Quantitative modelling of crude oil toxicity using the approach of cybernetics and structured mechanisms of microbial processes.

Cybernetics and structured approach to biochemical processes in microbial cells offer the status of using various cell components of Azotobacter as molecular markers in toxicity assay of environmental toxicants. The intra-linked dynamic physicochemical reactions of the basic macromolecules--DNA, protein and membrane lipids--with respect to the crude oil in the growth environment, results in an 'impulse transfer function'. The structured effects are reduction in both DNA and protein levels, and an elevated level of lipid peroxidation products. Toxicity index (Ti) of the crude oil, at a given concentration, is the percent ratio of the summation of the products of these effect parameters' and their respective weightings, relative to control. The EC50 is the effective percent (w/v) concentration of the crude oil at which a toxicity index of 50% was recorded, and this corresponded with about 44% loss in nitrogen fixation of the diazotrophic bacterium.