gen. nov., sp. nov., a novel nitrogen-fixing bacterium isolated from paddy soil.

A nitrogen-fixing strain designated SG130T was isolated from paddy soil in Fujian Province, China. Strain SG130T was Gram-staining-negative, rod-shaped, and strictly anaerobic. Strain SG130T showed the highest 16S rRNA gene sequence similarities with the type strains Dendrosporobacter quercicolus DSM 1736T (91.7%), Anaeroarcus burkinensis DSM 6283T (91.0%) and Anaerospora hongkongensis HKU 15T (90.9%). Furthermore, the phylogenetic and phylogenomic analysis also suggested strain SG130T clustered with members of the family Sporomusaceae and was distinguished from other genera within this family. Growth of strain SG130T was observed at 25-45 °C (optimum 30 °C), pH 6.0-9.5 (optimum 7.0) and 0-1% (w/v) NaCl (optimum 0.1%). The quinones were Q-8 and Q-9. The polar lipids were phosphatidylserine (PS), phosphatidylethanolamine (PE), glycolipid (GL), phospholipid (PL) and an unidentified lipid (UL). The major fatty acids (> 10%) were iso-C13:0 3OH (26.6%), iso-C17:1 (15.6%) and iso-C15:1 F (11.4%). The genomic DNA G + C content was 50.7%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T (ANI 68.0% and dDDH 20.3%) were both below the cut-off level for species delineation. The average amino acid identity (AAI) between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T was 63.2%, which was below the cut-off value for bacterial genus delineation (65%). Strain SG130T possessed core genes (nifHDK) involved in nitrogen fixation, and nitrogenase activity (106.38 µmol C2H4 g-1 protein h-1) was examined using the acetylene reduction assay. Based on the above results, strain SG130T is confirmed to represent a novel genus of the family Sporomusaceae, for which the name Azotosporobacter soli gen. nov., sp. nov. is proposed. The type strain is SG130T (= GDMCC 1.3312T = JCM 35641T).

Salicylic Acid's impact on Sedum alfredii growth and cadmium tolerance: Comparative physiological, transcriptomic, and metabolomic study.

With the acceleration of industrialization, Cd pollution has emerged as a major threat to soil ecosystem health and food safety. Hyperaccumulating plants like Sedum alfredii Hance are considered to be used as part of an effective strategy for the ecological remediation of Cd polluted soils. This study delved deeply into the physiological, transcriptomic, and metabolomic responses of S. alfredii under cadmium (Cd) stress when treated with exogenous salicylic acid (SA). We found that SA notably enhanced the growth of S. alfredii and thereby increased absorption and accumulation of Cd, effectively alleviating the oxidative stress caused by Cd through upregulation of the antioxidant system. Transcriptomic and metabolomic data further unveiled the influence of SA on photosynthesis, antioxidant defensive mechanisms, and metal absorption enrichment pathways. Notably, the interactions between SA and other plant hormones, especially IAA and JA, played a central role in these processes. These findings offer us a comprehensive perspective on understanding how to enhance the growth and heavy metal absorption capabilities of hyperaccumulator plants by regulating plant hormones, providing invaluable strategies for future environmental remediation efforts.

Pesticides in the environment: Degradation routes, pesticide transformation products and ecotoxicological considerations.

Among rising environmental concerns, emerging contaminants constitute a variety of different chemicals and biological agents. The composition, residence time in environmental media, chemical interactions, and toxicity of emerging contaminants are not fully known, and hence, their regulation becomes problematic. Some of the important groups of emerging contaminants are pesticides and pesticide transformation products (PTPs), which present a considerable obstacle to maintaining and preserving ecosystem health. This review article aims to thoroughly comprehend the occurrence, fate, and ecotoxicological importance of pesticide transformation products (PTPs). The paper provides an overview of pesticides and PTPs as contaminants of emerging concern and discusses the modes of degradation of pesticides, their properties and associated risks. The degradation of pesticides, however, does not lead to complete destruction but can instead lead to the generation of PTPs. The review discusses the properties and toxicity of PTPs and presents the methods available for their detection. Moreover, the present study examines the existing regulatory framework and suggests the need for the development of new technologies for easy, routine detection of PTPs to regulate them effectively in the environment.

Physiology and transcriptomic analysis revealed the mechanism of silicon promoting cadmium accumulation in Sedum alfredii Hance.

