Weaponizing volatiles to inhibit competitor biofilms from a distance.

The soil bacterium Bacillus subtilis forms beneficial biofilms that induce plant defences and prevent the growth of pathogens. It is naturally found in the rhizosphere, where microorganisms coexist in an extremely competitive environment, and thus have evolved a diverse arsenal of defence mechanisms. In this work, we found that volatile compounds produced by B. subtilis biofilms inhibited the development of competing biofilm colonies, by reducing extracellular matrix gene expression, both within and across species. This effect was dose-dependent, with the structural defects becoming more pronounced as the number of volatile-producing colonies increased. This inhibition was mostly mediated by organic volatiles, and we identified the active molecules as 3-methyl-1-butanol and 1-butanol. Similar results were obtained with biofilms formed by phylogenetically distinct bacterium sharing the same niche, Escherichia coli, which produced the biofilm-inhibiting 3-methyl-1-butanol and 2-nonanon. The ability of established biofilms to inhibit the development and spreading of new biofilms from afar might be a general mechanism utilized by bacterial biofilms to protect an occupied niche from the invasion of competing bacteria.

Harvesting the complex pathways of antibiotic production and resistance of soil bacilli for optimizing plant microbiome.

A sustainable future increasing depends on our capacity to utilize beneficial plant microbiomes to meet our growing needs. Plant microbiome symbiosis is a hallmark of the beneficial interactions between bacteria and their host. Specifically, colonization of plant roots by biocontrol agents and plant growth-promoting bacteria can play an important role in maintaining the optimal rhizosphere environment, supporting plant growth and promoting its fitness. Rhizosphere communities confer immunity against a wide range of foliar diseases by secreting antibiotics and activating plant defences. At the same time, the rhizosphere is a highly competitive niche, with multiple microbial species competing for space and resources, engaged in an arms race involving the production of a vast array of antibiotics and utilization of a variety of antibiotic resistance mechanisms. Therefore, elucidating the mechanisms that govern antibiotic production and resistance in the rhizosphere is of great significance for designing beneficial communities with enhanced biocontrol properties. In this review, we used Bacillus subtilis and B. amyloliquefaciens as models to investigate the genetics of antibiosis and the potential for its translation of into improved plant microbiome performance.

The extracellular matrix protein TasA is a developmental cue that maintains a motile subpopulation within Bacillus subtilis biofilms.

In nature, bacteria form biofilms-differentiated multicellular communities attached to surfaces. Within these generally sessile biofilms, a subset of cells continues to express motility genes. We found that this subpopulation enabled Bacillus subtilis biofilms to expand on high-friction surfaces. The extracellular matrix (ECM) protein TasA was required for the expression of flagellar genes. In addition to its structural role as an adhesive fiber for cell attachment, TasA acted as a developmental signal stimulating a subset of biofilm cells to revert to a motile phenotype. Transcriptomic analysis revealed that TasA stimulated the expression of a specific subset of genes whose products promote motility and repress ECM production. Spontaneous suppressor mutations that restored motility in the absence of TasA revealed that activation of the biofilm-motility switch by the two-component system CssR/CssS antagonized the TasA-mediated reversion to motility in biofilm cells. Our results suggest that although mostly sessile, biofilms retain a degree of motility by actively maintaining a motile subpopulation.

Complete Genome Sequence of Bacillus velezensis DSYZ, a Plant Growth-Promoting Rhizobacterium with Antifungal Properties.

Bacillus velezensis DSYZ is a plant growth-promoting rhizobacterium with the capacity to control fungal pathogens. It was isolated from the rhizosphere soil of garlic. Here, we present the complete genome sequence of B. velezensis DSYZ. Several gene clusters that are related to the biosynthesis of antimicrobial compounds were predicted.

Screening and Whole-Genome Sequencing of Two Streptomyces Species from the Rhizosphere Soil of Peony Reveal Their Characteristics as Plant Growth-Promoting Rhizobacteria.

