Isolation and molecular characterization of genetically diverse antagonistic, diazotrophic red-pigmented vibrios from different mangrove rhizospheres

Habitat variations of sediment microbial community structure and functions and the influential environmental factors in a Ramsar protected wetland in South China

Ecological functions of coastal wetlands are closely linked to microbiome that is affected by anthropogenic pollution, but related systematic research is rare. This study explored microbial community and physicochemical characteristics of sediments in three habitats, mudflat, mangrove and inter-tidal shrimp ponds (gei wai), in a Ramsar using 16S amplicon sequencing. Proteobacteria was the most abundant and Vibrio was detected in all habitats. Microbial diversity in mangrove is higher than mudflat, with gei wai in between. Microbial functions predicted by PICRUSt revealed prevalence of carbohydrate and amino acid metabolism, with enrichment of nitrogen metabolism in mangrove habitat. Gene annotation identified approximately 800 intrinsic antibiotic resistance genes (iARGs) and dominant mechanism was antibiotic inactivation. Variation partitioning analysis indicated sediment characteristics together with antibiotics and heavy metals shaped microbiomes and iARGs composition in sediments. This study offers insights into variations of sediment microbial diversity, function and iARGs among different habitats in protected wetlands.

Thiophanate-methyl and its major metabolite carbendazim weaken rhizobacteria-mediated defense responses in cucumbers against Fusarium wilt

The effect of fungicides on the plant-rhizosphere microbiome is a subject of ongoing debate, but whether any alteration in the rhizosphere microbiome could affect plant health is an issue that has not been thoroughly investigated. To address this deficiency, we analyzed the rhizosphere microbiome of wilt disease-resistant and disease-susceptible cucumber cultivars to determine whether (and which) plant-associated microorganisms have a role in disease resistance. We further assessed whether the fungicides thiophanate-methyl and carbendazim affect the rhizosphere microbiome, which may contribute to the plant's immune response. Based on results acquired with both radicle-inoculation and soil-inoculation methods, cultivars Longyuanxiuchun (LYXC) and Shuyan2 (SY2) were identified as being disease resistant, whereas Zhongnong6 (ZN6) and Zhongnong38 (ZN38) were susceptible. The microbiome structure differed substantially between the resistant and susceptible plants, with LYXC and SY2 each having a significantly greater Shannon index than Zhongnong38. These results revealed that the disease-resistant cucumber cultivars recruited more beneficial bacteria, i.e., Bacillus, in their rhizosphere soil; as such, Bacillus was identified as a keystone genus in the microbial co-occurrence network. Thus, the presence of Bacillus may help cucumbers defend against fungal pathogens within the rhizosphere. Bacillus subtilis strain LD15, which was isolated from LYXC rhizosphere soil, could suppress pathogen growth, in vitro, and reduce disease severity in pot assays. Moreover, evidence also confirmed the accumulation of LD1 in the rhizosphere soil of resistant cucumber cultivars. For LYXC, application of thiophanate-methyl or carbendazim altered the microbiome structure, decreased bacterial diversity, and reduced the abundance of Bacillus species. Finally, pot assays verified that fungicide application decreased the proportion of LD15 in rhizosphere soil. From a microbial perspective, thiophanate-methyl and carbendazim may weaken the rhizobacteria-mediated defense response of cucumbers against cucumber Fusarium wilt disease. Our findings reveal a role for the rhizosphere microbiome in protecting plants from pathogens and constitute a reference for assessing the ecotoxicological risk of pesticides to non-target soil microorganisms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-024-00181-5.

Investigating dynamics, etiology, pathology, and therapeutic interventions of Caligus clemensi and Vibrio alginolyticus co-infection in farmed marine fish

