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Frontiers in Microbiology 2020Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress....
Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress. In this study, 21 (26.9%) rhizobacterial strains isolated from drought-prone ecosystems of Bangladesh were able to form air-liquid (AL) biofilms in the glass test tubes containing salt-optimized broth plus glycerol (SOBG) medium. Based on 16S rRNA gene sequencing, (ESR3 and ESR15), ESR4, ESR6, (ESR7 and ESR25), ESR9, (ESR12, ESR16, and ESR23), (ESR13 and ESR21), ESB18, ESR20, (ESD3, ESD21, and ESB22), ESD16, ESB6, ESB9, and ESD8 were identified. Fourier transform infrared spectroscopy studies showed that the biofilm matrices contain proteins, polysaccharides, nucleic acids, and lipids. Congo red binding results indicated that these bacteria produced curli fimbriae and nanocellulose-rich polysaccharides. Expression of nanocellulose was also confirmed by Calcofluor binding assays and scanning electron microscopy. studies revealed that all these rhizobacterial strains expressed multiple plant growth-promoting traits including N fixation, production of indole-3-acetic acid, solubilization of nutrients (P, K, and Zn), and production of ammonia, siderophores, ACC deaminase, catalases, lipases, cellulases, and proteases. Several bacteria were also tolerant to multifarious stresses such as drought, high temperature, extreme pH, and salinity. Among these rhizobacteria, ESR12, ESR15, and ESD3 impeded the growth of pv. ATCC 33913, while ESR15 and ESD21 prevented the progression of ATCC 11696. In a pot experiment, tomato plants inoculated with ESR4, ESR6, ESR9, ESR12, ESR15, ESR20, ESR21, and ESB6 exhibited an increased plant growth compared to the non-inoculated plants under water deficit-stressed conditions. Accordingly, the bacterial-treated plants showed a higher antioxidant defense system and a fewer tissue damages than non-inoculated plants under water-limiting conditions. Therefore, biofilm-producing PGPR can be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress.
PubMed: 33324354
DOI: 10.3389/fmicb.2020.542053 -
Microbial Biotechnology Mar 2023Mediated extracellular electron transfer (EET) might be a great vehicle to connect microbial bioprocesses with electrochemical control in stirred-tank bioreactors....
Mediated extracellular electron transfer (EET) might be a great vehicle to connect microbial bioprocesses with electrochemical control in stirred-tank bioreactors. However, mediated electron transfer to date is not only much less efficient but also much less studied than microbial direct electron transfer to an anode. For example, despite the widespread capacity of pseudomonads to produce phenazine natural products, only Pseudomonas aeruginosa has been studied for its use of phenazines in bioelectrochemical applications. To provide a deeper understanding of the ecological potential for the bioelectrochemical exploitation of phenazines, we here investigated the potential electroactivity of over 100 putative diverse native phenazine producers and the performance within bioelectrochemical systems. Five species from the genera Pseudomonas, Streptomyces, Nocardiopsis, Brevibacterium and Burkholderia were identified as new electroactive bacteria. Electron discharge to the anode and electric current production correlated with the phenazine synthesis of Pseudomonas chlororaphis subsp. aurantiaca. Phenazine-1-carboxylic acid was the dominant molecule with a concentration of 86.1 μg/ml mediating an anodic current of 15.1 μA/cm . On the other hand, Nocardiopsis chromatogenes used a wider range of phenazines at low concentrations and likely yet-unknown redox compounds to mediate EET, achieving an anodic current of 9.5 μA/cm . Elucidating the energetic and metabolic usage of phenazines in these and other species might contribute to improving electron discharge and respiration. In the long run, this may enhance oxygen-limited bioproduction of value-added compounds based on mediated EET mechanisms.
Topics: Phenazines; Pseudomonas; Oxidation-Reduction
PubMed: 36571174
DOI: 10.1111/1751-7915.14199 -
Microbiome Feb 2020The holistic view of bacterial symbiosis, incorporating both host and microbial environment, constitutes a major conceptual shift in studies deciphering host-microbe...
BACKGROUND
The holistic view of bacterial symbiosis, incorporating both host and microbial environment, constitutes a major conceptual shift in studies deciphering host-microbe interactions. Interactions between Steinernema entomopathogenic nematodes and their bacterial symbionts, Xenorhabdus, have long been considered monoxenic two partner associations responsible for the killing of the insects and therefore widely used in insect pest biocontrol. We investigated this "monoxenic paradigm" by profiling the microbiota of infective juveniles (IJs), the soil-dwelling form responsible for transmitting Steinernema-Xenorhabdus between insect hosts in the parasitic lifecycle.
