CATALASE-PEROXIDASE OF CAULOBACTER-CRESCENTUS - FUNCTION AND ROLE IN STATIONARY-PHASE SURVIVAL

Caulobacter crescentus is an obligate aerobe which is exposed to high concentrations of photosynthetic oxygen and low levels of nutrients in its aquatic environment, Physiological studies of oxidative and starv ation stresses in C. crescentus were undertaken through a study of lac Z fusion and null mutant strains constructed from the cloned 5' end of katG, encoding a catalase-peroxidase, The katG gene was shown to be s olely responsible fog catalase and peroxidase activity in C. crescentu s. Like the katG of Escherichia coli; C. crescentus katG is induced by hydrogen peroxide and is important in sustaining the exponential grow th rate, However, dramatic differences are seen in growth stage induct ion, E. coli KatE catalase and KatG catalase-peroxidase activities are induced 15- to 20-fold during exponential growth and then approximate ly halved in the stationary phase, In contrast, C. crescentus KatG act ivity is constant throughout exponential growth and is induced 50-fold in the stationary phase, Moreover, the survival of a C. crescentus ka tG null mutant is reduced by more than 3 orders of magnitude after 24 h in stationary phase and more than 6 orders of magnitude after 48 h, a phenotype not Seen for E. coli katE and katG null mutants, These res ults indicate a major role for C. crescentus catalase-peroxidase in st ationary-phase survival and raise questions about whether the peroxida tic activity as well as the protective catalatic activity of the dual- function enzyme is important in the response to starvation stress.