This study investigated a disease outbreak characterized by caligid copepod infestations and subsequent secondary bacterial infections in European seabass (Dicentrarchus labrax) and flathead grey mullet (Mugil cephalus) cultivated at a private facility in the Deeba Triangle region of Egypt. Moribund fish displayed brown spots on the skin, tongue, and gills, along with lethargy and excess mucus. The fish suffered severe infections, exhibiting external hemorrhages, ulcers, and ascites. The fish had pale, enlarged livers with hemorrhaging. Comprehensive parasitological, bacteriological, molecular, immunity and histopathological analyses were conducted to identify the etiological agents and pathological changes. Caligid copepod infestation was observed in wet mounts from the buccal and branchial cavities of all examined fish, and the caligids were identified as Caligus clemensi through COI gene sequencing and phylogenetic analysis. Vibrio alginolyticus was confirmed as a secondary bacterial infection through biochemical tests, recA gene sequencing, and phylogenetic analyses. Antibiotic susceptibility testing revealed resistance to β-lactams, aminoglycosides, and trimethoprim-sulfamethoxazole in V. alginolyticus isolates. Upregulation of the inflammatory marker IL-1β in gill and skin tissues indicated a robust cell-mediated immune response against the pathogens. Histopathological examination revealed severe tissue damage, hyperplasia, hemorrhage, and congestion in the gills, along with hepatocellular degeneration and steatosis in the liver, providing initial insights into this outbreak. A comprehensive therapeutic regimen was implemented, comprising prolonged hydrogen peroxide immersion baths, followed by the application of the nature-identical plant-based compound Lice-less and probiotic Sanolife Pro-W supplementation. This integrated approach effectively eliminated C. clemensi infestations, controlled secondary bacterial infections, and restored fish health, reducing morbidity and mortality rates to minimal levels.

A Redox-Regulated, Heterodimeric NADH:cinnamate Reductase in Vibrio ruber

Genes of putative reductases of α,β-unsaturated carboxylic acids are abundant among anaerobic and facultatively anaerobic microorganisms, yet substrate specificity has been experimentally verified for few encoded proteins. Here, we co-produced in Escherichia coli a heterodimeric protein of the facultatively anaerobic marine bacterium Vibrio ruber (GenBank SJN56019 and SJN56021; annotated as NADPH azoreductase and urocanate reductase, respectively) with Vibrio cholerae flavin transferase. The isolated protein (named Crd) consists of the sjn56021-encoded subunit CrdB (NADH:flavin, FAD binding 2, and FMN bind domains) and an additional subunit CrdA (SJN56019, a single NADH:flavin domain) that interact via their NADH:flavin domains (Alphafold2 prediction). Each domain contains a flavin group (three FMNs and one FAD in total), one of the FMN groups being linked covalently by the flavin transferase. Crd readily reduces cinnamate, p-coumarate, caffeate, and ferulate under anaerobic conditions with NADH or methyl viologen as the electron donor, is moderately active against acrylate and practically inactive against urocanate and fumarate. Cinnamates induced Crd synthesis in V. ruber cells grown aerobically or anaerobically. The Crd-catalyzed reduction started by NADH demonstrated a time lag of several minutes, suggesting a redox regulation of the enzyme activity. The oxidized enzyme is inactive, which apparently prevents production of reactive oxygen species under aerobic conditions. Our findings identify Crd as a regulated NADH-dependent cinnamate reductase, apparently protecting V. ruber from (hydroxy)cinnamate poisoning.

Agricultural Jiaosu: An Eco-Friendly and Cost-Effective Control Strategy for Suppressing Fusarium Root Rot Disease in Astragalus membranaceus

Root rot caused by the pathogenic fungi of the Fusarium genus poses a great threat to the yield and quality of medicinal plants. The application of Agricultural Jiaosu (AJ), which contains beneficial microbes and metabolites, represents a promising disease control strategy. However, the action-effect of AJ on Fusarium root rot disease remains unclear. In the present study, we evaluated the characteristics and antifungal activity of AJ fermented using waste leaves and stems of medicinal plants, and elucidated the mechanisms of AJ action by quantitative real-time PCR and redundancy analysis. The effects of AJ and antagonistic microbes isolated from it on disease suppression were further validated through a pot experiment. Our results indicate that the AJ was rich in beneficial microorganisms (Bacillus, Pseudomonas, and Lactobacillus), organic acids (acetic, formic, and butyric acids) and volatile organic compounds (alcohols and esters). It could effectively inhibit Fusarium oxysporum and the half-maximal inhibitory concentration (IC₅₀) was 13.64%. The antifungal contribution rate of the microbial components of AJ reached 46.48%. Notably, the redundancy analysis revealed that the Bacillus and Pseudomonas genera occupied the main niche during the whole inhibition process. Moreover, the abundance of the Bacillus, Pseudomonas, and Lactobacillus genera were positively correlated with the pH-value, lactic, formic and butyric acids. The results showed that the combined effects of beneficial microbes and organic acid metabolites increased the efficacy of the AJ antifungal activity. The isolation and identification of AJ’s antagonistic microbes detected 47 isolates that exhibited antagonistic activities against F. oxysporum in vitro. In particular, Bacillus subtilis and Bacillus velezensis presented the strongest antifungal activity. In the pot experiment, the application of AJ and these two Bacillus species significantly reduced the disease incidence of Fusarium root rot and promoted the growth of Astragalus. The present study provides a cost-effective method to control of Fusarium root rot disease, and establishes a whole-plant recycling pattern to promote the sustainable development of medicinal plant cultivation.

