RecA-dependent viral burst in bacterial colonies during the entry into stationary phase

We have explored the nature of the sudden viral amplification observed during the ageing of P22-infected lysogenic colonies of Salmonella typhimurium [Ramírez, E, and Villaverde, A. (1997) Gene 202, 147-149]. By a comparative analysis of the wild-type P22 and a P22 integration mutant, it has been shown that the conditions promoting prophage induction occur in only a small portion of the bacterial population and briefly during the transition between the exponential growth and the stationary phase. The viral burst is RecA-dependent and cannot be reproduced in continuous culture by a mere decrease of the growth rate. This suggests that the limited viral propagation in colonies is probably linked to heterogeneous physiological conditions within colonial populations, distinct from those of the homogeneous liquid cultures.