Isolation of Oxamyl-degrading Bacteria and Identification of cehA as a Novel Oxamyl Hydrolase Gene

Abstract

Microbial degradation is the main process controlling the environmental dissipation of the nematicide oxamyl. Despite that, little is known regarding the microorganisms involved in its biotransformation. We report the isolation of four oxamyl-degrading bacterial strains from an agricultural soil exhibiting enhanced biodegradation of oxamyl. Multilocus sequence analysis (MLSA) assigned the isolated bacteria to different subgroups of the genus Pseudomonas. The isolated bacteria hydrolyzed oxamyl to oxamyl oxime, which was not further transformed, and utilized methylamine as a C and N source. This was further supported by the detection of methylamine dehydrogenase in three of the four isolates. All oxamyl-degrading strains carried a gene highly homologous to a carbamate-hydrolase gene cehA previously identified in carbaryl- and carbofuran-degrading strains. Transcription analysis verified its direct involvement in the hydrolysis of oxamyl. Selected isolates exhibited relaxed degrading specificity and transformed all carbamates tested including the oximino carbamates aldicarb and methomyl (structurally related to oxamyl) and the aryl-methyl carbamates carbofuran and carbaryl which share with oxamyl only the carbamate moiety.

Expanded insecticide catabolic activity gained by a single nucleotide substitution in a bacterial carbamate hydrolase gene

“…It has been demonstrated before that minor amino acid substitutions can have determining effects on an enzyme's activity and substrate preference. In the case of melamine deaminase TriA and atrazine chlorohydrolase AtzA, a difference of only nine amino acids exists between these two enzymes but AtzA cannot recognize melamine and TriA cannot recognize atrazine (Seffernick et al, 2001). As for CfdJ, one amino acid change from glutamine in AtzA to aspartate in TriA at residue 125 has a determining effect on the enzyme's activity (dechlorination vs deamination) (Noor et al, 2012).…”

“…Between AtzA and TriA, just like in the case of CfdJ and CehA, only a single silent mutation is evident. This indicates that a strong selection pressure leads to the rapid changes in the amino acid composition that enables the organism to adapt to new substrates (Seffernick et al, 2001) as weak selection pressure often yields silent mutations that correct for codon bias (Jukes, 1980;Akashi, 1999). Noor et al (2014) recently showed that evolution of AtzA is ongoing by identifying AtzA homologues in different triazine degrading bacteria in which single amino acid substitutions determined triazine substrate range.…”

“…In addition to cehA from Rhi-zobium sp. AC100, close homologues (99% identity on amino acid level) of CfdJ are also present in a number of pseudomonads utilizing oxamyl as sole carbon source (Rousidou et al, 2016). The nucleotide sequences of the cfdJ homologues in those oxamyl degrading strains are either identical to this of cehA (in Pseudomonas monteilii OXA18) or differ from cehA at two nt positions (in Pseudomonas extremaustralis OXA17, Pseudomonas jinjuensis OXA20, and P. monteilii OXA25), i.e., a C-to-A transversion (resulting into a T-to-N substitution at amino acid position 477) in addition to the silent T$C transition (F498) also present in cfdJ.…”

The Plant as Metaorganism and Research on Next-Generation Systemic Pesticides – Prospects and Challenges

“…Polymer-lipid and other hybrid nanomaterials possessing different material properties such as hydrophobicity and water solubility should also be studied for SPs (Byrappa et al, 2008; Wu et al, 2012). Although the effect of soil applied pesticides on soil microbial community structure and rhizo-epiphytic microorganisms has been extensively studied, the effects on endophytic consortium and seed microbiome have to be studied further (Karpouzas et al, 2016; Rousidou et al, 2016). Knowledge on the interaction of SPs with endophytic microorganisms and their enzymatic activity can improve the efficacy of existing or new pesticides.…”

Microbial degradation of pesticide: A review

“…Four different strains of Pseudomonas were isolated from soil exhibiting enhanced oxamyl biodegradation. Bacteria could transform oxamyl to oxamin oxime by utilizing methylamine as a source of C and N. All of the four strains carried carbamate hydrolase homologue of the cehA gene (Rousidou et al, 2016). Carbamyl degrading bacteria; Bacillus, Morganella, Pseudomonas, Aeromonas and Corrynebacterium were isolated from local soil ecosystem of the Gaza strip.…”