Bacillus subtilis BR4 derived stigmatellin Y interferes Pqs-PqsR mediated quorum sensing system of Pseudomonas aeruginosa

Cell-to-cell communication is essentially required in bacteria for the production of multiple virulence factors and successful colonization in the host. Targeting the virulence factors production without hampering the growth of the pathogens is a potential strategy to control pathogenesis. To accomplish this, a total of 43 mangrove isolates were screened for quorum quenching (QQ) activity against Pseudomonas aeruginosa (PA), in which eight bacteria have shown antibiofilm activity without hampering the growth of the PA. Prominent QQ activity was observed in Bacillus subtilis BR4. Previously, we found that BR4 produces stigmatellin Y, a structural analogue of PQS signal of PA, which could competitively bind with PqsR receptor and inhibits the quorum sensing (QS) system of PA. Further, stigmatellin Y containing ethyl acetate extract (S-EAE) (100 µg ml^-1 ) of BR4 significantly inhibits (p < 0.001) the biofilm formation of PA. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) analysis also fortified the QQ activity of BR4. Furthermore, S-EAE of BR4 (500 µg ml^-1 ) has significantly reduced the production of virulence factors, including protease, elastase, pyocyanin and extracellular polysaccharides substances. Furthermore, liquid chromatography-mass spectrometry (LC-MS)/MS analysis affirms that BR4 intercepts the PQS-mediated QS system by reducing the synthesis of as many PQS signals, including precursor molecule (243.162313 Da) of PQS signal. Thus, S-EAE of B. subtilis BR4 could be used as a promising therapeutic agent to combat QS system-mediated pathogenesis of PA. Further therapeutic potentials of stigmatellin Y to be evaluated in clinical studies for the treatment of multidrug resistant PA.

Genetic Elucidation of Quorum Sensing and Cobamide Biosynthesis in Divergent Bacterial-Fungal Associations Across the Soil-Mangrove Root Interface

Plant roots in soil host a repertoire of bacteria and fungi, whose ecological interactions could improve their functions and plant performance. However, the potential microbial interactions and underlying mechanisms remain largely unknown across the soil-mangrove root interface. We herein analyzed microbial intra- and inter-domain network topologies, keystone taxa, and interaction-related genes across four compartments (non-rhizosphere, rhizosphere, episphere, and endosphere) from a soil-mangrove root continuum, using amplicon and metagenome sequencing technologies. We found that both intra- and inter-domain networks displayed notable differences in the structure and topology across four compartments. Compared to three peripheral compartments, the endosphere was a distinctive compartment harboring more dense co-occurrences with a higher average connectivity in bacterial-fungal network (2.986) than in bacterial (2.628) or fungal network (2.419), which could be related to three bacterial keystone taxa (Vibrio, Anaerolineae, and Desulfarculaceae) detected in the endosphere as they are known to intensify inter-domain associations with fungi and stimulate biofilm formation. In support of this finding, we also found that the genes involved in cell-cell communications by quorum sensing (rhlI, lasI, pqsH, and lasR) and aerobic cobamide biosynthesis (cobG, cobF, and cobA) were highly enriched in the endosphere, whereas anaerobic cobamide biosynthesis (encoded by cbiT and cbiE) was dominant in three peripheral compartments. Our results provide genetic evidence for the intensified bacterial-fungal associations of root endophytes, highlighting the critical role of the soil-root interface in structuring the microbial inter-domain associations.

