Résumé:
"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."