RESULTS
Multigenic metabarcoding (16S and rpoB markers) showed that the bacterial community associated with laboratory-reared IJs from Steinernema carpocapsae, S. feltiae, S. glaseri and S. weiseri species consisted of several Proteobacteria. The association with Xenorhabdus was never monoxenic. We showed that the laboratory-reared IJs of S. carpocapsae bore a bacterial community composed of the core symbiont (Xenorhabdus nematophila) together with a frequently associated microbiota (FAM) consisting of about a dozen of Proteobacteria (Pseudomonas, Stenotrophomonas, Alcaligenes, Achromobacter, Pseudochrobactrum, Ochrobactrum, Brevundimonas, Deftia, etc.). We validated this set of bacteria by metabarcoding analysis on freshly sampled IJs from natural conditions. We isolated diverse bacterial taxa, validating the profile of the Steinernema FAM. We explored the functions of the FAM members potentially involved in the parasitic lifecycle of Steinernema. Two species, Pseudomonas protegens and P. chlororaphis, displayed entomopathogenic properties suggestive of a role in Steinernema virulence and membership of the Steinernema pathobiome.
CONCLUSIONS
Our study validates a shift from monoxenic paradigm to pathobiome view in the case of the Steinernema ecology. The microbial communities of low complexity associated with EPNs will permit future microbiota manipulation experiments to decipher overall microbiota functioning in the infectious process triggered by EPN in insects and, more generally, in EPN ecology.
Topics: Animals; Biological Control Agents; DNA Barcoding, Taxonomic; Host Microbial Interactions; Larva; Life Cycle Stages; Microbiota; Moths; Proteobacteria; Rhabditida; Rhabditida Infections; Symbiosis; Virulence
PubMed: 32093774
DOI: 10.1186/s40168-020-00800-5 -
Frontiers in Microbiology 2023The jumbo phages encode proteins that assemble to form a nucleus-like compartment in infected cells. Here we report the cryo-EM structure and biochemistry...
The jumbo phages encode proteins that assemble to form a nucleus-like compartment in infected cells. Here we report the cryo-EM structure and biochemistry characterization of gp105, a protein that is encoded by the jumbo phage 201φ2-1 and is involved in the formation of the nucleus-like compartment in phage 201φ2-1 infected . We found that, although most gp105 molecules are in the monomeric state in solution, a small portion of gp105 assemble to form large sheet-like assemblies and small cube-like particles. Reconstruction of the cube-like particles showed that the particle consists of six flat head-to-tail tetramers arranged into an octahedral cube. The four molecules at the contact interface of two head-to-tail tetramers are 2-fold symmetry-related and constitute a concave tetramer. Further reconstructions without applying symmetry showed that molecules in the particles around the distal ends of a 3-fold axis are highly dynamic and have the tendency to open up the assembly. Local classifications and refinements of the concave tetramers in the cube-like particle resulted in a map of the concave tetramer at a resolution of 4.09 Å. Structural analysis of the concave tetramer indicates that the N and C terminal fragments of gp105 are important for mediating the intermolecular interactions, which was further confirmed by mutagenesis studies. Biochemistry assays showed that, in solution, the cube-like particles of gp105 are liable to either disassemble to form the monomers or recruit more molecules to form the high molecular weight lattice-like assembly. We also found that monomeric gp105s can self-assemble to form large sheet-like assemblies , and the assembly of gp105 is a reversible dynamic process and temperature-dependent. Taken together, our results revealed the dynamic assembly of gp105, which helps to understand the development and function of the nucleus-like compartment assembled by phage-encoded proteins.
PubMed: 37138628
DOI: 10.3389/fmicb.2023.1170112 -
Environmental Microbiology Sep 2021Strains belonging to the Pseudomonas protegens and Pseudomonas chlororaphis species are able to control soilborne plant pathogens and to kill pest insects by producing...
Strains belonging to the Pseudomonas protegens and Pseudomonas chlororaphis species are able to control soilborne plant pathogens and to kill pest insects by producing virulence factors such as toxins, chitinases, antimicrobials or two-partner secretion systems. Most insecticidal Pseudomonas described so far were isolated from roots or soil. It is unknown whether these bacteria naturally occur in arthropods and how they interact with them. Therefore, we isolated P. protegens and P. chlororaphis from various healthy insects and myriapods, roots and soil collected in an agricultural field and a neighbouring grassland. The isolates were compared for insect killing, pathogen suppression and host colonization abilities. Our results indicate that neither the origin of isolation nor the phylogenetic position mirror the degree of insecticidal activity. Pseudomonas protegens strains appeared homogeneous regarding phylogeny, biocontrol and insecticidal capabilities, whereas P. chlororaphis strains were phylogenetically and phenotypically more heterogenous. A phenotypic and genomic analysis of five closely related P. chlororaphis isolates displaying varying levels of insecticidal activity revealed variations in genes encoding insecticidal factors that may account for the reduced insecticidal activity of certain isolates. Our findings point towards an adaption to insects within closely related pseudomonads and contribute to understand the ecology of insecticidal Pseudomonas.