Isolation and characterization of antagonistic Paenibacillus polymyxa HX-140 and its biocontrol potential against Fusarium wilt of cucumber seedlings

Objective

The aim of this study is to evaluate the efficacy of the strain Paenibacillus polymyxa HX-140, isolated from the rhizosphere soil of rape, to control Fusarium wilt of cucumber seedlings caused by Fusarium oxysporum f. sp. cucumerinum.

Results

Strain HX-140 was able to produce protease, cellulase, β-1,3-glucanase and antifungal volatile organic compounds. An in vitro dual culture test showed that strain HX-140 exhibited broad spectrum antifungal activity against soil-borne plant pathogenic fungi. Strain HX-140 also reduced the infection of Fusarium wilt of cucumber seedlings by 55.6% in a greenhouse pot experiment. A field plot experiment confirmed the biocontrol effects and further revealed that antifungal activity was positively correlated with inoculum size by the root-irrigation method. Here, inoculums at 10⁶ 10⁷ and 10⁸ cfu/mL of HX-140 bacterial suspension reduced the incidence of Fusarium wilt of cucumber seedling by 19.5, 41.1, and 50.9%, respectively.

Conclusions

Taken together, our results suggest that P. polymyxa HX-140 has significant potential in the control of Fusarium wilt and possibly other fungal diseases of cucumber.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02131-3.

Life from the ashes: survival of dry bacterial spores after very high temperature exposure

We found that spores of Bacillus amyloliquefaciens rank amongst the most resistant to high temperatures with a maximum dry heat tolerance determined at 420 °C. We found that this extreme heat resistance was also maintained after several generations suggesting that the DNA was able to replicate after exposure to these temperatures. Nonetheless, amplifying the bacterial DNA using BOXA1R and (GTG)₅ primers was unsuccessful immediately after extreme heating, but was successful after incubation of the heated then cooled spores. Moreover, enzymes such as amylases and proteases were active directly after heating and spore regeneration, indicating that DNA coding for these enzymes were not degraded at these temperatures. Our results suggest that extensive DNA damage may occur in spores of B. amyloliquefaciens directly after an extreme heat shock. However, the successful germination of spores after inoculation and incubation indicates that these spores could have a very effective DNA repair mechanism, most likely protein-based, able to function after exposure to temperatures up to 420 °C. Therefore, we propose that B. amyloliquefaciens is one of the most heat resistant life forms known to science and can be used as a model organism for studying heat resistance and DNA repair. Furthermore, the extremely high temperature resistivity of these spores has exceptional consequences for general methodology, such as the use of dry heat sterilization and, therefore, virtually all studies in the broad area of high temperature biology.

Arthrobacter pokkalii sp nov, a Novel Plant Associated Actinobacterium with Plant Beneficial Properties, Isolated from Saline Tolerant Pokkali Rice, Kerala, India

A novel yellow colony-forming bacterium, strain P3B162T was isolated from the pokkali rice rhizosphere from Kerala, India, as part of a project study aimed at isolating plant growth beneficial rhizobacteria from saline tolerant pokkali rice and functionally evaluate their abilities to promote plant growth under saline conditions. The novel strain P3B162T possesses plant growth beneficial traits such as positive growth on 1-aminocyclopropane-1-carboxylic acid (ACC), production of indole acetic acid (IAA) and siderophore. In addition, it also showed important phenotypic characters such as ability to form biofilm and utilization of various components of plant root exudates (sugars, amino acids and organic acids), clearly indicating its lifestyle as a plant rhizosphere associated bacterium. Taxonomically, the novel strain P3B162T was affiliated to the genus Arthrobacter based on the collective results of phenotypic, genotypic and chemotaxonomic analyses. Moreover, molecular analysis using 16S rRNA gene showed Arthrobacter globiformis NBRC 12137T, Arthrobacter pascens DSM 20545T and Arthrobacter liuii DSXY973T as the closely related phylogenetic neighbours, showing more than 98% 16S rRNA similarity values, whereas the recA gene analysis displayed Arthrobacter liuii JCM 19864T as the nearest neighbour with 94.7% sequence similarity and only 91.7% to Arthrobacter globiformis LMG 3813T and 88.7% to Arthrobacter pascens LMG 16255T. However, the DNA-DNA hybridization values between strain P3B162T, Arthrobacter globiformis LMG 3813T, Arthrobacter pascens LMG 16255T and Arthrobacter liuii JCM 19864T was below 50%. In addition, the novel strain P3B162T can be distinguished from its closely related type strains by several phenotypic characters such as colony pigment, tolerance to NaCl, motility, reduction of nitrate, hydrolysis of DNA, acid from sucrose, cell wall sugars and cell wall peptidoglycan structure. In conclusion, the combined results of this study support the classification of strain P3B162T as a novel Arthrobacter species and we propose Arthrobacter pokkalii sp.nov.as its name. The type strain is P3B162T (= KCTC 29498T = MTCC 12358T).

