Sustained bacterial N2O reduction at acidic pH.

Nitrous oxide (N2O) is a climate-active gas with emissions predicted to increase due to agricultural intensification. Microbial reduction of N2O to dinitrogen (N2) is the major consumption process but microbial N2O reduction under acidic conditions is considered negligible, albeit strongly acidic soils harbor nosZ genes encoding N2O reductase. Here, we study a co-culture derived from acidic tropical forest soil that reduces N2O at pH 4.5. The co-culture exhibits bimodal growth with a Serratia sp. fermenting pyruvate followed by hydrogenotrophic N2O reduction by a Desulfosporosinus sp. Integrated omics and physiological characterization revealed interspecies nutritional interactions, with the pyruvate fermenting Serratia sp. supplying amino acids as essential growth factors to the N2O-reducing Desulfosporosinus sp. Thus, we demonstrate growth-linked N2O reduction between pH 4.5 and 6, highlighting microbial N2O reduction potential in acidic soils.

Comparative genomics of plant growth promoting phosphobacteria isolated from acidic soils.

Despite being one of the most abundant elements in soil, phosphorus (P) often becomes a limiting macronutrient for plants due to its low bioavailability, primarily locked away in insoluble organic and inorganic forms. Phosphate solubilizing and mineralizing bacteria, also called phosphobacteria, isolated from P-deficient soils have emerged as a promising biofertilizer alternative, capable of converting these recalcitrant P forms into plant-available phosphates. Three such phosphobacteria strains-Serratia sp. RJAL6, Klebsiella sp. RCJ4, and Enterobacter sp. 198-previously demonstrated their particular strength as plant growth promoters for wheat, ryegrass, or avocado under abiotic stresses and P deficiency. Comparative genomic analysis of their draft genomes revealed several genes encoding key functionalities, including alkaline phosphatases, isonitrile secondary metabolites, enterobactin biosynthesis and genes associated to the production of indole-3-acetic acid (IAA) and gluconic acid. Moreover, overall genome relatedness indexes (OGRIs) revealed substantial divergence between Serratia sp. RJAL6 and its closest phylogenetic neighbours, Serratia nematodiphila and Serratia bockelmanii. This compelling evidence suggests that RJAL6 merits classification as a novel species. This in silico genomic analysis provides vital insights into the plant growth-promoting capabilities and provenance of these promising PSRB strains. Notably, it paves the way for further characterization and potential application of the newly identified Serratia species as a powerful bioinoculant in future agricultural settings.

Mosquito Microbiomes of Rwanda: Characterizing Mosquito Host and Microbial Communities in the Land of a Thousand Hills.

Mosquitoes are a complex nuisance around the world and tropical countries bear the brunt of the burden of mosquito-borne diseases. Rwanda has had success in reducing malaria and some arboviral diseases over the last few years, but still faces challenges to elimination. By building our understanding of in situ mosquito communities in Rwanda at a disturbed, human-occupied site and at a natural, preserved site, we can build our understanding of natural mosquito microbiomes toward the goal of implementing novel microbial control methods. Here, we examined the composition of collected mosquitoes and their microbiomes at two diverse sites using Cytochrome c Oxidase I sequencing and 16S V4 high-throughput sequencing. The majority (36 of 40 species) of mosquitoes captured and characterized in this study are the first-known record of their species for Rwanda but have been characterized in other nations in East Africa. We found significant differences among mosquito genera and among species, but not between mosquito sexes or catch method. Bacteria of interest for arbovirus control, Asaia, Serratia, and Wolbachia, were found in abundance at both sites and varied greatly by species.

Microbial Community Changes in Silkworms Suspected of Septicemia and Identification of Serratia sp.

Diseases that occur in silkworms include soft rot, hardening disease, digestive diseases, and sepsis. However, research on the causes of bacterial diseases occurring in silkworms and the resulting changes in the microbial community is lacking. Therefore, we examined the morphological characteristics of sepsis and changes in the microbial community between silkworms that exhibit a unique odor and healthy silkworms; thus, we established a relationship between disease-causing microorganisms and sepsis. After producing a 16S rRNA amplicon library for samples showing sepsis, we obtained information on the microbial community present in silkworms using next-generation sequencing. Compared to that in healthy silkworms, in silkworms with sepsis, the abundance of the Firmicutes phylum was significantly reduced, while that of Proteobacteria was increased. Serratia sp. was dominant in silkworms with sepsis. After bacterial isolation, identification, and reinfection through the oral cavity, we confirmed this organism as the disease-causing agent; its mortality rate was 1.8 times higher than that caused by Serratia marcescens. In summary, we identified a new causative bacterium of silkworm sepsis through microbial community analysis and confirmed that the microbial community balance was disrupted by the aberrant proliferation of certain bacteria.

