Abstract: The present invention is directed to a method of chemical addition to a microbial population to condition the population to (i) enhance bioconversion or biodegradation of a given substrate, or (ii) survive and perform greater bioconversion of a substrate when the population is exposed to fluctuating and in particular shock loads of the substrate. The method comprises conditioning the population by exposure of such to a non-toxic or non-inhibitory amount of a material which is biochemically or structurally similar to the substrate in question. The method is applicable in systems where the production of useful metabolites is the objective, as well as in waste treatment where degradation of a waste into more acceptable form is to be achieved.