Two soluble pyrophosphatases in Vibrio cholerae: transient redundancy or enduring cooperation?

Soluble pyrophosphatases (PPases), which are essential for cell life, comprise two evolutionarily unrelated families (I and II). Prokaryotic genomes generally contain a single PPase gene encoding either family I or family II enzyme. Surprisingly, four Vibrionales species, including the human pathogen Vibrio cholerae, contain PPase genes of both families. Here we show that both genes are transcriptionally active in V. cholerae, and encode functional PPases when expressed in Escherichia coli. In contrast, only the family I PPase protein is detected in V. cholerae under our experimental conditions. Phylogenetic analyses indicate that family II enzymes are not native to gamma-proteobacteria, but are of benefit to the marine species of this bacterial class. In this context, we favor the hypothesis that in the course of evolution, family II PPase was laterally transferred to the Vibrionales ancestor and partially degenerated due to functional redundancy, but nevertheless remained fixed as an adjunct to the family I enzyme.