Effects of biochar immobilization of Serratia sp. F4 OR414381 on bioremediation of petroleum contamination and bacterial community composition in loess soil.

Petroleum hydrocarbons pose a significant threat to human health and the environment. Biochar has increasingly been utilized for soil remediation. This study investigated the potential of biochar immobilization using Serratia sp. F4 OR414381 for the remediation of petroleum-contaminated soil through a pot experiment conducted over 90 days. The treatments in this study, denoted as IMs (maize straw biochar-immobilized Serratia sp. F4), degraded 82.5% of the total petroleum hydrocarbons (TPH), 59.23% of the aromatic, and 90.1% of the saturated hydrocarbon fractions in the loess soils. During remediation, the soil pH values decreased from 8.76 to 7.33, and the oxidation-reduction potential (ORP) increased from 156 to 229 mV. The treatment-maintained soil nutrients of the IMs were 138.94 mg/kg of NO3- -N and 92.47 mg/kg of available phosphorus (AP), as well as 11.29% of moisture content. The activities of soil dehydrogenase (SDHA) and catalase (CAT) respectively increased by 14% and 15 times compared to the CK treatment. Three key petroleum hydrocarbon degradation genes, including CYP450, AJ025, and xylX were upregulated following IMs treatment. Microbial community analysis revealed that a substantial microbial population of 1.01E+ 09 cells/g soil and oil-degrading bacteria such as Salinimicrobium, Saccharibacteria_genera_incertae_sedis, and Brevundimonas were the dominant genera in IMs treatment. This suggests that the biochar immobilized on Serratia sp. F4 OR414381 improves soil physicochemical properties and enhances interactions among microbial populations, presenting a promising and environmentally friendly approach for the stable and efficient remediation of petroleum-contaminated loess soil.

First report of blaOXA-181-carrying IncX3 plasmids in multidrug-resistant Enterobacter hormaechei and Serratia nevei recovered from canine and feline opportunistic infections.

Whole-genome sequence analysis of six Enterobacter hormaechei and two Serratia nevei strains, using a hybrid assembly of Illumina and Oxford Nanopore Technologies sequencing, revealed the presence of the epidemic blaOXA-181-carrying IncX3 plasmids co-harboring qnrS1 and ∆ere(A) genes, as well as multiple multidrug resistance (MDR) plasmids disseminating in all strains, originated from dogs and cats in Thailand. The subspecies and sequence types (ST) of the E. hormaechei strains recovered from canine and feline opportunistic infections included E. hormaechei subsp. xiangfangensis ST171 (n = 3), ST121 (n = 1), and ST182 (n = 1), as well as E. hormaechei subsp. steigerwaltii ST65 (n = 1). Five of the six E. hormaechei strains harbored an identical 51,479-bp blaOXA-181-carrying IncX3 plasmid. However, the blaOXA-181 plasmid (pCUVET22-969.1) of the E. hormaechei strain CUVET22-969 presented a variation due to the insertion of ISKpn74 and ISSbo1 into the virB region. Additionally, the blaOXA-181 plasmids of S. nevei strains were nearly identical to the others at the nucleotide level, with ISEcl1 inserted upstream of the qnrS1 gene. The E. hormaechei and S. nevei lineages from canine and feline origins might acquire the epidemic blaOXA-181-carrying IncX3 and MDR plasmids, which are shared among Enterobacterales, contributing to the development of resistance. These findings suggest the spillover of significant OXA-181-encoding plasmids to these bacteria, causing severe opportunistic infections in dogs and cats in Thailand. Surveillance and effective hygienic practice, especially in hospitalized animals and veterinary hospitals, should be urgently implemented to prevent the spread of these plasmids in healthcare settings and communities. IMPORTANCE: blaOXA-181 is a significant carbapenemase-encoding gene, usually associated with an epidemic IncX3 plasmid found in Enterobacterales worldwide. In this article, we revealed six carbapenemase-producing (CP) Enterobacter hormaechei and two CP Serratia nevei strains harboring blaOXA-181-carrying IncX3 and multidrug resistance plasmids recovered from dogs and cats in Thailand. The carriage of these plasmids can promote extensively drug-resistant properties, limiting antimicrobial treatment options in veterinary medicine. Since E. hormaechei and S. nevei harboring blaOXA-181-carrying IncX3 plasmids have not been previously reported in dogs and cats, our findings provide the first evidence of dissemination of the epidemic plasmids in these bacterial species isolated from animal origins. Pets in communities can serve as reservoirs of significant antimicrobial resistance determinants. This situation places a burden on antimicrobial treatment in small animal practice and poses a public health threat.