Two bacteria, Streptomyces albireticuli MDJK11 and S. alboflavus MDJK44, which are potential plant growth-promoting rhizobacteria against pathogenic fungi were isolated from the rhizosphere soil of peony in Shandong, China. Their biological characteristics and complete genome sequences were reported in this study. The total genome size of MDJK11 was only 8.14 Mb with 6,550 protein-coding genes and a high GC content of 72.8 mol%. The MDJK44 genome comprises a 9.62 Mb chromosome with 72.1 mol% GC content, 7,285 protein-coding genes, and two plasmids. Some gene sequences in these two genomes were analyzed to be heterologously obtained by horizontal transfer. Gene or gene cluster candidates responding to secondary metabolites production, antimicrobial activities, and plant growth-promoting capacities were also analyzed in this paper. The genomic information and biological characteristics will facilitate the understanding and application of S. albireticuli and S. alboflavus species as biocontrol agents in future agriculture.

Complete Genome Sequence of Bacillus velezensis GQJK49, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus velezensis GQJK49 is a plant growth-promoting rhizobacterium with antifungal activity, which was isolated from Lycium barbarum L. rhizosphere. Here, we report the complete genome sequence of B. velezensis GQJK49. Twelve gene clusters related to its biosynthesis of secondary metabolites, including antifungal and antibacterial antibiotics, were predicted.

Complete Genome Sequence of Biocontroller Bacillus velezensis Strain JTYP2, Isolated from Leaves of Echeveria laui.

Bacillus velezensis JTYP2 was isolated from the leaves of Echeveria laui in Qingzhou, China, and may control some of the fungal pathogens of the plant. Here, we present the complete genome sequence of B. velezensis JTYP2. Several gene clusters related to its biosynthesis of antimicrobial compounds were predicted.

Complete Genome Sequence of Bacillus subtilis GQJK2, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus subtilis GQJK2 is a plant growth-promoting rhizobacterium with antifungal activity which was isolated from Lycium barbarum L. rhizosphere. Here, we report the complete genome sequence of B. subtilis GQJK2. Ten gene clusters involved in the biosynthesis of antagonistic compounds were predicted.

Complete Genome Sequence of Bacillus paralicheniformis MDJK30, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus paralicheniformis MDJK30 was isolated from the rhizosphere of a peony. It could control the pathogen of peony root rot. Here, we report the complete genome sequence of B. paralicheniformis MDJK30. Eleven secondary metabolism gene clusters were predicted.

Complete Genome Sequence of Paenibacillus polymyxa YC0136, a Plant Growth-Promoting Rhizobacterium Isolated from Tobacco Rhizosphere.

Paenibacillus polymyxa strain YC0136 is a plant growth-promoting rhizobacterium with antimicrobial activity, which was isolated from tobacco rhizosphere. Here, we report the complete genome sequence of P. polymyxa YC0136. Several genes with antifungal and antibacterial activity were discovered.

Complete Genome Sequence of Paenibacillus polymyxa YC0573, a Plant Growth-Promoting Rhizobacterium with Antimicrobial Activity.

Paenibacillus polymyxa strain YC0573 is a plant growth-promoting rhizobacterium with antimicrobial activity, which was isolated from tobacco rhizosphere. Here, we report the complete genome sequence of P. polymyxa YC0573. Antifungal and antibacterial genes were discovered.

Draft Genome Sequence of Bacillus methylotrophicus FKM10, a Plant Growth-Promoting Rhizobacterium Isolated from Apple Rhizosphere.

Bacillus methylotrophicus FKM10 is a strain of plant growth-promoting rhizobacterium with antimicrobial activity, which was isolated from apple rhizosphere. Here, we present the genome sequence of B. methylotrophicus FKM10. Two scaffolds were finally assembled, and several functional genes related to its antimicrobial activity were discovered.

Draft Genome Sequence of Delftia tsuruhatensis MTQ3, a Strain of Plant Growth-Promoting Rhizobacterium with Antimicrobial Activity.

Delftia tsuruhatensis MTQ3 is a plant growth-promoting rhizobacterium (PGPR) isolated from tobacco rhizosphere. Here, we report the draft genome sequence of D. tsuruhatensis MTQ3. Several functional genes related to antimicrobial activity and environment adaption have been found in the genome. This is the first genome sequence of D. tsuruhatensis related to PGPR.