Silicon (Si) effectively promote the yield of many crops, mainly due to its ability to enhance plants resistance to stress. However, how Si helps hyperaccumulators to extract Cadmium (Cd) from soil has remained unclear. In this study, Sedum alfredii Hance (S. alfredii) was used as material to study how exogenous Si affected biomass, Cd accumulation, antioxidation, cell ultrastructure, subcellular distribution and changes in gene expression after Cd exposure. The study has shown that as Si concentration increases (1, 2 mM), the shoot biomass of plants increased by 33.1% - 63.6%, the Cd accumulation increased by 31.9% - 96.6%, and the chlorophyll, carotenoid content, photosynthetic gas exchange parameters significantly increased. Si reduced Pro and MDA, promoted the concentrations of SOD, CAT and POD to reduce antioxidant stress damage. In addition, Si promoted GSH and PC to chelate Cd in vacuoles, repaired damaged cell ultrastructure, improved the fixation of Cd and cell wall (especially in pectin), and reduced the toxic effects of Cd. Transcriptome analysis found that genes encoding Cd detoxification, Cd absorption and transport were up-regulated by Si supplying, including photosynthetic pathways (PSB, LHCB, PSA), antioxidant defense systems (CAT, APX, CSD, RBOH), cell wall biosynthesis such as pectinesterase (PME), chelation (GST, MT, NAS, GR), Cd absorption (Nramp3, Nramp5, ZNT) and Cd transport (HMA, PCR). Our result revealed the tentative mechanism of Si promotes Cd accumulation and enhances Cd tolerance in S. alfredii, and thereby provides a solid theoretical support for the practical use of Si fertilizer in phytoextraction.

Jasmonic acid's impact on Sedum alfredii growth and cadmium tolerance: A physiological and transcriptomic study.

Soil cadmium (Cd) pollution is escalating, necessitating effective remediation strategies. This study investigated the effects of exogenous jasmonic acid (JA) on Sedum alfredii Hance under Cd stress, aiming to enhance its phytoextraction efficiency. Initially, experiments were conducted to assess the impact of various concentrations of JA added to environments with Cd concentrations of 100, 300, and 500 µmol/L. The results determined that a concentration of 1 µmol/L JA was optimal. This concentration effectively mitigated the level of ROS products by enhancing the activity of antioxidant enzymes. Additionally, JA fostered Cd absorption and accumulation, while markedly improving plant biomass and photosynthetic performance. In further experiments, treatment with 1 µmol/L JA under 300 µmol/L Cd stress was performed and transcriptomic analysis unveiled a series of differentially expressed genes (DEGs) instrumental in the JA-mediated Cd stress response. These DEGs encompass not only pathways of JA biosynthesis and signaling but also genes encoding functions that influence antioxidant systems and photosynthesis, alongside genes pertinent to cell wall synthesis, and metal chelation and transport. This study highlights that JA treatment significantly enhances S. alfredii's Cd tolerance and accumulation, offering a promising strategy for plant remediation and deepening our understanding of plant responses to heavy metal stress.

Selenite reduced cadmium uptake, interfered signal transduction of endogenous phytohormones, and stimulated secretion of tartaric acid based on a combined analysis of non-invasive micro-test technique, transcriptome and metabolome.

Selenium (Se) can reduce uptake and translocation of cadmium (Cd) in plants via plenty of ways, including regulation of root morphology. However, the underlying mechanisms on how Se will regulate root morphology under metal(loid) stresses are not fully illustrated. To fill up this knowledge gap, we investigated the effects of 0.5 mg L-1 selenite (Se(IV)) on root exudates, root morphology, root endogenous hormones, and Cd uptake efficiency of rice under the 1 mg L-1 Cd stress condition. The results showed that Se(IV) significantly reduced shoot and root Cd concentrations, and decreased Cd uptake efficiency via root hairs determined by a non-invasive micro-test (NMT) technology. When compared to the 1 mg L-1 Cd (Cd1) treatment, addition of 0.5 mg L-1 Se(IV) (1) significantly reduced root surface area and tip numbers, and non-significantly reduced root length, but significantly enhanced root diameter and root volume; (2) significantly enhanced concentrations of tartaric acid in the root exudate solution, root auxin (IAA) and root jasmonic acid (JA) via a UHPLC or a HPLC analysis; (3) significantly up-regulated metabolites correlated with synthesis of IAA, JA, gibberellin (GA), and salicylic acid, such as GA53, M-SA, (+/-)7-epi-JA, and derivatives of tryptophan and indole in the metabolome analysis. However, results of transcriptome analysis showed that (1) no upregulated differentially expressed genes (DEGs) were enriched in IAA synthesis; (2) some upregulated DEGs were found to be enriched in JA and GA53 synthesis pathways. In summary, although Se(IV) stimulated the synthesis of IAA, JA, and GA53, it significantly inhibited root growth mainly by 1) affecting signal transduction of IAA and GA; 2) altering IAA polar transport and homeostasis; and 3) regulating DEGs including SAUR32, SAUR36, SAUR76, OsSub33, OsEXPA8, OsEXPA18, and Os6bglu24.