Topics: Animals; Arthropods; Genetic Variation; Insecta; Insecticides; Phylogeny
PubMed: 34190383
DOI: 10.1111/1462-2920.15623 -
EFSA Journal. European Food Safety... Oct 2020The European Commission requested EFSA to provide scientific advice on the translocation potential by MA342 in plants after seed treatment of cereals and peas and, if...
The European Commission requested EFSA to provide scientific advice on the translocation potential by MA342 in plants after seed treatment of cereals and peas and, if applicable, for a revision of the assessment of the risk to humans by its metabolite 2,3-deepoxy-2,3-didehydro-rhizoxin (DDR) and this based on the evidence available in the dossier for renewal of the approval. The information from other strains than MA342 was taken into account with care, because the studies available in the dossier did not confirm the identity of the strain MA342 as belonging to the species . It has been concluded that there is a potential for translocation of MA342 to edible plant parts following seed treatment till an estimated concentration up to about 10 cfu/g and some exposure can be assumed by consumption of fresh commodities. Also, production of the metabolite DDR in the plant cannot be excluded. Regarding levels of DDR in the raw agricultural commodities, exposure estimates based on the limit of quantification (LOQ) for DDR in cereals cannot be further refined while there is no information on the levels of DDR in peas in the dossier. As regards genotoxicity, DDR induced chromosomal damage; however, it was not possible to conclude whether it is through an aneugenic or clastogenic mechanism. Hence, it is not possible to draw a reliable conclusion that DDR is producing an aneugenic effect nor to determine a threshold dose for aneugenicity. Thus, it is not possible to revise the human risk assessment as regards exposure to DDR. The concerns identified in the EFSA conclusion of 2017 remain.
PubMed: 33133274
DOI: 10.2903/j.efsa.2020.6276 -
Microbiology Spectrum Mar 2023Within bacterial communities, community members engage in interactions employing diverse offensive and defensive tools to reach coexistence. Extracellular-matrix...
Within bacterial communities, community members engage in interactions employing diverse offensive and defensive tools to reach coexistence. Extracellular-matrix production and sporulation are defensive mechanisms used by Bacillus subtilis cells when they interact with Pseudomonas chlororaphis strains expressing a type VI secretion system (T6SS). Here, we define Tse1 as the main toxin mobilized by the Pseudomonas chlororaphis T6SS that triggers sporulation in Bacillus subtilis. We characterize Tse1 as a peptidoglycan hydrolase that indirectly alters the dynamics and functionality of the cell membrane. We also delineate the response of cells to Tse1, which through the coordinated actions of the extracellular sigma factor σ and the cytoplasmic histidine kinases KinA and KinB, culminates in activation of the sporulation cascade. We propose that this cellular developmental response permits bacilli to defend against the toxicity of T6SS-mobilized Tse1 effector. The study of bacterial interactions is helping to define species-specific strategies used to modulate the competition dynamics underlying the development of community compositions. In this study, we deciphered the role of Pseudomonas T6SS when competing with and the mechanism by which a T6SS-toxin modifies physiology. We found that Pseudomonas triggers sporulation by injecting through T6SS a toxin that we called Tse1. We found that Tse1 is a hydrolase that degrades peptidoglycan and indirectly damages membrane functionality. In addition, we demonstrated the mechanism by which cells increase the sporulation rate upon recognition of the presence of Tse1. Interestingly, asporogenic cells are more sensitive to T6SS activity, which led us to propose sporulation as a last resort of bacilli to overcome this family of toxins.
PubMed: 36916921
DOI: 10.1128/spectrum.05045-22 -
Molecular Plant-microbe Interactions :... Jul 2021subsp. SPS-41 is a plant growth-promoting rhizobacterium with biocontrol potential that was isolated from the rhizosphere of sweet potato in Xuzhou, Jiangsu Province,...
subsp. SPS-41 is a plant growth-promoting rhizobacterium with biocontrol potential that was isolated from the rhizosphere of sweet potato in Xuzhou, Jiangsu Province, China. Our previous study demonstrated that volatile organic compounds (VOCs) produced by SPS-41 inhibited black spot disease fungi in postharvest sweet potatoes and a variety of other plant pathogens, and the VOCs also displayed strong nematocidal activity. In order to further explore the application potential of this strain, we here report the complete genome sequence of strain SPS-41. The genome consists of one chromosome (6,757,898 bp) with a G+C content 63.10%, which contains 5,951 coding genes, 67 transfer RNA genes, 16 ribosome RNA genes, and 85 other non-coding RNA genes. No plasmid was detected. The information of the genome will provide resources for studying the biocontrol mechanism of this strain.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
Topics: Fungi; Plant Development; Pseudomonas; Rhizosphere
PubMed: 33616420
DOI: 10.1094/MPMI-01-21-0005-A -
Applied and Environmental Microbiology Mar 2023IPD072Aa from Pseudomonas chlororaphis is a new insecticidal protein that has been shown to have high activity against western corn rootworm (WCR). IPD072 has no...