Description of Vogesella oryzae sp. nov., isolated from the rhizosphere of saline tolerant pokkali rice

Three strains, namely L3B39(T), L3D16, and L1E9, were obtained while studying the cultivable rhizosphere bacteria of saline tolerant pokkali rice, at Kerala, India. The novel strains were negative for many plant growth promoting plate assays such as phytohormone and siderophore production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase and growth in nitrogen free agar medium but found to utilize malic acid, citrate, D-glucose, L-arabinose, and D-maltose, important components of the plant root exudates, indicating that they are normal plant rhizosphere residents without yet known benefits to the plant. The 16S rRNA gene analysis placed these strains in the genus Vogesella, forming a separate branch independent of the previously described type strains of this genus in all tree making algorithms applied. Vogesella perlucida DS-28(T) was the type strain with highest 16S rRNA sequence similarity (97.59%). DNA-DNA hybridization values among these novel strains were above 85% andthat with Vogesella perlucida LMG 24214(T) was below 50%. Phenotypically, the novel strains can be differentiated from Vogesella perlucida LMG 24214(T) by many characters such as NaCl tolerance, growth temperature, and utilization of L-arabinose, D-maltose, and citrate. These novel strains contain C16:1ω6c/C16:1ω7c and C16:0 as major fatty acids, ubiquinone Q-8 as the major respiratory quinone, and phosphatidylethanolamine and phosphatidylglycerol as major polar lipids. Based on the results obtained from the polyphasic taxonomic approach we conclude that the strains belong to a novel Vogesella species for which the name Vogesella oryzae sp.nov. is proposed. The type strain is L3B39(T) (= LMG 28272(T)=DSM 28780(T)).

Anthropogenic impact on diazotrophic diversity in the mangrove rhizosphere revealed by nifH pyrosequencing

Diazotrophs in the mangrove rhizosphere play a major role in providing new nitrogen to the mangrove ecosystem and their composition and activity are strongly influenced by anthropogenic activity and ecological conditions. In this study, the diversity of the diazotroph communities in the rhizosphere sediment of five tropical mangrove sites with different levels of pollution along the north and south coastline of Singapore were studied by pyrosequencing of the nifH gene. Bioinformatics analysis revealed that in all the studied locations, the diazotroph communities comprised mainly of members of the diazotrophic cluster I and cluster III. The detected cluster III diazotrophs, which were composed entirely of sulfate-reducing bacteria, were more abundant in the less polluted locations. The metabolic capacities of these diazotrophs indicate the potential for bioremediation and resiliency of the ecosystem to anthropogenic impact. In heavily polluted locations, the diazotrophic community structures were markedly different and the diversity of species was significantly reduced when compared with those in a pristine location. This, together with the increased abundance of Marinobacterium, which is a bioindicator of pollution, suggests that anthropogenic activity has a negative impact on the genetic diversity of diazotrophs in the mangrove rhizosphere.