Prevalence of antibiotic and metal resistance genes in phytoremediated cadmium and zinc contaminated soil assisted by chitosan and Trichoderma harzianum.

Heavy metal in soil have been shown to be toxic with high concentrations and acts as selective pressure on both bacterial metal and antibiotic resistance determinants, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) were applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of antibiotic and metal resistance genes (ARGs and MRGs) in the soil was also evaluated using metagenomic approach. Results indicated that the phytoremediation of Cd and Zn contaminated soil was promoted by Chi, and Tri further reinforced this effect, along with the increased availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and ß-lactam resistance genes) and maintained a high level of MRGs (e.g., chromium, copper) in soil. Soil available Zn and Cd fractions were the main factors contributing to ARGs profile by co-selection, while boosted bacterial hosts (e.g., Mitsuaria, Solirubrobacter, Ramlibacter) contributed to prevalence of most MRGs (e.g., Cd). These findings indicate the potential risk of ARGs and MRGs propagation in phytoremediation of metal contaminated soils assisted by organic and biological agents.

Metal-non-tolerant ecotypes of ectomycorrhizal fungi can protect plants from cadmium pollution.

The application of mycorrhizal fungi as a bioaugmentation technology for phytoremediation of heavy metal (HM) contaminated soil has attracted widespread attention. In order to explore whether the adaptation of Pinus massoniana (P. massoniana) to metal polluted soil depends on the metal adaptation potential of their associated ectomycorrhizal fungi (ECMF), we evaluated the cadmium (Cd) tolerance of 10 ecotypes of Cenococcum geophilum (C. geophilum) through a membership function method, and P. massoniana seedlings were not (NM) or inoculated by Cd non-tolerant type (JaCg144), low-tolerant (JaCg32, JaCg151) and high-tolerant (JaCg205) isolates of C. geophilum were exposed to 0 and 100 mg·kg-1 for 3 months. The result showed that, each ecotype of C. geophilum significantly promoted the growth, photosynthesis and chlorophyll content, proline (Pro) content and the activity of peroxidase (POD) of P. massoniana seedlings, and decreased malonaldehyde (MDA) content and catalase (CAT) and superoxide dismutase (SOD) activity. The comprehensive evaluation D value of the tolerance to Cd stress showed that the order of the displaced Cd resistance of the four ecotypic mycorrhizal P. massoniana was: JaCg144 > JaCg151 > JaCg32 > JaCg205. Pearson correlation analysis showed that the Sig. value of the comprehensive evaluation (D) values of the strains and mycorrhizal seedlings was 0.077 > 0.05, indicating that the Cd tolerance of the the C. geophilum isolates did not affect its regulatory effect on the Cd tolerance of the host plant. JaCg144 and JaCg151 which are non-tolerant and low-tolerant ecotype significantly increased the Cd content in the shoots and roots by about 136.64-181.75% and 153.75-162.35%, indicating that JaCg144 and JaCg151 were able to effectively increase the enrichment of Cd from the soil to the root. Transcriptome results confirmed that C. geophilum increased the P. massoniana tolerance to Cd stress through promoting antioxidant enzyme activity, photosynthesis, and lipid and carbohydrate synthesis metabolism. The present study suggests that mental-non-tolerant ecotypes of ECMF can protect plants from Cd pollution, providing more feasible strategies for ectomycorrhizal-assisted phytoremediation.

Selenite affected photosynthesis of Oryza sativa L. exposed to antimonite: Electron transfer, carbon fixation, pigment synthesis via a combined analysis of physiology and transcriptome.

