Regulatory mutations affecting the synthesis of cellulase in Pseudomonas fluorescens

Abstract

Pseudomonas fluorescens, was cultured in basal medium containing carboxymethyl-cellulose (CMC) as inducer 
and glucose or glycerol as carbon and energy sources. Ethylmethanesulphonate (EMS) was used to mutagenize 
the wild-type organism to produce mutants. The isolated mutants were screened for the isolation of catabolite 
repression resistant mutants in the presence of 1% (w/v) glucose as carbon source. A total of fifty mutants were 
isolated. All the mutants produced cellulase in the presence of CMC as an inducer with specific activity of 0.057, 
0.088 and 0.074 units/mg protein for the wild-type, catabolite repression resistant mutant4 (CRRmt4) and 
catabolite repression resistant mutant24 (CRRmt24), respectively. It was observed that addition of glucose or 
glycerol as carbon and energy sources to the culture medium resulted into considerable reduction in the 
cellulolytic activity. However, glycerol appeared to be a better carbon and energy source than glucose which 
inhibited enzyme expression in most of the strains used in this study. It was also observed that potent cellulase 
production occurred at the exponential growth phase of the organism. The isolated mutants were grouped into 
three classes based on their induction ratios namely; unimproved mutants, catabolite repression resistant 
mutants and mutants with highest induction ratio but sensitive to catabolite repression in the presence of high 
glucose concentration. The overall results obtained showed that cellulolytic activity in P. fluorescens was 
regulated by catabolite repression.