Fate of ¹⁴c‐labelled methomyl as affected by nostoc muscorum and tolypothrix tenuis and its role in their metabolic activities

Abstract

The insecticide methomyl inhibited the growth and total carbohydrate content of Nostoc muscorum and Tolypothrix tenuis, even at the lowest concentration (100 ppm) Glucose absorption and chlorophyll “a” content in Nostoc cells were retarded; while they increased in Tolypothrix. Carotene content was decreased in both cyanobacteria. Total nitrogen content of both organisms was significantly decreased whereas total nitrogen fixed, nitrogen released and protein content were increased in both organisms. The total phosphorus content of either cyanobacteria was sharply fluctuated, a trend that was reflected in similar effects of almost all phosphorus fractions. Although phosphorus uptake by Tolypothrix was increased, yet it was decreased in Nostoc especially 14 at lower and moderate concentrations. C‐labelled methomyl could be metabolized by both organisms. Of the total radioactivity recovered (89 and 85.6 % for Nostoc and Tolypothrix. respectively), the polar products accounted for about 25 %. TLC analysis revealed the presence of small amounts of two unknown metabolites with R_f values of 0.44 and 0.76. The ¹⁴C‐activity detected at R_f 0.44 is believed to be methyl mercaptan. Of the administered dose, about 15.0 % was found to be unextractable or bound compounds in both organisms.

Key words:

• ¹⁴C‐labelled methomyl
• Cyanobacteria
• Biochemical effects
• Metabolic degradation