Selenium (Se) is a microelement that can counteract (a)biotic stresses in plants. Excess antimony (Sb) will inhibit plant photosynthesis, which can be alleviated by appropriate doses of Se but the associated mechanisms at the molecular levels have not been fully explored. Here, a rice variety (Yongyou 9) was exposed to selenite [Se(IV), 0.2 and 0.8 mg L-1] alone or combined with antimonite [Sb(III), 5 and 10 mg L-1]. When compared to the 10 mg L-1 Sb treatment alone, addition of Se in a dose-dependent manner 1) reduced the heat dissipation efficiency resulting from the inhibited donors, Sb concentrations in shoots and roots, leaf concentrations of fructose, H2O2 and O2•-; 2) enhanced heat dissipation efficiency resulting from the inhibited accepters value, concentrations of Chl a, sucrose and starch, and the enzyme activity of adenosine diphosphate glucose pyrophosphorylase, sucrose phosphate synthase, and sucrose synthase; but 3) did not alter gas exchange parameters, concentrations of Chl b and total Chl, enzyme activity of soluble acid invertase, and values of maximum P700 signal, photochemical efficiency of PSI and electron transport rate of PSI. Se alleviated the damage caused by Sb to the oxygen-evolving complex and promoted the transfer of electrons from QA to QB. When compared to the 10 mg L-1 Sb treatment alone, addition of Se 1) up-regulated genes correlated to synthesis pathways of Chl, carotenoid, sucrose and glucose; 2) disturbed signal transduction pathway of abscisic acid; and 3) upregulated gene expression correlated to photosynthetic complexes (OsFd1, OsFER1 and OsFER2).

Exogenous silicon promotes cadmium (Cd) accumulation in Sedum alfredii Hance by enhancing Cd uptake and alleviating Cd toxicity.

Soil Cadmium (Cd) pollution has become a serious environmental problem. Silicon (Si) plays key roles in alleviating Cd toxicity in plants. However, the effects of Si on mitigation of Cd toxicity and accumulation of Cd by hyperaccumulators are largely unknown. This study was conducted to investigate the effect of Si on Cd accumulation and the physiological characteristics of Cd hyperaccumulator Sedum alfredii Hance under Cd stress. Results showed that, exogenous Si application promoted the biomass, Cd translocation and concentration of S. alfredii, with an increased rate of 21.74-52.17% for shoot biomass, and 412.39-621.00% for Cd accumulation. Moreover, Si alleviated Cd toxicity by: (i) increasing chlorophyll contents, (ii) improving antioxidant enzymes, (iii) enhancing cell wall components (lignin, cellulose, hemicellulose and pectin), (iv) raising the secretion of organic acids (oxalic acid, tartaric acid and L-malic acid). The RT-PCR analysis of genes that involved in Cd detoxification showed that the expression of SaNramp3, SaNramp6, SaHMA2 and SaHMA4 in roots were significantly decreased by 11.46-28.23%, 6.61-65.19%, 38.47-80.87%, 44.80-69.85% and 33.96-71.70% in the Si treatments, while Si significantly increased the expression of SaCAD. This study expanded understanding on the role of Si in phytoextraction and provided a feasible strategy for assisting phytoextraction Cd by S. alfredii. In summary, Si facilitated the Cd phytoextraction of S. alfredii by promoting plant growth and enhancing the resistance of plants to Cd.

Geothrix oryzisoli sp. nov., a ferric iron-reducing bacterium isolated from paddy soil.

An anaerobic, Gram-staining-negative, rod-shaped, Fe(III)-reducing strain, designated SG189T, was isolated from paddy soil in Fujian Province, China. Growth occurred at 20-35 ℃ (optimum 30 ℃), pH 6.5-8.0 (optimum 7.0) and 0-0.2% (w/v) NaCl (optimum 0%). The strain SG189T showed the highest 16S rRNA sequences similarities to the type strains of Geothrix fermentans DSM 14018T (98.9%), "Geothrix terrae" SG184T (99.0%) and "Geothrix alkalitolerans" SG263T (99.3%). ANI and dDDH values between strain SG189T and the most closely related Geothrix species were 86.5-87.1% and 31.5-32.9%, which lower than the cut-off values (ANI 95-96% and dDDH 70%) for prokaryotic species delineation. Further, genome-based phylogenomic trees constructed using 81 core genes (UBCG2) and 120 conserved genes (GTDB) showed that strain SG189T formed a clade with members of the genus Geothrix. The menaquinone was shown to be MK-8, and the major fatty acids were iso-C15:0 and iso-C13:0 3OH. The genomic DNA G + C content was 68.2%. Additionally, we found that strain SG189T possessed ability to reduce ferric iron, and strain SG189T could reduce 10 mM of ferric citrate in 10 days with lactate as the sole electron donor. Based on the observed physiological and biochemical properties, chemotaxonomic characteristics, ANI and dDDH values, SG189T represents a novel species of the genus Geothrix, for which the name Geothrix oryzisoli sp. nov. is proposed. The type strain is SG189T (= GDMCC 1.3408T = JCM 39324T).