Dynamic Gut Microbiota of Apolygus lucorum Across Different Life Stages Reveals Potential Pathogenic Bacteria for Facilitating the Pest Management.

Insect's gut microbiota has diverse effects on their fitness, and a comprehensive understanding of gut microbiota functions requires analyzing its diversity. Apolygus lucorum is a highly destructive pest that threatens many economically important crops in China. This study investigated the gut microbiota of A. lucorum across its life cycle using both culture-dependent and culture-independent methods. A total of 87 gut bacterial isolates were identified, belonging to 4 phyla, 27 families, and 45 genera, while Miseq sequencing detected 91 amplicon sequence variants (ASVs) assigned to 5 phyla, 28 families, and 39 genera. Proteobacteria and Firmicutes were the predominant phyla, with Staphylococcus and Serratia as the major genera. There were significant differences in the relative abundance of these genera between the nymph and adult stages. Staphylococcus was significantly more abundant in nymphs than it in adults, while Serratia was significantly more abundant in sexually mature adults than in other developmental stages. Notably, Serratia is a common opportunistic pathogen in many insects. Injecting the gut-dominant isolate Serratia marcescens verified its high pathogenicity. Additionally, immune indicators of the bug at different developmental stages supported the hypothesis that Serratia is a pathogen of A. lucorum. This study provides a foundation for understanding the role of gut bacteria in the life history of A. lucorum and developing new pest control strategies based on microbes.

In silico exploration of Serratia sp. BRL41 genome for detecting prodigiosin Biosynthetic Gene Cluster (BGC) and in vitro antimicrobial activity assessment of secreted prodigiosin.

The raising concern of drug resistance, having substantial impacts on public health, has instigated the search of new natural compounds with substantial medicinal activity. In order to find out a natural solution, the current study has utilized prodigiosin, a linear tripyrrole red pigment, as an active ingredient to control bacterial proliferation and prevent cellular oxidation caused by ROS (Reactive Oxygen Species). A prodigiosin-producing bacterium BRL41 was isolated from the ancient Barhind soil of BCSIR Rajshahi Laboratories, Bangladesh, and its morphological and biochemical characteristics were investigated. Whole genome sequencing data of the isolate revealed its identity as Serratia sp. and conferred the presence of prodigiosin gene cluster in the bacterial genome. "Prodigiosin NRPS", among the 10 analyzed gene clusters, showed 100% similarity with query sequences where pigC, pigH, pigI, and pigJ were identified as fundamental genes for prodigiosin biosynthesis. Some other prominent clusters for synthesis of ririwpeptides, yersinopine, trichrysobactin were also found in the chromosome of BRL41, whilst the rest displayed less similarity with query sequences. Except some first-generation beta-lactam resistance genes, no virulence and resistance genes were found in the genome of BRL41. Structural illumination of the extracted red pigment by spectrophotometric scanning, Thin-Layer Chromatography (TLC), Fourier Transform Infrared Spectroscopy (FTIR), and change of color at different pH solutions verified the identity of the isolated compound as prodigiosin. Serratia sp. BRL41 attained its maximum productivity 564.74 units/cell at temperature 30˚C and pH 7.5 in two-fold diluted nutrient broth medium. The compound exhibited promising antibacterial activity against Gram-positive and Gram-negative bacteria with MIC (Minimum Inhibitory Concentration) and MBC (Minimum Bactericidal Concentration) values ranged from 3.9 to15.62 µg/mL and 7.81 to 31.25 µg/mL respectively. At concentration 500 µg/mL, except in Salmonella enterica ATCC-10708, prodigiosin significantly diminished biofilm formed by Listeria monocytogens ATCC-3193, Pseudomonas aeruginosa ATCC-9027, Escherichia coli (environmental isolate), Staphylococcus aureus (environmental isolate). Cellular glutathione level (GSH) was elevated upon application of 250 and 500 µg/mL pigment where 125 µg/mL failed to show any free radical scavenging activity. Additionally, release of cellular components in growth media of both Gram-positive and Gram-negative bacteria were facilitated by the extract that might be associated with cell membrane destabilization. Therefore, the overall findings of antimicrobial, antibiofilm and antioxidant activities suggest that in time to come prodigiosin might be a potential natural source to treat various diseases and infections.

