A heterotrophic arsenite [As(III)]-oxidizing bacterium Agrobacterium tumefaciens GW4 isolated from As(III)-rich groundwater sediment showed high As(III) resistance and could oxidize As(III) to As(V). The As(III) oxidation could generate energy and enhance growth, and AioR was the regulator for As(III) oxidase. To determine the related metabolic pathways mediated by As(III) oxidation and whether AioR regulated other cellular responses to As(III), isobaric tags for relative and absolute quantitation (iTRAQ) was performed in four treatments, GW4 (+AsIII)/GW4 (-AsIII), GW4-ΔaioR (+AsIII)/GW4-ΔaioR (-AsIII), GW4-ΔaioR (-AsIII)/GW4 (-AsIII) and GW4-ΔaioR (+AsIII)/GW4 (+AsIII). A total of 41, 71, 82 and 168 differentially expressed proteins were identified, respectively. Using electrophoretic mobility shift assay (EMSA) and qRT-PCR, 12 genes/operons were found to interact with AioR. These results indicate that As(III) oxidation alters several cellular processes related to arsenite, such as As resistance (ars operon), phosphate (Pi) metabolism (pst/pho system), TCA cycle, cell wall/membrane, amino acid metabolism and motility/chemotaxis. In the wild type with As(III), TCA cycle flow is perturbed, and As(III) oxidation and fermentation are the main energy resources. However, when strain GW4-ΔaioR lost the ability of As(III) oxidation, the TCA cycle is the main way to generate energy. A regulatory cellular network controlled by AioR is constructed and shows that AioR is the main regulator for As(III) oxidation, besides, several other functions related to As(III) are regulated by AioR in parallel.

Pesticide usage is becoming increasingly necessary to escalate agricultural productivity and meet food production needs. However, it harms in different degrees all living organisms, plants, and animals, whether terrestrial or aquatic. Soil microorganisms, are microbes belonging to microorganisms, are the first to be specifically affected by pesticides. This study aims to evaluate the impact of two herbicides, paraquat and glyphosate, on symbiotic nitrogen-fixing bacteria. Our study was carried out in the greenhouse. Bituminaria bituminosa plants were inoculated with four different nitrogen-fixing bacteria, Pantoea agglomerans, Rhizobium nepotum, Rhizobium radiobacter, and Rhizobium tibeticum, and then treated with varying herbicide concentrations were selected according to the doses recommended by the National Office of Food Safety (ONSSA) and according to a survey conducted among farmers in the Meknes region-Morocco, (0.05, 0.1, 5.4, 10.8 g/L glyphosate and 0.05, 0.1, 2, 4 g/L paraquat). After 6 months after sowing, the following parameters were evaluated: nodule number, nodule mass, nodule weight, nodule dry, and fresh weight, nitrogen content, and symbiotic efficiency. At higher doses (5.4, 10.8 g/L for glyphosate and 2, 4 g/L for paraquat), both herbicides decreased the number and the size of nodules, the weight of nodules, nitrogen content of Bituminaria bituminosa and symbiotic efficiency of the four different nitrogen-fixing bacteria studied. The effect of herbicides increased as the used concentration increased. The current research demonstrates that the decreased growth of herbicide-treated plants was caused by herbicides' direct effects on rhizobia rather than herbicides' indirect effects on Bituminaria bituminosa.

The fixed-film sequencing batch reactor, or F-SBR, was developed to treat high organic compound levels and toxic cyanide concentrations in cassava wastewater. The performance of the F-SBR was compared with that of a conventional sequencing batch reactor, or SBR, that was operated with organic compound contents of 16,266.67–26,666 mg COD/L and 132.92–252.66 mg CN⁻/L. The cyanide and chemical oxygen demand removal efficiencies of the conventional SBR system were 42.61% and 36.83%, respectively, while those of the F-SBR were 77.95% and 74.43%, respectively; the cyanide removal efficiency reached 95.45% when the hydraulic retention time was increased to 5 days, and the F-SBR was very effective for the complete removal of cyanide when the hydraulic retention time was increased to 10 days. This effectiveness was similar to the effectiveness of chemical oxygen demand removal, which reached 40–78% efficiency with the F-SBR system. These results showed that the immobilization of cyanide-degrading bacteria such as Agrobacterium tumefaciens SUTS 1 and Pseudomonas monteilii SUTS 2 carried out with a polypropylene ring in a fixed-film aerobic system enhanced the performance of the reactor and can be successfully applied for cyanide and chemical oxygen demand removal from industrial wastewater with high cyanide and chemical oxygen demand concentrations. This study may provide a promising alternative technique that reduces economic operation costs in solving wastewater contamination problems.