A novel nitrogen-fixing bacterium, Propionivibrio soli sp. nov. isolated from paddy soil.

A facultative anaerobic nitrogen-fixing bacterium, designated SG131T, was isolated from paddy soil. Strain SG131T showed high 16S rRNA gene sequence similarities with type strains Propionivibrio limicola DSM 6832T (96.9%), Propionivibrio pelophilus asp 66T (96.0%) and Propionivibrio dicarboxylicus DSM 5885T (95.7%). The phylogenetic trees (based on 16S rRNA gene sequences and 120 conserved genes from genomes, respectively) indicated that strain SG131T clustered with members of the genus Propionivibrio. Growth of strain SG131T was observed at 25-40 °C, pH 5.5-10.5 and 0-0.5% (w/v) NaCl. The quinone was Q-7, and the main fatty acids were C16:1 ω6c and/or C16:1 ω7c (25.9%), C16:0 (23.3%), C17:0-cyclo (11.7%), C12:0 (6.0%) and C17:0 (5.9%). The genomic DNA G + C content of strain SG131T was 60.3%. The average nucleotide identity (ANI) values between strain SG131T and its most closely related species P. limicola DSM 6832T, P. pelophilus DSM 12018T and P. dicarboxylicus DSM 5885T were 74.4%, 74.9% and 75.6%, respectively. The digital DNA-DNA hybridization (dDDH) values between strain SG131T and its most closely related species P. limicola DSM 6832T, P. pelophilus DSM 12018T and P. dicarboxylicus DSM 5885T were 19.9%, 20.6% and 20.5%, respectively. All these values were lower than the recommended species delineation thresholds of ANI (95-96%) and dDDH (70%). Strain SG131T possessed core genes (nifHDK) of nitrogen fixation and was confirmed its nitrogen-fixing ability by the ARA method. According to the above-described analysis, strain SG131T represents a novel species of the genus Propionivibrio, for which the name Propionivibrio soli sp. nov. is proposed. The type strain is SG131T (= GDMCC 1.3313T = JCM 35595T).

Selenite reduced uptake/translocation of cadmium via regulation of assembles and interactions of pectins, hemicelluloses, lignins, callose and Casparian strips in rice roots.

Selenium (Se) can reduce cadmium (Cd) uptake/translocation via regulating pectins, hemicelluloses and lignins of plant root cell walls, but the detailed molecular mechanisms are not clear. In this study, six hydroponic experiments were set up to explore the relationships of uptake/translocation inhibition of Cd by selenite (Se(IV)) with cell wall component (CWC) synthesis and/or interactions. Cd and Se was supplied (alone or combinedly) at 1.0 mg L-1 and 0.5 mg L-1, respectively, with the treatment without Cd and Se as the control. When compared to the Cd1 treatment, the Se0.5Cd1 treatment 1) significantly increased total sugar concentrations in pectins, hemicelluloses and callose, suggesting an enhanced capacity of binding Cd or blocking Cd translocation; 2) stimulated the deposition of Casparian strips (CS) in root endodermis and exodermis to block Cd translocation; 3) stimulated the release of C-O-C (-OH- or -O-) and CO (carboxyl, carbonyl, or amide) to combine Cd; 4) regulated differential expression genes (DEGs) and metabolites (DMs) correlated with synthesis and/or interactions of CWSs to affect cell wall net structure to affect root cell division, subsequent root morphology and finally elemental uptake; and 5) stimulated de-methylesterification of pectins via reducing expression abundances of many DMs and DEGs in the Yang Cycle to reduce supply of methyls to homogalacturonan, and regulated gene expressions of pectin methylesterase to release carboxyls to combine Cd; and 6) down-regulated gene expressions associated with Cd uptake/translocation.

Comparative Physiological and Transcriptome Analysis Provide Insights into the Response of Cenococcum geophilum, an Ectomycorrhizal Fungus to Cadmium Stress.

