An experimental study of the population and evolutionary dynamics ofVibrio choleraeO1 and the bacteriophage JSF4

Abstract

Studies ofVibrio choleraein the environment and infected patients suggest that the waning of cholera outbreaks is associated with rise in the density of lytic bacteriophage. In accordance with mathematical models, there are seemingly realistic conditions where phage predation could be responsible for declines in the incidence of cholera. Here, we present the results of experiments with the El Tor strain ofV. cholerae(N16961) and a naturally occurring lytic phage (JSF4), exploring the validity of the main premise of this model: that phage predation limits the density ofV. choleraepopulations. At one level, the results of our experiments are inconsistent with this hypothesis. JSF4-resistantV. choleraeevolve within a short time following their confrontation with these viruses and their populations become limited by resources rather than phage predation. At a larger scale, however, the results of our experiments are not inconsistent with the hypothesis that bacteriophage modulate outbreaks of cholera. We postulate that the resistant bacteria that evolved play an insignificant role in the ecology or pathogenicity ofV. cholerae. Relative to the phage-sensitive cells from whence they are derived, the evolved JSF4-resistantV. choleraehave fitness costs and other characters that are likely to impair their ability to compete with the sensitive cells in their natural habitat and may be avirulent in human hosts. The results of thisin vitrostudy make predictions that can be tested in natural populations ofV. choleraeand cholera-infected patients.