Vibrio oceanisediminis sp. nov., a nitrogen-fixing bacterium isolated from an artificial oil-spill marine sediment

A Gram-staining-negative, halophilic, facultatively anaerobic, motile, rod-shaped and nitrogen-fixing bacterium, designated strain S37T, was isolated from an artificial oil-spill sediment sample from the coast of Taean, South Korea. Cells grew at 10–37 °C and pH 5.0–9.0, with optimal growth at 28 °C and pH 6.0–8.0. Growth was observed with 1–9 % (w/v) NaCl in marine broth, with optimal growth with 3–5 % NaCl, but no growth was observed in the absence of NaCl. According to the results of 16S rRNA gene sequence analysis, strain S37T represents a member of the genus Vibrio of the class Gammaproteobacteria and forms a clade with Vibrio plantisponsor MSSRF60T (97.38 %), Vibrio diazotrophicus ATCC 33466T (97.31 %), Vibrio aestuarianus ATCC 35048T (97.07 %) Vibrio areninigrae J74T (96.76 %) and Vibrio hispanicus LMG 13240T (96.76 %). The major fatty acids were C16 : 0, C16 : 1ω7c/C16 : 1ω6c and C18 : 1ω7c/C18 : 1ω6c. The DNA G+C content was 41.9 %. The DNA–DNA hybridization analysis results showed a 30.2 % association value with the closely related type strain V. plantisponsor DSM 21026T. On the basis of phenotypic and chemotaxonomic characteristics, strain S37T represents a novel species of the genus Vibrio, for which the name Vibrio oceanisediminis sp. nov., is proposed with the type strain S37T ( = KEMB 2255-005T = JCM 30409T).

Application of a new xylanase activity from Bacillus amyloliquefaciens XR44A in brewer's spent grain saccharification

BACKGROUND

Cellulases and xylanases are the key enzymes involved in the conversion of lignocelluloses into fermentable sugars. Western Ghat region (India) has been recognized as an active hot spot for the isolation of new microorganisms. The aim of this work was to isolate new microorganisms producing cellulases and xylanases to be applied in brewer's spent grain saccharification.

RESULTS

93 microorganisms were isolated from Western Ghat and screened for the production of cellulase and xylanase activities. Fourteen cellulolytic and seven xylanolytic microorganisms were further screened in liquid culture. Particular attention was focused on the new isolate Bacillus amyloliquefaciens XR44A, producing xylanase activity up to 10.5 U mL^-1. A novel endo-1,4-beta xylanase was identified combining zymography and proteomics and recognized as the main enzyme responsible for B. amyloliquefaciens XR44A xylanase activity. The new xylanase activity was partially characterized and its application in saccharification of brewer's spent grain, pretreated by aqueous ammonia soaking, was investigated.

CONCLUSION

The culture supernatant of B. amyloliquefaciens XR44A with xylanase activity allowed a recovery of around 43% xylose during brewer's spent grain saccharification, similar to the value obtained with a commercial xylanase from Trichoderma viride, and a maximum arabinose yield of 92%, around 2-fold higher than that achieved with the commercial xylanase. © 2014 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Novel Phl-producing genotypes of finger millet rhizosphere associated pseudomonads and assessment of their functional and genetic diversity

Genetic diversity of phlD gene, an essential gene in the biosynthesis of 2,4-diacetylphloroglucinol, was studied by restriction fragment length polymorphism (RFLP) in 20 Phl-producing pseudomonads isolated from finger millet rhizosphere. RFLP analysis of phlD gene displayed three patterns with HaeIII and TaqI enzymes. phlD gene sequence closely correlated with RFLP results and revealed the existence of three new genotypes G, H and I. Further, the phylogenetic and concatenated sequence analysis of the 16S rRNA, rpoB, gyrB, rpoD genes supported the hypothesis that these genotypes G, H and I were different from reported genotypes A-F. In all phylogenetic studies, the genotype G formed a distant clade from the groups of Pseudomonas putida and P. aeruginosa (sensu strictu), but the groups H and I were closely related to P. aeruginosa/P. stutzeri group. The Phl-producing pseudomonads exhibited antagonistic activity against Pyricularia grisea (TN508), Gaeumannomyces graminis (DSM1463), Fusarium oxysporum (DSM62297), Xanthomonas campestris (DSM3586) and Erwinia persicina (HMGU155). In addition, these strains exhibited various plant growth-promoting traits. In conclusion, this study displays the existence of novel Phl-producing pseudomonads genotypes G, H and I from finger millet rhizosphere, which formed taxonomically outward phylogenetic lineage from the groups of P. putida and P. aeruginosa (sensu strictu).