Genome-driven discovery of new serrawettin W2 analogues from Serratia fonticola DSM 4576.

By expressing a multimodular NRPS gene sefA from Serratia fonticola DSM 4576 in E. coli, four new serrawettin W2 analogues, namely sefopeptides A-D (1-4), were isolated and structurally characterized and their biosynthesis was proposed. A bioactivity assay showed that sefopeptide C (3) exhibits moderate cytotoxic activity against acute promyelocytic leukemia NB4 cells.

Rhs NADase effectors and their immunity proteins are exchangeable mediators of inter-bacterial competition in Serratia.

Many bacterial species use Type VI secretion systems (T6SSs) to deliver anti-bacterial effector proteins into neighbouring bacterial cells, representing an important mechanism of inter-bacterial competition. Specific immunity proteins protect bacteria from the toxic action of their own effectors, whilst orphan immunity proteins without a cognate effector may provide protection against incoming effectors from non-self competitors. T6SS-dependent Rhs effectors contain a variable C-terminal toxin domain (CT), with the cognate immunity protein encoded immediately downstream of the effector. Here, we demonstrate that Rhs1 effectors from two strains of Serratia marcescens, the model strain Db10 and clinical isolate SJC1036, possess distinct CTs which both display NAD(P)+ glycohydrolase activity but belong to different subgroups of NADase from each other and other T6SS-associated NADases. Comparative structural analysis identifies conserved functions required for NADase activity and reveals that unrelated NADase immunity proteins utilise a common mechanism of effector inhibition. By replicating a natural recombination event, we show successful functional exchange of CTs and demonstrate that Db10 encodes an orphan immunity protein which provides protection against T6SS-delivered SJC1036 NADase. Our findings highlight the flexible use of Rhs effectors and orphan immunity proteins during inter-strain competition and the repeated adoption of NADase toxins as weapons against bacterial cells.

A diversity of endosymbionts across Australian aphids and their persistence in aphid cultures.

There is increasing interest in the use of endosymbionts in pest control, which will benefit from the identification of endosymbionts from potential donor species for transfer to pest species. Here, we screened for endosymbionts in 123 Australian aphid samples across 32 species using 16S DNA metabarcoding. We then developed a qPCR method to validate the metabarcoding data set and to monitor endosymbiont persistence in aphid cultures. Pea aphids (Acyrthosiphon pisum) were frequently coinfected with Rickettsiella and Serratia, and glasshouse potato aphids (Aulacorthum solani) were coinfected with Regiella and Spiroplasma; other secondary endosymbionts detected in samples occurred by themselves. Hamiltonella, Rickettsia and Wolbachia were restricted to a single aphid species, whereas Regiella was found in multiple species. Rickettsiella, Hamiltonella and Serratia were stably maintained in laboratory cultures, although others were lost rapidly. The overall incidence of secondary endosymbionts in Australian samples tended to be lower than recorded from aphids overseas. These results indicate that aphid endosymbionts probably exhibit different levels of infectivity and vertical transmission efficiency across hosts, which may contribute to natural infection patterns. The rapid loss of some endosymbionts in cultures raises questions about factors that maintain them under field conditions, while endosymbionts that persisted in laboratory culture provide candidates for interspecific transfers.

Prodigiosin from Serratia rubidaea MJ 24 impedes Helicoverpa armigera development by the dysregulation of Juvenile hormone-dopamine system.

