Expression analysis and characterization of the mutant of a growth-phase- and starvation-regulated monofunctional catalase gene from Xanthomonas campestris pv. phaseoli

Analysis of the Xanthomonas campestris pv. phaseoli (Xp) catalase profile u sing an activity gel revealed at least two distinct monofunctional catalase isozymes denoted Kat1 and Kat2. Kat1 was expressed throughout growth, wher eas Kat2 was expressed only during the stationary phase of growth. The nucl eotide sequence of a previously isolated monofunctional catalase gene, Xp k atE, was determined. The deduced amino acid sequence of Xp KatE showed a hi gh percentage identity to an atypical group of monofunctional catalases tha t includes the well-characterized E. coli katE. Expression of Xp katE was g rowth phase-dependent but was not inducible by oxidants, In addition,growth of lip in a carbon-starvation medium induced expression of the gene. An Xp katE mutant was constructed, and analysis of its catalase enzyme pattern s howed that Xp katE coded for the Kat2 isozyme. yp katE mutant had resistanc e levels similar to the parental strain against peroxide and superoxide kil ling at both exponential and stationary phases of growth. Interestingly, th e level of total catalase activity in the mutant was similar to that of the parental strain even in stationary phase. These results suggest the existe nce of a novel compensatory mechanism for the activity of lip catalase isoz ymes. (C) 2000 Elsevier Science B.V. All rights reserved.