Draft Genome Sequence of Brevibacillus brevis DZQ7, a Plant Growth-Promoting Rhizobacterium with Broad-Spectrum Antimicrobial Activity.

Brevibacillus brevis DZQ7 is a plant growth-promoting rhizobacterium (PGPR) isolated from tobacco rhizosphere. Here, we report the draft genome sequence of B. brevis DZQ7. Several functional genes related to antimicrobial activity were identified in the genome.

Detection of bioavailable cadmium, lead, and arsenic in polluted soil by tailored multiple Escherichia coli whole-cell sensor set.

Microbial whole-cell sensor has been widely used to assess bioavailability and risk of toxic elements, but their environmental use is still limited due to the presence of other interfering pollutants and the nonspecific binding in cells, which leads to inaccurate results. Here, we proposed a strategy combining Escherichia coli sensor set with binary regression models for the specific detection of bioavailable cadmium (Cd), lead (Pb), and arsenic (As) in a co-polluted environment. Initial tests suggested that the sensor set respectively termed pcadCluc, pzntRluc, and parsRluc could be classified into two groups according to their specific response to Cd, Pb, and As: group 1 (pcadCluc and pzntRluc) induced by a Cd-Pb mix and group 2 (parsRluc) induced by a Cd-As mix. Based on the variance in responses of each sensor to mixtures of target elements, three binary linear equations for two sensor groups were set up to calculate the individual concentrations in the mixture solutions. This method was then used to quantify the bioavailable Cd, Pb, and As in soils from a co-polluted mining region and to compare the results with other methods. Results showed that the conventional single target sensor method overestimated the bioavailability of each element, while sensor set was credible for accurate bioavailable Cd, Pb, and As quantification and comparable with the results from inductively coupled plasma mass spectrometry (ICP-MS) analysis. Our method can potentially be extended to cover the specific detection of other bioavailable toxic elements in different environmental settings.

The impacts of different long-term fertilization regimes on the bioavailability of arsenic in soil: integrating chemical approach with Escherichia coli arsRp::luc-based biosensor.

An Escherichia coli arsRp::luc-based biosensor was constructed to measure the bioavailability of arsenic (As) in soil. In previous induction experiments, it produced a linear response (R (2) = 0.96, P < 0.01) to As from 0.05 to 5 µmol/L after a 2-h incubation. Then, both chemical sequential extraction, Community Bureau of Reference recommended sequential extraction procedures (BCR-SEPs) and E. coli biosensor, were employed to assess the impact of different long-term fertilization regimes containing N, NP, NPK, M (manure), and NPK + M treatments on the bioavailability of arsenic (As) in soil. Per the BCR-SEPs analysis, the application of M and M + NPK led to a significant (P < 0.01) increase of exchangeable As (2-7 times and 2-5 times, respectively) and reducible As (1.5-2.5 times and 1.5-2.3 times, respectively) compared with the no fertilization treated soil (CK). In addition, direct contact assay of E. coli biosensor with soil particles also supported that bioavailable As in manure-fertilized (M and M + NPK) soil was significantly higher (P < 0.01) than that in CK soil (7 and 9 times, respectively). Organic carbon may be the major factor governing the increase of bioavailable As. More significantly, E. coli biosensor-determined As was only 18.46-85.17 % of exchangeable As and 20.68-90.1 % of reducible As based on BCR-SEPs. In conclusion, NKP fertilization was recommended as a more suitable regime in As-polluted soil especially with high As concentration, and this E. coli arsRp::luc-based biosensor was a more realistic approach in assessing the bioavailability of As in soil since it would not overrate the risk of As to the environment.

Assessing the effect of phosphate and silicate on Cd bioavailability in soil using an Escherichia coli cadAp::luc-based whole-cell sensor.