Prodigiosin pigment is a secondary metabolite produced by many bacterial species and is known for its medicinal properties. A few of these prodigiosin-producing bacteria are also reported to be entomopathogenic. It is intriguing to unravel the role of prodigiosin in insecticidal activities and its mode of action. In this study, we have shown the production and characterization of prodigiosin from the Serratia rubidaea MJ 24 isolated from the soil of the Western Ghats, India. Further, we assessed the effect of this pigment on the lepidopteran agricultural pest, Helicoverpa armigera. Prodigiosin-fed H. armigera indicated defective development of insect growth upon treatment. Due to defective early development, about 50% mortality and 40% reduction in body weight were observed in insects fed on a 500 ppm prodigiosin-containing diet. The transcriptomic analysis of these insects indicated significant dysregulation of Juvenile hormone synthesis and response related genes. In addition, dopamine related processes and their resultant melanization and sclerotization processes were also found to be affected. The changes in the expression levels of the key transcripts were further validated using real-time quantitative PCR. The metabolome data confirmed the developmental dysregulation of precursors and products of differentially regulated genes due to prodigiosin. Therefore, the corroborated data suggests that prodigiosin majorly affects H. armigera development through dysregulation of the Juvenile hormone-dopamine system and can be considered as a bioactive scaffold to design insect-pest management compounds. This study provides the first report of in-depth analysis of insecticidal system dynamics in H. armigera insects upon prodigiosin feeding via gene expression and metabolic change via omics approach.

Regulation of indole-3-acetic acid biosynthesis and consequences of auxin production deficiency in Serratia plymuthica.

Indole-3-acetic acid (IAA) is emerging as a key intra- and inter-kingdom signal molecule that modulates a wide range of processes of importance during plant-microorganism interaction. However, the mechanisms by which IAA carries out its functions in bacteria as well as the regulatory processes by which bacteria modulate auxin production are largely unknown. Here, we found that IAA synthesis deficiency results in important global transcriptional changes in the broad-range antibiotic-producing rhizobacterium Serratia plymuthica A153. Most pronounced transcriptional changes were observed in various gene clusters for aromatic acid metabolism, including auxin catabolism. To delve into the corresponding molecular mechanisms, different regulatory proteins were biochemically characterized. Among them, a TyrR orthologue was essential for IAA production through the activation of the ipdc gene encoding a key enzyme for IAA biosynthesis. We showed that TyrR specifically recognizes different aromatic amino acids which, in turn, alters the interactions of TyrR with the ipdc promoter. Screening of mutants defective in various transcriptional and post-transcriptional regulators allowed the identification of additional regulators of IAA production, including PigP and quorum sensing-related genes. Advancing our knowledge on the mechanisms that control the IAA biosynthesis in beneficial phytobacteria is of biotechnological interest for improving agricultural productivity and sustainable agricultural development.

Bioinformatic survey of CRISPR loci across 15 Serratia species.

The Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated proteins (CRISPR-Cas) system of prokaryotes is an adaptative immune defense mechanism to protect themselves from invading genetic elements (e.g., phages and plasmids). Studies that describe the genetic organization of these prokaryotic systems have mainly reported on the Enterobacteriaceae family (now reorganized within the order of Enterobacterales). For some genera, data on CRISPR-Cas systems remain poor, as in the case of Serratia (now part of the Yersiniaceae family) where data are limited to a few genomes of the species marcescens. This study describes the detection, in silico, of CRISPR loci in 146 Serratia complete genomes and 336 high-quality assemblies available for the species ficaria, fonticola, grimesii, inhibens, liquefaciens, marcescens, nematodiphila, odorifera, oryzae, plymuthica, proteomaculans, quinivorans, rubidaea, symbiotica, and ureilytica. Apart from subtypes I-E and I-F1 which had previously been identified in marcescens, we report that of I-C and the I-E unique locus 1, I-E*, and I-F1 unique locus 1. Analysis of the genomic contexts for CRISPR loci revealed mdtN-phnP as the region mostly shared (grimesii, inhibens, marcescens, nematodiphila, plymuthica, rubidaea, and Serratia sp.). Three new contexts detected in genomes of rubidaea and fonticola (puu genes-mnmA) and rubidaea (osmE-soxG and ampC-yebZ) were also found. The plasmid and/or phage origin of spacers was also established.

An OmpW-dependent T4-like phage infects Serratia sp. ATCC 39006.

Serratia sp. ATCC 39006 is a Gram-negative bacterium that has been used to study the function of phage defences, such as CRISPR-Cas, and phage counter-defence mechanisms. To expand our phage collection to study the phage-host interaction with Serratia sp. ATCC 39006, we isolated the T4-like myovirus LC53 in Otepoti Dunedin, Aotearoa New Zealand. Morphological, phenotypic and genomic characterization revealed that LC53 is virulent and similar to other Serratia, Erwinia and Kosakonia phages belonging to the genus Winklervirus. Using a transposon mutant library, we identified the host ompW gene as essential for phage infection, suggesting that it encodes the phage receptor. The genome of LC53 encodes all the characteristic T4-like core proteins involved in phage DNA replication and generation of viral particles. Furthermore, our bioinformatic analysis suggests that the transcriptional organization of LC53 is similar to that of Escherichia coli phage T4. Importantly, LC53 encodes 18 tRNAs, which likely compensate for differences in GC content between phage and host genomes. Overall, this study describes a newly isolated phage infecting Serratia sp. ATCC 39006 that expands the diversity of phages available to study phage-host interactions.

