Multisubstrate kinetics of PAH mixture biodegradation: analysis in the double-logarithmic plot

Abstract

The proposed method of kinetic analysis of aqueous-phase biodegradation of polycyclic aromatic hydrocarbons (PAH) mixture presupposes representation of kinetic curves for each pair of mixture components, S(x) and S(y), in double-logarithmic coordinates (ln S(x); ln S(y)). If PAH mixture conversion corresponds to the multisubstrate model with a common active site, then the graphs in double-logarithmic coordinates are straight lines with the angular coefficients equal to the ratio of respective first-order rate constants k(y)(x)= V(y)K(x)/K(y)V(x), where K(x) and K(y) are half-saturation constants, V(x) and V( y ) are the maximum conversion rates for substrates S(x) and S(y); the graph slope does not depend on any concentrations and remains constant during the change of reaction rates as a result of inhibition, induction/inactivation of enzymes or biomass growth. The formulated method has been used to analyze PAH mixture conversion by the culture of Sphingomonas sp. VKM B-2434. It has been shown that this process does not satisfy the multisubstrate model with a single active site. The results suggest that the strain VKM B-2434 contains at least two dioxygenases of different substrate specificity: one enzyme converts phenanthrene and fluoranthene and the other converts acenaphthene and acenaphthylene. The ratios of first-order rate constants have been obtained for these pairs of substrates.

Biodegradation of chemicals tested in mixtures and individually: mixture effects on biodegradation kinetics and microbial composition

“…Investigations conducted with enrichment consortia or individual microbial strains have shown that if a common enzymatic pathway for degradation exists, mixture effects can be positive (mixture enhances degradation of individual chemicals), because of stimulation of biomass growth and co-metabolism, or negative (mixture reduces degradation of individual chemicals), because of competitive inhibition leading to preferential degradation (Stringfellow and Aitken 1995;Guha et al 1999;Knightes and Peters 2006;Desai et al 2008;Baboshin and Golovleva 2011). Stimulation of biomass growth and competitive inhibition have been described by multisubstrate models (Guha et al 1999;Knightes and Peters 2006;Desai et al 2008).…”