A horizontally acquired cyclic di-GMP phosphodiesterase regulated by zinc and quorum sensing

Abstract

The second messenger cyclic di-GMP (cdG) in V. cholerae is indispensable for the regulation of biofilm formation, motility, and a variety of other important bacterial behaviors in the majority of bacteria. The human pathogen Vibrio cholerae has a diverse repertoire of diguanylate cyclase (DGC) and phosphodiesterase (PDE) enzymes that control the intracellular cdG concentration depending on local environmental cues and its physiological state. Determining the transcriptional regulation of these enzymes and the respective environmental signals that control their activity is important to understand how and when V. cholerae switches between motile and sessile lifestyles in different environments. In some strains of the current V. cholerae 7th pandemic El Tor biotype, the horizontally acquired Vibrio Seventh Pandemic 2 (VSP-2) island encodes an uncharacterized PDE at the gene locus vc0515 which we named zpdA (Zinc-inhibited Phosphodiesterase-A). We show here that zpdA transcription is repressed by Zur when Zn2+ is abundant, as well as by the quorum sensing regulator HapR when cells grow to high density. Furthermore, we find that the PDE activity of the purified ZpdA protein is inhibited by Zn2+ but is dependent on alternative divalent cations such as Mn2+, which we find is elevated in V. cholerae cells grown under zinc limiting conditions. We conclude that ZpdA is an active metal-dependent PDE that is regulated by Zn2+ availability at both the level of transcription and post-translation leading to elevated cdG levels when Zn2+ is abundant. Our results demonstrate the important role of metal availability in modulating cdG signaling in bacteria. ImportanceV. cholerae colonizes estuarine environments and human host where it transitions between motile to sessile states which are controlled by cdG levels. cdG levels change in response to a variety of signals and are controlled by the activity of DGCs and PDEs, enzymes that make and degrade cdG. In this work, we show that Zn2+ and the cell density regulator HapR repress ZpdA, the PDE present in the VSP-2 island, at the level of transcription, and that Zn2+unexpectedly alters the PDE activity of ZpdA protein itself. Our study highlights the role of metal availability as an important signaling cue that controls V. cholerae biology.