Serratia silvae sp. nov., Isolated from Forest Soil.

The Gram-negative, oxidase-negative, catalase-positive, rod-shaped strain Arafor3T was isolated from forest soil (France). Comparative 16S rRNA gene analysis and phylogenetic analysis based on (1) multilocus sequence analysis (MLSA) with four housekeeping genes (atpD, gyrB, infB and rpoB) and (2) genomes indicated that strain Arafor3T shared 98.83% 16S rRNA gene sequence similarity with the type strain of Serratia fonticola DSM 4576T and was closely related to this same strain in the MLSA and in the phylogenomic tree reconstruction. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) comparisons of strain Arafor3T with its nearest neighbor S. fonticola DSM 4576T showed 93.5% identity and 55.7% sequence similarity, respectively, and were lower than the 96% and 70% species-level cut-off values relating to these analyses (Logan et al. in Int J Syst Evol Microbiol 59:2114-21, 2009, https://doi.org/10.1099/ijs.0.013649-0 ). The strain differed from S. fonticola in that it was urease and arginine dihydrolase negative. The major fatty acids of strain Arafor3T are C16:0, C16:1 ω7c/C16:1 ω6c, C14:0, C14:0 3-OH/16:1 isoI, and C18:1 ω7c. The major respiratory quinone is Q8. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, and 6 unknown lipids. The mol G + C% content of the genomic DNA of strain Arafor3T was 53.49%. Hence, Arafor3T represents a novel species within the genus Serratia, for which the name Serratia silvae sp. nov. is proposed. The type strain is Arafor3T (=LMG 32338T = CIP 111939T).

Biological activity of volatiles produced by the strains of two Pseudomonas and two Serratia species.

Volatile compounds emitted by bacteria can play a significant role in interacting with microorganisms, plants, and other organisms. In this work, we studied the effect of total gaseous mixtures of organic as well as inorganic volatile compounds (VCs) and individual pure volatile organic compounds (VOCs: ketones 2-nonanone, 2-heptanone, 2-undecanone, a sulfur-containing compound dimethyl disulfide) synthesized by the rhizosphere Pseudomonas chlororaphis 449 and Serratia plymuthica IC1270 strains, the soil-borne strain P. fluorescens B-4117, and the spoiled meat isolate S. proteamaculans 94 strain on Arabidopsis thaliana plants (on growth and germination of seeds). We demonstrated that total mixtures of volatile compounds emitted by these strains grown on Luria-Bertani agar, Tryptone Soya Agar, and Potato Dextrose Agar media inhibited the A. thaliana growth. When studied bacteria grew on Murashige and Skoog (MS) agar medium, volatile mixtures produced by bacteria could stimulate the growth of plants. Volatile compounds of bacteria slowed down the germination of plant seeds; in the presence of volatile mixtures of P. fluorescens B-4117, the seeds did not germinate. Of the individual VOCs, 2-heptanone had the most potent inhibitory effect on seed germination. We also showed that the tested VOCs did not cause oxidative stress in Escherichia coli cells using specific lux-biosensors. VOCs reduced the expression of the lux operon from the promoters of the katG, oxyS, and soxS genes (whose products involved in the protection of cells from oxidative stress) caused by the action of hydrogen peroxide and paraquat, respectively.

Genome Sequence Resource of Serratia ureilytica HNU47: A Strain with Biocontrol Potential Against Bacterial Wilt Pathogen Ralstonia solanacearum.

