Fig. 1.

Siderophore production is an intermediate frequency trait in natural Vibrio populations. (A) The distribution of producers and nonproducers mapped onto the isolate phylogeny (Materials and Methods). The tree is based on the genetic marker hsp60 and comprises different genotypic clusters previously found to have cohesive ecology and hypothesized to represent samples from natural ecological populations. (B) Representation of the data shown in A in terms of percentage of producers descending from each internal node of the phylogeny. Among the populations with a high incidence of producers are animal host-associated V. ordalii and A. fischerii. The clade descending from node 3 corresponds to close relatives of V. splendidus (referred to as the V. splendidus-like group). Nodes 4, 5, and 6 correspond to the most recent common ancestors of V. crassostreae, V. cyclotrophicus, and V. splendidus. Within this large group, the patchy distribution of producers suggests that siderophore biosynthesis genes are rapidly gained and lost, possibly by recombination.