Quantification of interactions between inhibitory primary and secondary substrates
Saez Ramila, Pablo Baldomero
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Permalink
https://hdl.handle.net/2142/21470
Description
Title
Quantification of interactions between inhibitory primary and secondary substrates
Author(s)
Saez Ramila, Pablo Baldomero
Issue Date
1990
Doctoral Committee Chair(s)
Rittmann, Bruce E.
Department of Study
Civil and Environmental Engineering
Discipline
Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Engineering, Sanitary and Municipal
Environmental Sciences
Language
eng
Abstract
The kinetic effects of the presence of one substrate on the degradation rate of the other substrate in a single-species, bisubstrate system were quantified in detail. The system consisted of a pure culture (Pseudomonas putida P$\sb{\rm p}$G4 (ATCC 17453)) transforming phenol and 4-chlorophenol simultaneously under fully aerobic conditions.
Phenol behaved as a self-inhibitory primary substrate, whose biodegradation rate when present as a single substrate could be modeled well using Haldane Kinetics. 4-chlorophenol behaved as a co-metabolite, because its transformation, observed at a significant rate, did not yield any increases in biomass.
When phenol and 4-chlorophenol were present together, the 4-chlorophenol- transformation rate was proportional to the phenol-oxidation rate, because the electrons required for the transformation of 4-chlorophenol were provided by the oxidation of phenol. In the absence of phenol, the 4-chlorophenol-transformation rate was proportional to the biomass-decay rate, because the required electrons were then provided by the biomass oxidation. These proportionalities in the rates clearly indicated that 4-chlorophenol transformation was possible only in the presence of a source of electrons, such as phenol or biomass.
4-chlorophenol inhibited phenol biodegradation. Two types of inhibitory effects were observed. For experiments with low initial 4-chlorophenol/phenol (I/S) ratios, the inhibition mainly decreased the Haldane qm$\sb{\rm s}$ parameter. On the other hand, the inhibition for high initial I/S ratios mainly was expressed by an increase to the Haldane K$\sb{\rm s}$ parameter for phenol. Similarly to the 4-chlorophenol-alone systems, the controlling variable for the type of inhibition observed in the bisubstrate system was the 4-chlorophenol/biomass ratio at the time when phenol oxidation stopped.
In summary, phenol was absolutely required for the transformation of 4-chlorophenol, because this transformation required electrons for regenerating the NADPH consumed. The requirement for phenol can be direct, manifested in the actual presence of phenol, or indirect, manifested in the cell mass grown previously when phenol was present (the cells acted as an electron reservoir in this case). 4-chlorophenol, in turn, was inhibitory to the degradation of phenol and to its own transformation.
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