An Escherichia coli cadAp::luc-based whole-cell sensor was constructed to measure cadmium (Cd) bioavailability and assess the immobilizing efficiency of phosphate and silicate on Cd. In previous induction experiments, a linear response (R(2) = 0.97, P < 0.01) from 0.1 to 5 µmol L(-1) of Cd was detected by this sensor after a 2 h incubation. The sensor was then used to estimate Cd bioavailability in soils spiked with different amounts of dipotassium phosphate (DKP, K2HPO4) or sodium silicate (SS, Na2SiO3·9H2O). The total Cd in soil-water extracts (TSWE) was determined with ICP-MS, and the bioavailable Cd in soil-water extracts (BSWE) and bioavailable Cd in soil-water suspensions (BSWS) were measured by the E. coli cadAp::luc-based whole-cell sensor. Final results showed that spiked SS (Si : Cd = 2 : 1, mol mol(-1)) reduced the different forms of Cd (TSWE, BSWE and BSWS) from 56.47 mg kg(-1), 42.11 mg kg(-1), and 206.72 mg kg(-1) to 16.63 mg kg(-1), 15.90 mg kg(-1), and 67.57 mg kg(-1), respectively. In other words, SS had 25.68%, 19.5%, and 9.54% better immobilizing efficiency, respectively, compared with DKP. All the results supported SS was more efficient than DKP at immobilizing Cd in soil, and higher soil pH and higher solubility of the immobilizing agents may have been the major factor affecting immobilizing efficiency. In addition, the total and bioavailable Cd in soil-water extracts was only 16.13-35.41% of the sensor contact assay-determined Cd (BSWS), which indicated that the whole-cell sensor-based contact assay was more practical in assessing the risk of Cd in soil after immobilization since it would not overrate the immobilizing capacity of the agents.

[Construction and properties of a microbial whole-cell sensor CB10 for the bioavailability detection of Cr6+].

A microbial whole-cell biosensor CB10 for the bioavailability assessing of Cr6+ was constructed by molecular biotechnology. The regulatory gene and promoter of CB10 was from the chromium resistance system of plasmid pMOL28 from Cupriavidus metallidurans CH34, and the reporter gene of CB10 was luc which was derived from Photinus pyralis. Finally, its response characteristic was discussed under different incubation conditions e. g. pH and temperature. The results showed that a microbial whole-cell biosensor CB10 had been successfully constructed which could respond to Cr6+ within 30 min, with a LOD for Cr6+ of 2 micromol x L(-1). When the incubation concentration of Cr6+ was between 20 micromol x L(-1) and 200 micromol x L(-1), the luc activity of the CB10 biosensor was in linear correlation with the concentration of Cr6+. When the concentration of heavy metal was in the range of 10-50 micromol x L(-1), the response of CB10 was relatively more specific. Moreover, high concentrations of Pb2+, Mn2+ and Sb2+ could also induce CB10. By analyzing the response characteristic of CB10 biosensor, we could draw the conclusion that 15-30 degrees C and pH 4-7 were appropriate for CB10, and 30 degrees C and pH 7 were the optimal conditions for the incubation of the CB10 biosensor. The microbial whole-cell biosensor CB10 for the detection of Cr6+ was fast-responding, specific, sensitive and stable under various conditions. In prospective, it could be used in the fast detection of Cr6+ in water and assessment of the bioavailability of Cr6+ in soil.

[Advance in the bioavailability monitoring of heavy metal based on microbial whole-cell sensor].

Microbial whole-cell biosensor is an excellent tool to assess the bioavailability of heavy metal in soil and water. However, the traditional physicochemical instruments are applied to detect the total metal. Furthermore, microbial whole-cell biosensor is simple, rapid and economical in manipulating, and is thus a highly qualified candidate for emergency detection of pollution incidents. The biological component of microbial whole-cell biosensor mostly consists of metalloregulatory proteins and reporter genes. In detail, metalloregulatory proteins mainly include the MerR family, ArsR family and RS family, and reporter genes mainly include gfp, lux and luc. Metalloregulatory protein and reporter gene are related to the sensitivity, specificity and properties in monitoring. The bioavailability of heavy metals is alterable under different conditions, influenced by pH, chelate and detection methods and so on. Increasing the accumulation of intracellular heavy metal, modifying the metalloregulatory proteins and optimizing the detecting conditions are important for improving the sensitivity, specificity and accuracy of the microbial whole-cell biosensor. The future direction of microbial whole-cell biosensor is to realize the monitoring of pollutions in situ and on line.