A continuous-flow culture selection experiment was designed to obtain mutants of strain PP3 capable of growing on 2-monochlorobutanoic acid (2MCBA), normally unable to act as a carbon and energy source for PP3. The experiment involved continuous exposure of PP3 to 2MCBA whilst the population's growth was supported by the metabolizable substrate, 2-monochloropropionic acid. The system failed to select for mutants able to grow on 2MCBA alone. However, the procedure resulted in the selection of two different strains of , namely, PP309 and PP310, both stably maintained as a mixed culture having excluded the parent strain. The two mutants differed significantly from PP3 with respect to their dehalogenating system since it was found that major changes in both dehalogenase specific activities and overall activity ratios had occurred. The dehalogenase system in strains PP309 and PP310 was inducible as in the parent strain. The results obtained were explained in terms of elevated production of fraction I dehalogenase compared with fraction II dehalogenase in the mutant strains in contrast to the parent strain. The results demonstrate that mutants may be selected showing altered enzyme activities in the absence of acquiring the capacity to grow solely on a novel substrate which provided the selection pressure.


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