Cadmium (Cd) displays strong toxicity, high mobility, and cannot be degraded, which poses a serious threat to the environment. Cenococcum geophilum (C. geophilum) is one of the most common ectomycorrhizal fungi (ECMF) in the natural environment. In this study, three Cd sensitive and three Cd tolerant strains of C. geophilum were used to analyze the physiological and molecular responses to Cd exposure. The results showed that Cd inhibited the growth of all strains of C. geophilum but had a less toxic effect on the tolerant strains, which may be correlated to a lower content of Cd and higher activity of antioxidant enzymes in the mycelia of tolerant strains. Comparative transcriptomic analysis was used to identify differentially expressed genes (DEGs) of four selected C. geophilum strains after 2 mg/L Cd treatment. The results showed that the defense response of C. geophilum strain to Cd may be closely related to the differential expression of functional genes involved in cell membrane ion transport, macromolecular compound metabolism, and redox pathways. The results were further confirmed by RT-qPCR analysis. Collectively, this study provides useful information for elucidation of the Cd tolerance mechanism of ECMF.

Toxicity of different forms of antimony to rice plants: Photosynthetic electron transfer, gas exchange, photosynthetic efficiency, and carbon assimilation combined with metabolome analysis.

Antimony (Sb) is a toxic metalloid, and excess Sb causes damage to the plant photosynthetic system. However, the underlying mechanisms of Sb toxicity in the plant photosynthetic system are not clear. Hydroponic culture experiments were conducted to illustrate the toxicity differences of antimonite [Sb(III)] and antimonate [Sb(V)] to the photosynthetic system in a rice plant (Yangdao No. 6). The results showed that Sb(III) showed a higher toxicity than Sb(V), judging from (1) lower shoot and root biomass, leaf water moisture content, water use efficiency, stomatal conductance, net photosynthetic rate, and transpiration rate; (2) higher water vapor deficit, soluble sugar content, starch content, and oligosaccharide content (sucrose, stachyose, and 1-kestose). To further analyze the direction of the photosynthetic products, we conducted a metabonomic analysis. More glycosyls were allocated to the synthesis pathways of oligosaccharides (sucrose, stachyose, and 1-kestose), anthocyanins, salicylic acid, flavones, flavonols, and lignin under Sb stress to quench excess oxygen free radicals (ROS), strengthen the cell wall structure, rebalance the cell membrane, and/or regulate cell permeability. This study provides a complete mechanism to elucidate the toxicity differences of Sb(III) and Sb(V) by exploring their effects on photosynthesis, saccharide synthesis, and the subsequent flow directions of glycosyls.

Isolation of Anaerobic Bromate-Reducing Bacteria Using Different Carbon Sources and Transcriptomic Insights From Klebsiella variicola Glu3.

Bromate, a possible human carcinogen, can be reduced to innocuous bromide by microorganisms. To characterize bromate reducers, microbes were enriched anaerobically from activated sludge by using bromate as the sole electron acceptor and different carbon sources as the electron donor. Bacteria that showed significant bromate-reducing activity but not coupled to cell growth were isolated. Two whole genomes of the isolates, namely, Raoultella electrica Lac1 and Klebsiella variicola Glu3, were reconstructed by Illumina and Nanopore sequencing. Transcriptomic analysis suggested that neither the respiratory nitrate reductase, the selenate reductase, nor the dimethylsulfoxide reductase was involved in the bromate reduction process, and strain K. variicola Glu3 reduced bromate via a yet undiscovered enzymatic mechanism. The results provide novel phylogenetic insights into bromate-reducing microorganisms and clues in putative genes encoding enzymes related to bromate reduction.

As(III) Exposure Induces a Zinc Scarcity Response and Restricts Iron Uptake in High-Level Arsenic-Resistant Paenibacillus taichungensis Strain NC1.