Zunongwangia mangrovi sp. nov., isolated from mangrove (Avicennia marina) rhizosphere, and emended description of the genus Zunongwangia

A Gram-stain-negative, strictly aerobic, slightly halophilic, non-motile and rod-shaped bacterial strain, designated P2E16T, was isolated from mangrove (Avicennia marina) rhizosphere, collected at Devipattinam mangroves, Tamil Nadu, India. Strain P2E16T grew optimally at pH 7.0–8.0, at 25–28 °C and in the presence of 2–3 % (w/v) NaCl. 16S rRNA gene analysis showed that strain P2E16T was phylogenetically closely related to the genus Zunongwangia , with Zunongwangia profunda SM-A87T as the closest related type strain (98.2 % 16S rRNA gene sequence similarity) and less than 93 % 16S rRNA gene sequence similarity to all other members of the family Flavobacteriaceae . Strain P2E16T contained MK-6 as the major respiratory quinone, phosphatidylethanolamine as the predominant polar lipid and iso-C15 : 0 (17.8 %), iso-C17 : 0 3-OH (15.1 %), C15 : 0 (12.8 %), iso-C17 : 1ω9c (9.8 %), iso-C15 : 1 G (9.0 %), and summed feature 3 (comprising C16 : 1ω7c and/or iso-C15 : 0 2-OH; 7.1 %) as the major fatty acids. The DNA G+C content was 34.3 mol%. Differential phenotypic properties, together with the phylogenetic distinctiveness and low DNA–DNA relatedness demonstrated that strain P2E16T was distinct from the type strain of Zunongwangia profunda . On the basis of these presented data, strain P2E16T is considered to represent a novel species of the genus Zunongwangia , for which the name Zunongwangia mangrovi sp. nov. is proposed. The type strain is P2E16T ( = DSM 24499T = LMG 26237T = KCTC 23496T). An emended description of the genus Zunongwangia is also provided.

Ciceribacter lividus gen. nov., sp. nov., isolated from rhizosphere soil of chick pea (Cicer arietinum L.)

The taxonomic position of strain MSSRFBL1(T), isolated from chickpea rhizosphere soil from Kannivadi, India, was determined. Strain MSSRFBL1(T) formed bluish black colonies, stained Gram-negative and was motile, aerobic, capable of fixing dinitrogen, oxidase-negative and catalase-positive. Q-10 was the major respiratory quinone. Major fatty acids of strain MSSRFBL1(T) were C18 : 1ω7c and C19 : 0cycloω8c. Minor amounts of C18 : 0, C12 : 0, C14 : 0 3-OH, C18 : 0 3-OH, C16 : 0, C16 : 1ω6c/C16 : 1ω7c, C17 : 0 3-OH and C20 : 1ω7c were also present. Polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylcholine and two unidentified glycolipids. Bacteriohopane derivatives (BHD1 and 2), diplopterol, diploptene, bishomohopanediol, adenosylhopane and 2β-methyl bacteriohopanetetrol were the major hopanoids of strain MSSRFBL1(T). The genomic DNA G+C content was 71 mol%. EzTaxon-e-based blast analysis of the 16S rRNA gene indicated the highest similarity of strain MSSRFBL1(T) to Ensifer adhaerens LMG 20216(T) (97.3 %) and other members of the genus Ensifer (<96.9 %) in the family Rhizobiaceae of the class Alphaproteobacteria. However, phylogenetic analysis based on 16S rRNA, recA, thrC and dnaK gene sequences showed distinct out-grouping from the recognized genera of the family Rhizobiaceae. Based on phenotypic, genotypic and chemotaxonomic characters, strain MSSRFBL1(T) represents a novel species in a new genus in the family Rhizobiaceae for which the name Ciceribacter lividus gen. nov., sp. nov. is proposed. The type strain of Ciceribacter lividus is MSSRFBL1(T) ( = DSM 25528(T) = KCTC 32403(T)).