Serratia ureilytica HNU47 was originally isolated from rhizosphere soil of stock in a continuous cropping tomato-planting field, which has excellent antagonistic ability against Ralstonia solanacearum. Here, we sequenced the genome of HNU47 to gain insights into the underlying basis of its antagonistic activity. Results of phylogenetic analysis of the whole genomic sequence demonstrated that HNU47 belongs to S. ureilytica. Through antiSMASH analysis, 10 secondary metabolite biosynthesis gene clusters were predicted. There were only two gene clusters with similarity higher than 95% with known compounds' gene clusters and the similarities of the other eight gene clusters were lower than 30%, including three gene clusters with no homology. In addition, biocontrol experiments confirmed that HNU47 could decrease the incidence of bacterial wilt caused by R. solanacearum on tomato. These findings support the potential of developing S. ureilytica HNU47 as a biocontrol agent against R. solanacearum by producing some unknown active compounds. The genome sequence reported here is also useful for revealing the modulation mechanisms underlying biosynthesis of active compounds.

Genetic Determinants of Antagonistic Interactions and the Response of New Endophytic Strain Serratia quinivorans KP32 to Fungal Phytopathogens.

Fungal phytopathogens are challenging to control due to their penetration into plant tissues. Therefore, plant-colonizing bacteria could serve as an excellent weapon in fighting fungal infections. In this study, we aim to determine the biocontrol potential of the new endophytic strain Serratia quinivorans KP32, isolated from the roots of Petroselinum crispum L.; identify the related mechanisms; and understand the basis of its antagonistic interaction with taxonomically diverse fungi at the molecular level. The KP32 strain presented biological activity against Rhizoctonia solani, Colletotrichum dematium, Fusarium avenaceum, and Sclerotinia sclerotiorum, and its ability to inhibit the growth of the phytopathogens was found to be mediated by a broad spectrum of biocontrol features, such as the production of a number of lytic enzymes (amylases, chitinases, and proteases), siderophores, volatile organic and inorganic compounds, salicylic acid, and N-acyl-homoserine lactones. The higher expression of chitinase (chiA) and genes involved in the biosynthesis of hydrogen cyanide (hcnC), enterobactin (entB), and acetoin (budA) in bacteria exposed to fungal filtrates confirmed that these factors could act in combination, leading to a synergistic inhibitory effect of the strain against phytopathogens. We also confirm the active movement, self-aggregation, exopolysaccharide production, and biofilm formation abilities of the KP32 strain, which are essential for effective plant colonization. Its biological activity and colonization potential indicate that KP32 holds tremendous potential for use as an active biopesticide and plant growth promoter.

Genome sequence of the entomopathogenic Serratia entomophila isolate 626 and characterisation of the species specific itaconate degradation pathway.

BACKGROUND: Isolates of Serratia entomophila and S. proteamaculans (Yersiniaceae) cause disease specific to the endemic New Zealand pasture pest, Costelytra giveni (Coleoptera: Scarabaeidae). Previous genomic profiling has shown that S. entomophila isolates appear to have conserved genomes and, where present, conserved plasmids. In the absence of C. giveni larvae, S. entomophila prevalence reduces in the soil over time, suggesting that S. entomophila has formed a host-specific relationship with C. giveni. To help define potential genetic mechanisms driving retention of the chronic disease of S. entomophila, the genome of the isolate 626 was sequenced, enabling the identification of unique chromosomal properties, and defining the gain/loss of accessory virulence factors relevant to pathogenicity to C. giveni larvae. RESULTS: We report the complete sequence of S. entomophila isolate 626, a causal agent of amber disease in C. giveni larvae. The genome of S. entomophila 626 is 5,046,461 bp, with 59.1% G + C content and encoding 4,695 predicted CDS. Comparative analysis with five previously sequenced Serratia species, S. proteamaculans 336X, S. marcescens Db11, S. nematodiphila DH-S01, S. grimesii BXF1, and S. ficaria NBRC 102596, revealed a core of 1,165 genes shared. Further comparisons between S. entomophila 626 and S. proteamaculans 336X revealed fewer predicted phage-like regions and genomic islands in 626, suggesting less horizontally acquired genetic material. Genomic analyses revealed the presence of a four-gene itaconate operon, sharing a similar gene order as the Yersinia pestis ripABC complex. Assessment of a constructed 626::RipC mutant revealed that the operon confer a possible metabolic advantage to S. entomophila in the initial stages of C. giveni infection. CONCLUSIONS: Evidence is presented where, relative to S. proteamaculans 336X, S. entomophila 626 encodes fewer genomic islands and phages, alluding to limited horizontal gene transfer in S. entomophila. Bioassay assessments of a S. entomophila-mutant with a targeted mutation of the itaconate degradation region unique to this species, found the mutant to have a reduced capacity to replicate post challenge of the C. giveni larval host, implicating the itaconate operon in establishment within the host.