IPD072Aa from Pseudomonas chlororaphis is a new insecticidal protein that has been shown to have high activity against western corn rootworm (WCR). IPD072 has no sequence signatures or predicted structural motifs with any known protein revealing little insight into its mode of action using bioinformatic tools. As many bacterially derived insecticidal proteins are known to act through mechanisms that lead to death of midgut cells, we evaluated whether IPD072Aa also acts by targeting the cells of WCR midgut. IPD072Aa exhibits specific binding to brush border membrane vesicles (BBMVs) prepared from WCR guts. The binding was found to occur at binding sites that are different than those recognized by Cry3A or Cry34Ab1/Cry35Ab1, proteins expressed by current maize traits that target WCR. Using fluorescence confocal microscopy, immuno-detection of IPD072Aa in longitudinal sections from whole WCR larvae that were fed IPD072Aa revealed the association of the protein with the cells that line the gut. High-resolution scanning electron microscopy of similar whole larval sections revealed the disruption of the gut lining resulting from cell death caused by IPD072Aa exposure. These data show that the insecticidal activity of IPD072Aa results from specific targeting and killing of rootworm midgut cells. Transgenic traits targeting WCR based on insecticidal proteins from Bacillus thuringiensis have proven effective in protecting maize yield in North America. High adoption has led to WCR populations that are resistant to the trait proteins. Four proteins have been developed into commercial traits, but they represent only two modes of action due to cross-resistance among three. New proteins suited for trait development are needed. IPD072Aa, identified from the bacterium Pseudomonas chlororaphis, was shown to be effective in protecting transgenic maize against WCR. To be useful, IPD072Aa must work through binding to different receptors than those utilized by current traits to reduce risk of cross-resistance and understanding its mechanism of toxicity could aid in countering resistance development. Our results show that IPD072Aa binds to receptors in WCR gut that are different than those utilized by current commercial traits and its targeted killing of midgut cells results in larval death.
Topics: Animals; Zea mays; Pseudomonas chlororaphis; Endotoxins; Coleoptera; Larva; Bacillus thuringiensis; Insecticides; Bacterial Proteins; Epithelial Cells; Plants, Genetically Modified; Pest Control, Biological
PubMed: 36847510
DOI: 10.1128/aem.01622-22 -
The Journal of General and Applied... Apr 2021Pseudomonas chlororaphis B23 yields nitrile hydratase (NHase) used for the production of 5-cyanovaleramide at the industrial level. Although the nhpC gene (known as...
Pseudomonas chlororaphis B23 yields nitrile hydratase (NHase) used for the production of 5-cyanovaleramide at the industrial level. Although the nhpC gene (known as P47K) located just downstream of the NHase structural genes (nhpAB) has been important for efficient NHase expression, the key role of nhpC remains poorly studied. Here, we purified two NHases expressed in the presence and absence of nhpC, respectively, and characterized them. The purified NHase expressed with nhpC proved to be an iron-containing holo-NHase, while the purified one expressed without nhpC was identified as an apo-NHase, which was iron-deficient. These findings indicated that nhpC would play a crucial role in the post-translational incorporation of iron into the NHase active site as a metal chaperone. In the overall amino acid sequence of NhpC, only the N-terminus exhibited similarities to the CobW protein involved in cobalamin biosynthesis, the UreG and HypB proteins essential for the metallocenter biosynthesis of urease and hydrogenase, respectively. NhpC contains a P-loop motif known as a nucleotide-binding site, and Lys23 and Thr24 are conserved in the P-loop motif in NhpC. Expression analysis of NHase formed in the presence of each mutant NhpC (i.e., K23A and T24A) resulted in immunodetectable production of a mutant NhpC and remarkable expression of NHase lacking the enzyme activity. These findings suggested that an intact P-loop containing Lys23 and Thr24 would be essential for the NhpC function in vivo for the post-translational metallocenter assembly of NHase.
Topics: Amino Acid Sequence; Bacterial Proteins; Binding Sites; Gene Expression Regulation, Bacterial; Gene Expression Regulation, Enzymologic; Hydro-Lyases; Iron; Mutagenesis, Site-Directed; Pseudomonas chlororaphis; Recombinant Proteins; Urease
PubMed: 33162426
DOI: 10.2323/jgam.2020.03.003