Chlorpyrifos (CP) is a widely used organophosphate (OP) insecticide and a potent environmental neurotoxin. This research focuses on the potential of bacteria, both native to agricultural soil and part of a designed consortium composed of laboratory strains, to completely degrade CP and its toxic metabolites. Metabolite production and degradation kinetics analysis through gas chromatography-mass spectrophotometry (GCMS) analysis was conducted on native soil samples and compared to soil spiked with different combinations of bacterial consortia over 7 days to determine the effectiveness of CP degradation in both non-augmented and augmented soil. GCMS analysis of augmented soil samples inoculated with putative microbial CP degradation activity identified four CP metabolites, including 3,5,6-trichloropyridinol (TCP), phosphorothioic acid, fumaric acid, and ethanol. Non-augmented ranch and crop field soil also displayed a greater native degradation capacity than garden soil, possibly due to greater pesticide exposure. CP-inoculated soil spiked with a 3-strain consortium exhibited the highest degradation rate, with 78.55% of CP degraded within 48 h. Overall, degradation kinetics for augmented and non-augmented soil samples showed that CP had an average half-life of 1.03 and 5.45 days, respectively. The outcome of this study suggests that while native agricultural populations are capable of CP degradation, supplementing contaminated soil with a bacterial consortium consisting of Pseudomonas putida CBF10-2, Ochrobactrum anthropi FRAF13, and Rhizobium radiobacter GHKF11 could be a highly efficient and safe biological approach to facilitating rapid and efficient CP degradation in agriculture.

Chemical cross-linking and the high molecular weight of superabsorbent copolymers (SAPs) are the two main causes of their resistance to biodegradation. However, SAP particles are colonized by microorganisms. For the purposes of this study, the dry technical copolymer of acrylamide and potassium acrylate containing 5.28 % of unpolymerized monomers was wrapped in a geotextile and incubated in unsterile Haplic Luvisol soil as a water absorbing geocomposite. The highest number of soil bacteria that colonized the hydrated SAP and utilized it as the sole carbon and energy source was found after the first month of incubation in soil. It was equal to 7.21–7.49 log₁₀ cfu g⁻¹ of water absorbed by the SAP and decreased by 1.35–1.61 log₁₀ units within the next 8 months. During this time, the initial SAP water holding capacity of 1665.8 g has decreased by 24.40 %. Moreover, the 5 g of SAP dry mass has declined by 31.70 %. Two bacteria, Rhizobium radiobacter 28SG and Bacillus aryabhattai 31SG isolated from the watered SAP were found to be able to biodegrade this SAP in pure cultures. They destroyed 25.07 and 41.85 mg of 300 mg of the technical SAP during the 60-day growth in mineral Burk’s salt medium, and biodegradation activity was equal to 2.95 and 6.72 μg of SAP μg⁻¹ of protein, respectively. B. aryabhattai 31SG and R. radiobacter 28SG were also able to degrade 9.99 and 29.70 mg of 82 mg of the ultra-pure SAP in synthetic root exudate medium during the 30-day growth, respectively.

Six organophosphate-degrading bacterial strains collected from farm and ranch soil rhizospheres across the Houston-metropolitan area were identified as strains of Pseudomonas putida (CBF10-2), Pseudomonas stutzeri (ODKF13), Ochrobactrum anthropi (FRAF13), Stenotrophomonas maltophilia (CBF10-1), Achromobacter xylosoxidans (ADAF13), and Rhizobium radiobacter (GHKF11). Whole genome sequencing data was assessed for relevant genes, proteins, and pathways involved in the breakdown of agrochemicals. For comparative purposes, this analysis was expanded to also include data from deposited strains in the National Center for Biotechnology Information’s (NCBI) database. This study revealed Zn-dependent metallo-β-lactamase (MBL)-fold proteins similar to OPHC2 first identified in P. pseudoalcaligenes as the likely agents of organophosphate (OP) hydrolysis in A. xylosoxidans ADAF13, S. maltophilia CBF10-1, O. anthropi FRAF13, and R. radiobacter GHKF11. A search of similar proteins within NCBI identified over 200 hits for bacterial genera and species with a similar OPHC2 domain. Taken together, we conclude from this data that intrinsic low-level OP hydrolytic activity is likely prevalent across the rhizosphere stemming from widespread OPHC2-like metalloenzymes. In addition, P. stutzeri ODKF13, P. putida CBF10-2, O. anthropi FRAF13, and R. radiobacter GHKF11 were found to harbor glycine oxidase (GO) enzymes that putatively possess low-level activity against the herbicide glyphosate. These bacterial GOs are reported to catalyze the degradation of glyphosate to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and suggest a possible link to AMPA that can be found in glyphosate-contaminated agricultural soil. The presence of aromatic degradation proteins were also detected in five of six study strains, but are attributed primarily to components of the widely distributed β-ketoadipate pathway found in many soil bacteria.

