Cometabolism
(Biological Processe)
Tech
What is Cometabolism?
Cometabolism is defined as the simultaneous degradation of two compounds, in which the degradation of the second compound (the secondary substrate) depends on the presence of the first compound (the primary substrate). This is in contrast to simultaneous catabolism, where each substrate is catabolized concomitantly by different enzymes. Cometabolism occurs when an enzyme produced by an organism to catalyze the degradation of its growth-substrate to derive energy and carbon from it is also capable of degrading additional compounds. The fortuitous degradation of these additional compounds does not support the growth of the bacteria, and some of these compounds can even be toxic in certain concentrations to the bacteria. The first report of this phenomenon was the degradation of ethane by the species Pseudomonas methanica. These bacteria degrade their growth-substrate methane with the enzyme methane monooxygenase (MMO). MMO was discovered to be capable of degrading ethane and propane, although the bacteria were unable to use these compounds as energy and carbon sources to grow. Another example is Mycobacterium vaccae, which uses an alkane monooxygenase enzyme to oxidize propane. Accidentally, this enzyme also oxidizes, at no additional cost for M. vaccae, cyclohexane into cyclohexanol. Thus, cyclohexane is co-metabolized in the presence of propane. This allows for the commensal growth of Pseudomonas on cyclohexane. The latter can metabolize cyclohexanol, but not cyclohexane.