Several studies have explored the utilization of soil microorganisms, to address the environmental issues associated with glyphosate use and enhance crop yields. In our investigation, screening on Agar plate and broth medium  Luria Bertani was carried out after isolating bacterial strains from rhizospheric agricultural soil in Mascara,  Algeria, to biodegrade glyphosate, following that by testing the Plant Growth-Promoting Rhizobacteria and evaluate the effects of glyphosate on these proprieties. Our findings indicate that five bacterial strains exhibited growth in the presence of glyphosate concentrations up to 25 mg/ml, beyond this concentration the strains have developed tolerance. Following a partial examination of the 16S rRNA sequences, the bacterial strains were identified as belonging to the genus of Enterobacter. After 10 days of incubation with the glyphosate, Phosphate solubilization decreased in broth and agar Pikovskaya medium and the bacterial strains synthetized less of indole-3-acetic acid compared to the control, indicating the impact of glyphosate on these outcomes, high concentration of glyphosate inhibited nitrogen fixation, and various doses of glyphosate were found to restrict the growth of biofilms in these strains. The results of HPLC examination of secondary metabolites revealed that the primary degradation products of glyphosate in all strains were Sarcosine and Glycine. So, it seemed that the strain could both biodegrade glyphosate and use it for growth ,while also possessing rhizobacteria properties that promote plant development, enabling the use of the strains in the bioremediation of glyphosate-contaminated soils.

In this study, a strain of lactic acid bacteria Streptococcus salivarius was studied for its capacity to remove hexavalent chromium (Cr (VI)) from a liquid medium and to form biofilm. Both properties are useful for using the strain in bioremediation of metal-contaminated effluents. For biofilm formation capacity, three methods were used: the tube method (TM), the Congo red agar method (CRA) and adherence to polystyrene tissue culture plate method (TCP). S. salivarius, showed a positive-biofilm and a correlation between the three methods was noted. The bacterial surface hydrophobicity was studied using the microbial adhesion to solvents method (MATS). On AISI-316 L stainless steel, the strain with a hydrophobic surface showed a good adhesion on this support after 18 h incubation. The colonization of the supports and the biofilms formation by the bacterial cell was observed using scanning electron microscopy (SEM). The minimum inhibitory concentration (MIC) of Cr(VI) on S. salivarius was determined on MRS broth, it was relatively high and equal to 400mg/l. In addition, it displayed a remarkable capacity to reduce Cr(VI) concentration on the liquid medium containing initially 50 mg/l of Cr(VI) ; the percent removal rate was equal to approximately 42% after 72 h of incubation at 37 °C. In addition to its GRAS status, the obtained results suggested that S. salivarius could be successfully used in Cr(VI) bioremediation.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA | This study is a first attempt to investigate the impact of urban contamination on metal tolerance of heterotrophic river biofilms using a short-term test based on β-glucosidase activity. Tolerance levels to Cu, Cd, Zn, Ni and Pb were evaluated for biofilms collected at three sites along an urban gradient in the Seine river (France). Metallic pollution increased along the river, but concentrations remained low compared to environmental quality standards. Biofilm metal tolerance increased downstream from the urban area. Multivariate analysis confirmed the correlation between tolerance and contamination and between multi-metallic and physico-chemical gradients. Therefore, tolerance levels have to be interpreted in relation to the whole chemical and physical characteristics and not solely metal exposure. We conclude that community tolerance is a sensitive biological response to urban pressure and that mixtures of contaminants at levels lower than quality standards might have a significant impact on periphytic communities.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

International audience | Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients.

Microplastic pollution has attracted significant attention as an emerging global environmental problem. One of the most important issues with microplastics is the leaching of harmful additives. This review summarizes the recent advances in the understanding of the leaching phenomena in the context of the phase equilibrium between microplastics and water, and the release kinetics. Organic additives, which are widely used in plastic products, have been introduced because they have diverse physicochemical properties and mass fractions in plastics. Many theoretical and empirical models have been utilized in laboratory and field studies. However, the partition or distribution constant between microplastics and water (Kₚ) and the diffusivity of an additive in microplastics (D) are the two key properties explaining the leaching equilibrium and kinetics of hydrophobic organic additives. Because microplastics in aquatic environments undergo dynamic weathering, leaching of organic additives with high Kₚ and/or low D cannot be described by a leaching model that only considers microplastic and water phases with a fixed boundary. Surface modifications of microplastics as well as biofilms colonizing microplastic surfaces can alter the leaching equilibrium and kinetics and transform additives. Further studies on the release of hydrophobic organic additives and their transformation products under various conditions are required to extend our understanding of the environmental fate and transport of these additives in aquatic environments.