In this research, the optimum growth conditions for two zinc solubilizing bacteria (ZSB) have been studied for their potential application as bioinoculants to overcome Zn unavailability in soils. For this purpose, a laboratory-scale experiment was carried out to evaluate the zinc solubilizing ability of 80 plant growth promoting bacteria (PGPB) strains isolated from the rhizosphere of barley and tomato plants. To select effective ZSB, isolates were evaluated on Tris-mineral medium supplemented separately with zinc oxide, zinc carbonate, and zinc phosphate at a concentration of 0.1%. Two strains (Agrobacterium tumefaciens and Rhizobium sp.) were selected, based on a clear halo zone around their colonies in the solid medium supplemented with zinc oxide after 10 days of incubation at 29 °C. Results of solubilization at different pH values showed that these strains had solubilization activity in the range of pH 8–10 while no solubilization was observed at pH 6 and 7. The maximum Zn solubilization values were noted at pH 9: 51.4 mg L⁻¹ (Agrobacterium tumefaciens) and 72.1 mg L⁻¹ (Rhizobium sp). According to findings, bacterial growth was affected by different NaCl concentrations under in vitro condition. The salt concentration required for 50% inhibition of absorbance was 2.11 and 2.27% NaCl for Agrobacterium tumefaciens and Rhizobium sp., respectively. The maximum bacterial growth was observed at about 0.8% NaCl concentration.

Despite the potential biological importance of lipopeptides from Bacillus amyloliquefaciens as antimicrobial compounds, their effects on Agrobacterium tumefaciens biofilms have not been previously studied. These latter are important virulence factors for the development and re-occurrence of crown gall disease. As part of the development of a new biopesticide acting as anti-biofilm and biocontrol agent, we investigated for the first time the ability of a mixture of lipopeptides produced by B. amyloliquefaciens strain 32a to inhibit the tumor formation on plants and to reduce the formation of biofilms by the phytopathogenic A. tumefaciens strains C58 and B6. The mixture was found to display a strong biosurfactant activity as well as bactericidal activity against planktonic Agrobacterium cells. Moreover, the lipopeptide treatment inhibited biofilm formation in the range of 79.58 ± 0.60–100.00 ± 0.00% and dislodged 43.42 ± 0.91–93.89 ± 2.70% of preformed biofilm. For these assays, fluorescence microscopy did not show any adherent cell in the anti-adhesive assay and only few ones in the cell-dislodging assay. More importantly, lipopeptide-enriched extract inhibits tumor formation on tomato stem when treatments were applied after pathogen adhesion to wounded tissues. By virtue of its ability to inhibit biofilms formed on biotic and abiotic surfaces and to control efficiently tumor development, the 32a lipopeptide mixture may represent an excellent new tool for an efficient biocontrol of crown gall disease.

Phytoremediation comprises a set of plant and microbe-based technologies for remediation of soil heavy metal contamination. In this work, four Pb-resistant bacteria (Agrobacterium tumefaciens, Rahnella aquatilis, and two Pseudomonas sp.) were selected among a collection of isolates from root nodule of Lens culinaris. They had a high degree of bioaccumulation ability in nutrient medium containing 2 mM Pb, and the maximum Pb accumulation of whole cell was found after 48-h incubation. These Pb-resistant bacteria synthesized plant growth promoting substances such as indole acetic acid and siderophore. The presence of the Pb resistance genes (pbrA) in these bacteria has been confirmed by PCR. L. culinaris cultivated in two experimental soils with different levels of contamination showed that Pb contamination affected plant growth; therefore, it’s co-inoculation with the consortium of Pb-resistant bacteria improved plant biomass. The present study demonstrated that lentil accumulated Pb primarily in their roots and poorly in their shoots; in addition, it’s co-inoculation in moderately Pb-contaminated soil induced a reduction in Pb accumulation in roots and shoots by 22 and 80 %, respectively. Whereas in highly Pb-contaminated soil, we registered a diminution in concentration of Pb in shoots (66 %) and an augmentation in roots (21 %). The contamination of soil by Pb caused an oxidative stress in lentil plant, inducing modulation in antioxidant enzymes activities, essentially in superoxide dismutase (SOD) and peroxidase (GPOX) activities which were more pronounced in lentil cultivated in highly Pb-contaminated soil, in addition, co-inoculation enhanced these activities, suggesting the protective role of enzymatic antioxidant against Pb-induced plant stress.Thus, the present study demonstrated that co-inoculation of lentil with A. tumefaciens, R. aquatilis, and Pseudomonas sp. formed a symbiotic system useful for phytostabilization of highly and moderately Pb-contaminated soils.