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 m
ore rapid adsorption to host cells. Wild-type phages of low virulence,
S50.2 and S41, with adsorption rate constants (K) of 1.15 and 1.21x10
(-11) mi min(-1) mutated to produce highly virulent derivatives S50.2V
m and S41Vm with K = 2.60 and 2.61 x 10(-11) mi min(-1), values simila
r to the most virulent wild-type phages S5100 and S4100, K = 2.61 and
2.55 x 10(-11) mi min(-1) respectively. Quantitative measures of intra
cellular phage development were constant among low and high virulence
wild-type and mutant phages S50.2, S5100 and S50.2Vm with eclipse peri
ods of 5.5 h, latent periods of 9 h and average apparent burst sizes o
f 60-65. We propose that the natural environment may select for slow a
dsorption to reduce the frequency of release of DNA from phage particl
es in response to encounters with non-host material. (C) 1998 Federati
on of European Microbiological Societies. Published by Elsevier Scienc
e B.V.