Mineralization of Acephate, a Recalcitrant Organophosphate Insecticide Is Initiated by a Pseudomonad in Environmental Samples

An aerobic bacterium capable of breaking down the pesticide acephate (O,S-dimethyl acetyl phosphoramidothioic acid) was isolated from activated sludge collected from a pesticide manufacturing facility. A phylogenetic tree based on the 16 S rRNA gene sequence determined that the isolate lies within the Pseudomonads. The isolate was able to grow in the presence of acephate at concentrations up to 80 mM, with maximum growth at 40 mM. HPLC and LC-MS/MS analysis of spent medium from growth experiments and a resting cell assay detected the accumulation of methamidophos and acetate, suggesting initial hydrolysis of the amide linkage found between these two moieties. As expected, the rapid decline in acephate was coincident with the accumulation of methamidophos. Methamidophos concentrations were maintained over a period of days, without evidence of further metabolism or cell growth by the cultures. Considering this limitation, strains such as described in this work can promote the first step of acephate mineralization in soil microbial communities

Growth kinetics of <i>Pseudomonas sp.</i> Ind01 on acephate as a sole source of C, S and N.

<p>(a) Growth kinetics on MM1 (white squares), MM2 (black circles) and MM3 (black triangle) media, supplemented with 10 mM acephate. Growth on control MM1 medium w/o acephate is represented by open triangles. (b) Acephate degradation (solid lines, black marks) and methamidophos accumulation (dashed lines, white marks) during growth on MM1 (circles), MM2 (triangles) and MM3 (diamonds) media, supplemented with 10 mM acephate. The concentration of acephate in control uninoculated MM1 medium is represented by black squares. Each data point represents the average values and error bars are the standard deviation (n = 3).</p

Growth kinetics of <i>Pseudomonas sp.</i> Ind01 on MM1 growth media supplemented with additional carbon source.

<p>(a) Growth of Ind01 on MM1 medium supplemented with 10 mM acephate (black squares), 10 mM acephate and 10 mM sodium acetate (black triangles) or with no carbon source (white squares) (b) Growth of Ind01 on MM1 medium supplemented with 10 mM acephate (black squares). After culture reached stationary phase, 5 mM sodium acetate (black circles) or 5 mM sodium formate (white circles) was added as an additional carbon sources. Each data point is an average value and error bars represent the standard deviation (n = 2).</p

Growth kinetics of <i>Pseudomonas sp.</i> Ind01 on MM1 medium supplemented with acephate or methamidophos as a sole source of carbon.

<p>(a) Growth kinetics on MM1 medium, supplemented with 10 mM acephate (triangles), 10 mM methamidophos (circles), or without any carbon source (squares). (b) Concentration methamidophos (circles) and acephate (squares) in uninoculated (white) or inoculated (black) media. Average values and standard deviation (n = 2) are shown. Growth time is represented on an offset reciprocal scale.</p

Composition of minimal media used for isolation and characterization of acephate degrading bacterium.

<p>Composition of minimal media used for isolation and characterization of acephate degrading bacterium.</p