Alleviation of fungicide-induced phytotoxicity in greengram [Vigna radiata (L.) Wilczek] using fungicide-tolerant and plant growth promoting Pseudomonas strain

This study was designed to explore beneficial plant-associated rhizobacteria exhibiting substantial tolerance against fungicide tebuconazole vis-à-vis synthesizing plant growth regulators under fungicide stressed soils and to evaluate further these multifaceted rhizobacteria for protection and growth promotion of greengram [Vigna radiata (L.) Wilczek] plants against phytotoxicity of tebuconazole. Tebuconazole-tolerant and plant growth promoting bacterial strain PS1 was isolated from mustard (Brassica compestris) rhizosphere and identified as Pseudomonas aeruginosa following 16S rRNA gene sequencing. The P. aeruginosa strain PS1 solubilized phosphate significantly and produced indole acetic acid, siderophores, exo-polysaccharides, hydrogen cyanide and ammonia even under tebuconazole stress. Generally, tebuconazole at the recommended, two and three times the recommended field rate adversely affected the growth, symbiosis, grain yield and nutrient uptake in greengram in a concentration dependent manner. In contrast, the P. aeruginosa strain PS1 along with tebuconazole significantly, increased the growth parameters of the greengram plants. The inoculant strain PS1 increased appreciably root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, and seed yield of greengram plants at all tested concentrations of tebuconazole when compared to the uninoculated plants treated with tebuconazole. The results suggested that the P. aeruginosa strain PS1, exhibiting novel plant growth regulating physiological features, can be applied as an eco-friendly and plant growth catalyzing bio-inoculant to ameliorate the performance of greengram in fungicide stressed soils.

Mangrove bacterial richness

Mangroves are complex and dynamic ecosystems varying in salinity, water level and nutrient availability; they also contain diverse and distinct microbial communities. Studies of microbes and their interactions with other ecosystem components (e.g., tree roots) are critical for our understanding of mangrove ecosystem functioning and remediation. Using a barcoding pyrosequencing approach, we previously noted the persistence of terrestrial bacterial populations on mangrove roots when nursery raised saplings were transplanted back to their natural environment. Here we go into further detail about the potential functional associations of bacterial guilds with distinct mangrove microhabitats including the rhizosphere. We also use a nonparametric richness estimator to show that estimated operational taxonomic unit (OTU) richness is more than twice that observed. In the transplant microhabitat, our estimate suggests that there are almost 7,000 OTU's for a sample size of 10,400 individual sequences with no sign of an asymptote, indicating that "true" richness for this microhabitat is substantially larger. Results on the number of bacterial OTU's should, however, be viewed with caution given that the barcoding pyrosequencing technique used can yield sequencing artifacts that may inflate richness estimates if not properly removed.

Vibrio plantisponsor sp. nov., a diazotrophic bacterium isolated from a mangrove associated wild rice (Porteresia coarctata Tateoka)

Two Gram negative, facultatively anaerobic, halophilic, motile, slightly curved rod-shaped bacterial strains MSSRF60(T) and MSSRF64 were isolated from the roots of a mangrove-associated wild rice collected in the Pichavaram mangroves, India. These strains possess the key functional nitrogenase gene nifH. Phylogenetic analysis based on the 16S rRNA, recA, gapA, mreB, gyrB and pyrH, gene sequences revealed that strains MSSRF60(T) and MSSRF64 belong to the genus Vibrio, and had the highest sequence similarity with the type strains of Vibrio diazotrophicus LMG 7893(T) (99.7, 94.8, 98.5, 97.9, 94.0 and 90.7%, respectively), Vibrio areninigrae J74(T) (98.2, 87.5, 91.5, 88.9, 86.5 and 84.6% respectively) and Vibrio hispanicus LMG 13240(T) (97.8, 87.1, 91.7, 89.8, 84.1 and 81.9%, respectively). The fatty acid composition too confirmed the affiliation of strains MSSRF60(T) and MSSRF64 to the genus Vibrio. These strains can be differentiated from the most closely related Vibrio species by several phenotypic traits. The DNA G+C content of strain MSSRF60(T) was 41.8mol%. Based on phenotypic, chemotaxonomic, genotypic (multilocus sequence analysis using five genes and genomic fingerprinting using BOX-PCR) and DNA-DNA hybridization analyses, strains MSSRF60(T) and MSSRF64 represent a novel species of the genus Vibrio, for which the name Vibrio plantipsonsor sp. nov. is proposed. The type strain is MSSRF60(T) (=DSM 21026(T)=LMG 24470(T)=CAIM 1392(T)).