Calcium and Iron Regulate Swarming and Type III Secretion in Vibrio parahaemolyticus

Abstract

Here, we probe the response to calcium during growth on a surface and show that calcium influences the transcriptome and stimulates motility and virulence of Vibrio parahaemolyticus. Swarming (but not swimming) gene expression and motility were enhanced by calcium. Calcium also elevated transcription of one of the organism's two type III secretion systems (T3SS1 but not T3SS2) and heightened cytotoxicity toward host cells in coculture. Calcium stimulation of T3SS gene expression has not been reported before, although low calcium is an inducing signal for the T3SS of many organisms. EGTA was also found to increase T3SS1 gene expression and virulence; however, this was demonstrated to be the consequence of iron rather than calcium chelation. Ectopic expression of exsA, encoding the T3SS1 AraC-type regulator, was used to define the extent of the T3SS1 regulon and verify its coincident induction by calcium and EGTA. To begin to understand the regulatory mechanisms modulating the calcium response, a calcium-repressed, LysR-type transcription factor named CalR was identified and shown to repress swarming and T3SS1 gene expression. Swarming and T3SS1 gene expression were also demonstrated to be linked by LafK, a 54 -dependent regulator of swarming, and additionally connected by a negative-feedback loop on the swarming regulon propagated by ExsA. Thus, calcium and iron, two ions pertinent for a marine organism and pathogen, play a signaling role with global consequences on the regulation of gene sets that are relevant for surface colonization and infection.

Quorum Sensing and Silencing in Vibrio parahaemolyticus

“…Chinese hamster ovary (CHO) cells (ATCC CCL-61) were used in coculture experiments as previously described (19). Briefly, the bacteria were grown overnight on HI plates at 30°C.…”

“…OpaR represses the expression of the lateral flagellar genes and induces cps expression (21,28). There is some evidence that OpaR regulates T3SS1 (26) and that regulation of swarming and T3SS gene expression are linked (19,20). In Vibrio harveyi, LuxR has been demonstrated to repress the T3SS; it does so by directly binding the regulatory region controlling the expression of exsA, which encodes the master transcriptional regulator of the T3SS (26,66).…”

Turnabout is fair play

“…1 Often times, their expression only commences after the bacteria receive specific environmental cues they encounter inside the host, such as elevated temperature, higher or lower than usual ion concentrations, or reactive oxygen species generated as a result of the induction of the host's immune response to infection. 2,3 In many cases, the pathogen's capacity to exert its full virulence is directly dependent on surface contact and therefore relies to a high degree on its ability to establish a stable interaction with the host cells. 4 For example, many pathogens express and secrete large autotransporter toxins into the surrounding medium.…”

Loss of Sigma Factor RpoN Increases Intestinal Colonization of Vibrio parahaemolyticus in an Adult Mouse Model

“…Additionally, sequence analysis of RIMD2210633, an O3:K6 isolate (TDH ϩ TRH Ϫ ), revealed the presence of two type 3 secretion systems (T3SS), one on each chromosome (T3SS-1 and T3SS-2) (16, 17). T3SS-1 is common to both clinical and nonclinical strains of V. parahaemolyticus and is a major contributor to cytotoxicity in in vitro models (18)(19)(20)(21)(22). T3SS-1 is the major contributor to lethality in the intraperitoneal mouse model, and it also plays a minor role in virulence in the infant rabbit model (23).…”