"Isolement et caractérisation des bactéries capables de dégrader l'herbicide Glyphosate et optimisation des conditions de culture pour une dégradation plus efficace"

Abstract

"Glyphosate (N-phosphonomethylglycine) is the most commonly used herbicide worldwide. Because of concern regarding its toxicity, finding glyphosate-degrading microorganisms in soil is of interest. The success of this will depend on isolating bacteria with the ability to grow in presence of glyphosate. Seven bacterial strains were isolated from different untreated soils of Algeria, the strains were able to grow in a medium containing glyphosate as sole carbon or phosphorus source by enrichment cultures of these soils. Based on 16S rRNA gene sequence analysis, MALDI-TOF MS and biochemical properties. Five isolates were identified to the following species : Pseudomonas putida, Enterobacter cloacae, Rahnella aquatilis, Serratia marcescens and Enterobacter cloacae. The result of the MALDI TOF and the combined analysis of the gene sequences of the 16S rRNA with the rpoB gene allowed to approximate to the genus Enterobacter, the remaining two isolates designated Bisph1 Bisph2 and using glyphosate as the only phosphorus source. Multilocus sequence analysis (MLSA) of hsp60, rpoB, gyrB and DnaJ genes has shown that Bisph1 and Bisph2 form a distinct group in the phylogenetic tree of the genus Enterobacter. On the basis of the phenotypic characteristics and molecular analyses data we propose that strains Bisph1 and Bisph2 represent two novel species of the genus Enterobacter, for which the names Enterobacter biskrae sp. nov. and Enterobacter zibanae sp. nov. are proposed. This observation adds to the list of glyphosate-degrading bacteria. Pseudomonas putida and Enterobacter zibanae sp. nov. showed high levels of growth in the presence of glyphosate as sole phosphorus source , they have been used for studies of optimization of abiotic parameters for an efficient degradation of glyphosate. The best result of growth was on 1g/L of glyphosate in minimal medium at 150 rpm within 168 h, supplemented with glutamate with initial pH 9.0 at 30°C for P. putida and with east extract with an initial pH 9.0 at 37°C for E. zibanae sp. nov. The two isolates were able to tolerate up to 9 g/L of glyphosate. These results show that the bacterial strains may possess potential to be used in bioremediation of glyphosate-contaminated environments. The impact of glyphosate treatments on microbial community structure and function in vitro of two Algerian soils with different physicochemical properties (a forest soil and Saharan soil) were evaluated in the short term (30 days). Glyphosate was applied at a rate of 2.16 mg kg-1 of soil and microbial activity was assessed by soil basal respiration and microbial enumeration. Glyphosate addition to the forest soil had no effects on culturable microbial community and basal respiration. Unlike the forest soil, Saharan soil had a strong response in microbial activity and a marked increase in total culturable microorganisms. These initial findings suggest that glyphosate have no negative effects on microbial activity and it can improve soil quality."