Forest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1–5) within three river basins with different total disturbances from forestry (both harvesting and silviculture). Methylmercury levels were highest in water and some food sources from the basin with moderate disturbance (greater clearcutting but less silviculture). Water, leaves, stoneflies and fish increased in MeHg or total Hg along the river continuum in the least disturbed basin, and there were some dissipative effects of forest management on these spatial patterns. Trophic level (δ¹⁵N) was a significant predictor of MeHg (and total Hg in fish) within food webs across all 18 sites, and biomagnification slopes were significantly lower in the basin with moderate total disturbance but not different in the other two basins. The elevated MeHg in lower trophic levels but its reduced trophic transfer in the basin with moderate disturbance was likely due to greater inputs of sediments and of dissolved organic carbon that is more humic, as these factors are known to both increase transport of Hg to streams and its uptake in primary producers but to also decrease MeHg bioaccumulation in consumers. Overall, these results suggest that the type of disturbance from forestry affects MeHg bioaccumulation and trophic transfer in stream food webs and some longitudinal patterns along a river continuum.

Bensulfuron-methyl (BSM) residues in soil threaten the rotation of BSM-sensitive crops. Microbial biofilms formed on crop roots could improve the ability of microbes to survive and protect crop roots. However, the research on biofilms with the purpose of mitigating or even eliminating BSM damage to sensitive crops is very limited. In this study, one BSM-degrading bacterium, Hansschlegelia zhihuaiae S113, colonized maize roots by forming a biofilm. Root exudates were associated with increased BSM degradation efficiency with strain S113 in rhizosphere soil relative to bulk soil, so the interactions among BSM degradation, root exudates, and biofilms may provide a new approach for the BSM-contaminated soil bioremediation. Root exudates and their constituent organic acids, including fumaric acid, tartaric acid, and l-malic acid, enhanced biofilm formation with 13.0–22.2% increases, owing to the regulation of genes encoding proteins responsible for cell motility/chemotaxis (fla/che cluster) and materials metabolism, thus promoting S113 population increases. Additionally, root exudates were also able to induce exopolysaccharide production to promote mature biofilm formation. Complete BSM degradation and healthy maize growth were found in BSM-contaminated rhizosphere soil treated with wild strain S113, compared to that treated with loss-of-function mutants ΔcheA-S113 (89.3%, without biofilm formation ability) and ΔsulE-S113 (22.1%, without degradation ability) or sterile water (10.7%, control). Furthermore, the biofilm mediated by organic acids, such as l-malic acid, exhibited a more favorable effect on BSM degradation and maize growth. These results showed that root exudates and their components (such as organic acids) can induce the biosynthesis of the biofilm to promote BSM degradation, emphasizing the contribution of root biofilm in reducing BSM damage to maize.

Mutations are an important origin of antibiotic resistance in bacteria. While there is increasing evidence showing promoted resistance mutations by environmental stresses, no retrospective research has yet been conducted on this phenomenon and its mechanisms. Herein, we summarized the phenomena of stress-elevated resistance mutations in bacteria, generalized the regulatory mechanisms and discussed the environmental and human health implications. It is shown that both chemical pollutants, such as antibiotics and other pharmaceuticals, biocides, metals, nanoparticles and disinfection byproducts, and non-chemical stressors, such as ultraviolet radiation, electrical stimulation and starvation, are capable of elevating resistance mutations in bacteria. Notably, resistance mutations are more likely to occur under sublethal or subinhibitory levels of these stresses, suggesting a considerable environmental concern. Further, mechanisms for stress-induced mutations are summarized in several points, namely oxidative stress, SOS response, DNA replication and repair systems, RpoS regulon and biofilm formation, all of which are readily provoked by common environmental stresses. Given bacteria in the environment are confronted with a variety of unfavorable conditions, we propose that the stress-elevated resistance mutations are a universal phenomenon in the environment and represent a nonnegligible risk factor for ecosystems and human health. The present review identifies a need for taking into account the pollutants’ ability to elevate resistance mutations when assessing their environmental and human health risks and highlights the necessity of including resistance mutations as a target to prevent antibiotic resistance evolution.

The composition of root exudates is modulated by several environmental factors, and it remains unclear how that affects beneficial rhizosphere or inoculated microorganisms under heavy metal (HM) contamination. Therefore, we evaluated the transcriptional response of Pseudomonas putida E36 (a Miscanthus x giganteus isolate with plant growth promotion-related properties) to Cd, Pb and Zn in an in vitro study implementing root exudates from M. x giganteus. To collect root exudates and analyse their composition plants were grown in a pot experiment under HM and control conditions. Our results indicated higher exudation rate for plants challenged with HM. Further, out of 29 organic acids identified and quantified in the root exudates, 8 of them were significantly influenced by HM (e.g., salicylic and terephthalic acid). The transcriptional response of P. putida E36 was significantly affected by the HM addition to the growth medium, increasing the expression of several efflux pumps and stress response-related functional units. The additional supplementation of the growth medium with root exudates from HM-challenged plants resulted in a downregulation of 29% of the functional units upregulated in P. putida E36 as a result of HM addition to the growth medium. Surprisingly, root exudates + HM downregulated the expression of P. putida E36 functional units related to plant colonization (e.g., chemotaxis, motility, biofilm formation) but upregulated its antibiotic and biocide resistance compared to the control treatment without HM. Our findings suggest that HM-induced changes in root exudation pattern may attract beneficial bacteria that are in turn awarded with organic nutrients, helping them cope with HM stress. However, it might affect the ability of these bacteria to colonize plants growing in HM polluted areas. Those findings may offer an insight for future in vivo studies contributing to improvements in phytoremediation measures.