Virulence in phage populations infecting Halobacterium cutirubrum
Abstract Phages of low virulence predominated culturable phage populations in a naturally occurring Jamaican salt pond with Halobacterium cutirubrum as host. These mutated rapidly in culture to higher virulence due to more rapid adsorption to host cells. Wild-type phages of low virulence, S50.2 and S41, with adsorption rate constants ( K ) of 1.15 and 1.21×10 −11 ml min −1 mutated to produce highly virulent derivatives S50.2Vm and S41Vm with K =2.60 and 2.61×10 −11 ml min −1 , values similar to the most virulent wild-type phages S5100 and S4100, K =2.61 and 2.55×10 −11 ml min −1 respectively. Quantitative measures of intracellular phage development were constant among low and high virulence wild-type and mutant phages S50.2, S5100 and S50.2Vm with eclipse periods of 5.5 h, latent periods of 9 h and average apparent burst sizes of 60–65. We propose that the natural environment may select for slow adsorption to reduce the frequency of release of DNA from phage particles in response to encounters with non-host material.