Catabolic enzyme levels in bacteria grown on binary and ternary substrate mixtures in continuous culture

Abstract

Bacteria grow on multicomponent substrates in most natural and engineered environments. To advance our ability to model bacterial growth on such substrates, axenic cultures were grown in chemostats at a low specific growth rate and a constant total energy flux on binary and ternary substrate mixtures and were assayed for key catabolic enzymes for each substrate. The substrates were benzoate, salicylate, and glucose, and the enzymes were catechol 1,2-dioxygenase, gentisate 1,2-dioxygenase, and glucose-6-phosphate dehydrogenase, respectively. The binary mixtures were salicylate with benzoate and salicylate with glucose. Measurements were also made of oxygen uptake rate by whole cells in response to each substrate. The effects of the substrate mixture on the oxygen uptake rate paralleled the effects on the measured enzymes. Catechol 1,2-dioxygenase exhibited a threshold response before synthesis occurred. Below the threshold flux of benzoate through the chemostat, either basal enzyme levels or nonspecific enzymes kept reactor concentrations too low for enzyme synthesis. Above the threshold, enzyme levels were linearly related to the fraction of the total energy flux through the chemostat due to benzoate. Gentisate 1,2-dioxygenase exhibited a linear response to the salicylate flux when mixed with benzoate, but a threshold response when mixed with glucose. Glucose-6-phosphate dehydrogenase activity increased in direct proportion to the glucose flux through the chemostat over the entire range studied. The results from two ternary mixtures were consistent with those from the binary mixtures.

The impact of feed composition on biodegradation of benzoate under cyclic (aerobic/anoxic) conditions

“…As Kovarova‐Kovar and Egli [9] postulated three strategies for the synthesis of catabolic enzymes by bacteria growing on a multicomponent substrate in continuous culture, the bacterial cultures in this study employed the second postulated strategy in dealing with mixtures of benzoate and pyruvate; that is, both the benzoate‐degrading capabilities and the in vitro activities of C23DO were in direct proportion to the flux through the chemostat of the substrate degraded by the pathway containing C23DO with some exceptions. Similar observations were made by Rudolph and Grady [23].…”

Relative Efficacy of Intrinsic and Extant Parameters for Modeling Biodegradation of Synthetic Organic Compounds in Activated Sludge: Steady‐State Systems

“…The kinetics of simultaneous biodegradation of multiple substrates is a complex issue (Kovárová-Kovar and Egli, 1998). For example, when a pure culture of bacteria is simultaneously degrading two substrates, the levels of degradative enzymes for each substrate depends on both the relative quantities of the substrates as well as their character (Kovárová-Kovar and Egli, 1998;Rudolph and Grady, 2002). However, in mixed culture systems like activated sludge, it is known that many substrates are degraded by only part of the community (Magbanua et al, 1998b), which implies that simultaneous substrate degradation may not be as widespread as one might think.…”

Stability of aerobic benzoate-degrading capability of Pseudomonas aeruginosa 142

“…cleavage enzymes during anaerobic starvation. Since the different types of microorganisms may express different types of aerobic ring-cleavage enzymes to break the stable benzene ring, aerobic ring-cleavage enzymes involved in the metabolism of benzoate in aerobic chemostat was screened and C12DO was the only aerobic ring-cleavage enzyme expressed as Rudolph and Grady [20] observed the activity of C12DO in P. aeruginosa 142 grown on benzoate aerobically. Thus, to be certain that the enzyme assays were working properly and with sufficient sensitivity, tests were performed with pure cultures known to express each of the key enzymes.…”