Calcium is a global regulator in Vibrio parahaemolyticus

Here we probe the global response to calcium in the marine bacterium and pathogen Vibrio parahaemolyticus by using transcriptome, reporter and phenotypic analyses. Swarming gene expression and motility were enhanced by calcium. Calcium also stimulated expression and function of one of the organism’s two type three secretion systems (T3SS1 but not the T3SS2). Although low calcium is an inducing signal for the T3SS of many organisms, calcium stimulation of T3SS has not been reported before. EGTA was also a stimulus for T3SS1 expression and activity; however this appeared to be the consequence of iron rather than calcium chelation. LafK, a key regulator of swarming genes, was found necessary for calcium induction of T3SS1 gene transcription and cytotoxicity. Regulation of swarming and T3SS1 were additionally linked by a negative feedback loop propagated by ExsA. Overexpression of exsA was used to probe the extent of the T3SS1 regulon and verify its coincident induction by calcium and EGTA. The calcium transcriptome analysis revealed a calcium-repressed LysR-type transcriptional regulator; CalR was shown to repress swarming and T3SS1 gene expression. Thus in V. parahaemolyticus, calcium influences gene expression and behavior and seems a signal pertinent for surface colonization and virulence. The gene expression profiles of Vibrio parahaemolyticus cells grown on rich medium or medium supplemented with CaCl2 or EGTA were compared using Affymetrix custom microarrays.