PHYSIOLOGICAL REGULATION OF COMPETENCE INDUCTION FOR NATURAL TRANSFORMATION IN ACINETOBACTER-CALCOACETICUS

Acinetobacter calcoaceticus induced competence for natural transformat ion maximally after dilution of a stationary culture into fresh medium . Competence was gradually lost during prolonged exponential growth an d after entrance into the stationary state. Growth cessation and nutri ent upshift were involved in the induction of competence. The level of competence of a chemostat culture of A. calcoaceticus was dependent o n the nature of the growth limitation. Under potassium limitation a tr ansformation frequency of +/- 1 x 10(-4) was obtained. This frequency was independent of the specific growth rate. In phosphate-, nitrogen-, and carbon-limited chemostat cultures, in contrast, the transformatio n frequency depended on the specific growth rate; the transformation f requency equalled +/- 10(-4) at dilution rates close to mu(max) of 0.6 h(-1) and decreased to +/- 10(-7) at a dilution rate of 0.1 h(-1). We conclude that (1) DNA uptake for natural transformation in A. calcoac eticus does not serve a nutrient function and (2) competence induction is regulated via a promoter(s) that resembles the fis promoter from E scherichia coli.