The Gram-positive bacterium Paenibacillus taichungensis NC1 was isolated from the Zijin gold-copper mine and shown to display high resistance to arsenic (MICs of 10 mM for arsenite in minimal medium). Genome sequencing indicated the presence of a number of potential arsenic resistance determinants in NC1. Global transcriptomic analysis under arsenic stress showed that NC1 not only directly upregulated genes in an arsenic resistance operon but also responded to arsenic toxicity by increasing the expression of genes encoding antioxidant functions, such as cat, perR, and gpx. In addition, two highly expressed genes, marR and arsV, encoding a putative flavin-dependent monooxygenase and located adjacent to the ars resistance operon, were highly induced by As(III) exposure and conferred resistance to arsenic and antimony compounds. Interestingly, the zinc scarcity response was induced under exposure to high concentrations of arsenite, and genes responsible for iron uptake were downregulated, possibly to cope with oxidative stress associated with As toxicity. IMPORTANCE Microbes have the ability to adapt and respond to a variety of conditions. To better understand these processes, we isolated the arsenic-resistant Gram-positive bacterium Paenibacillus taichungensis NC1 from a gold-copper mine. The transcriptome responding to arsenite exposure showed induction of not only genes encoding arsenic resistance determinants but also genes involved in the zinc scarcity response. In addition, many genes encoding functions involved in iron uptake were downregulated. These results help to understand how bacteria integrate specific responses to arsenite exposure with broader physiological responses.

The PI3K/AKT Pathway and PTEN Gene Are Involved in "Tree-Top Disease" of Lymantria dispar.

Nucleopolyhedrovirus (NPV) can alter its host behaviour such that infected larvae hang at the top of trees before their death. This phenomenon was firstly described by Hofmann in 1891 and named as "tree-top disease". Subsequent studies have described effects during the infection proceedings as NPVs manipulate the host to avoid the immune response, cross defensive barriers and regulate hormones. In this study, we demonstrate that the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway is involved in host manipulation by Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV). Particularly at the late stage of infection, a multifunctional dephosphorylase in the PI3K/AKT signaling pathway is dynamically upregulated, namely, the phosphatidylinositol-3, 4, 5-trisphosphate 3-phosphatase and dual-specificity protein phosphatase (PTEN) gene. The biological assays of PTEN gene knockdown showed that an increase in PTEN gene expression was necessary for the infected Lymantria dispar larvae's terminal climbing behavior, death postponement and virion production. The results imply that the PI3K/AKT signaling pathway and PTEN gene might play an essential role in "tree-top disease" induced by LdMNPV.

Identification of a MarR Subfamily That Regulates Arsenic Resistance Genes.

In this study, comprehensive analyses were performed to determine the function of an atypical MarR homolog in Achromobacter sp. strain As-55. Genomic analyses of Achromobacter sp. As-55 showed that this marR is located adjacent to an arsV gene. ArsV is a flavin-dependent monooxygenase that confers resistance to the antibiotic methylarsenite [MAs(III)], the organoarsenic compound roxarsone(III) [Rox(III)], and the inorganic antimonite [Sb(III)]. Similar marR genes are widely distributed in arsenic-resistant bacteria. Phylogenetic analyses showed that these MarRs are found in operons predicted to be involved in resistance to inorganic and organic arsenic species, so the subfamily was named MarRars. MarRars orthologs have three conserved cysteine residues, which are Cys36, Cys37, and Cys157 in Achromobacter sp. As-55, mutation of which compromises the response to MAs(III)/Sb(III). GFP-fluorescent biosensor assays show that AdMarRars (MarR protein of Achromobacter deleyi As-55) responds to trivalent As(III) and Sb(III) but not to pentavalent As(V) or Sb(V). The results of RT-qPCR assays show that arsV is expressed constitutively in a marR deletion mutant, indicating that marR represses transcription of arsV. Moreover, electrophoretic mobility shift assays (EMSAs) demonstrate that AdMarRars binds to the promoters of both marR and arsV in the absence of ligands and that DNA binding is relieved upon binding of As(III) and Sb(III). Our results demonstrate that AdMarRars is a novel As(III)/Sb(III)-responsive transcriptional repressor that controls expression of arsV, which confers resistance to MAs(III), Rox(III), and Sb(III). AdMarRars and its orthologs form a subfamily of MarR proteins that regulate genes conferring resistance to arsenic-containing antibiotics. IMPORTANCE In this study, a MarR family member, AdMarRars was shown to regulate the arsV gene, which confers resistance to arsenic-containing antibiotics. It is a founding member of a distinct subfamily that we refer to as MarRars, regulating genes conferring resistance to arsenic and antimony antibiotic compounds. AdMarRars was shown to be a repressor containing conserved cysteine residues that are required to bind As(III) and Sb(III), leading to a conformational change and subsequent derepression. Here we show that members of the MarR family are involved in regulating arsenic-containing compounds.