Cometabolic degradation of thiocarbamate herbicides by Streptomyces sp. strain M2 and effects on the cell metabolism

The cometabolic degradation of thiocarbamate herbicides by Streptomyces sp. strain M2, has been investigated together with the effects of molinate on the cell physiology of the strain during the secondary metabolism. The phylogenetic position of the strain M2 was characterised by partial sequencing of the 16S rDNA. The sequence of 422 nucleotides at the 3' end of the 16S rDNA showed 97.196% identity with the rrnD of Streptomyces ambofaciens. When cultivated in a rich medium supplemented with 0.15 to 0.53 mM thiocarbamates, the strain M2 determined the disappearance of 30% of molinate in 80 h, 62% of EPTC in 168 h, 90% of cycloate in 168 h, 100% of butylate and pebulate in 96 and 216 h, respectively. In the presence of soybean flour, molinate degradation yield and rate were increased from 24.4 to 34.9 mg/μmol SF-420 and from 0.31 to 0.45 mg/μmol SF-420/h, respectively. Molinate disappearance occurred only at the onset of the stationary phase, affecting some aspects of the cell metabolism. The presence of increasing quantities of molinate determined in fact a progressive decrease of cellular ATP content during the stationary phase of the growth cycle. Moreover, in the presence of molinate, the strain M2 did not produce the red intracellular pigment normally produced after one week of growth.