Regulation system for protease production in Vibrio vulnificus

Vibrio vulnificus is a causative agent of serious food-borne diseases in humans related to consumption of raw seafoods. This human pathogen secretes a metalloprotease (VVP) that evokes enhancement of the vascular permeability and disruption of the capillaries. Production of microbial proteases is generally induced at early stationary phase of its growth. This cell density dependent regulation of VVP production in V. vulnificus known to be the quorum-sensing. When V. vulnificus was cultivated in Luria-Bertani (LB) medium, accumulation of the autoinducer, the signal molecule operating the quorum-sensing system, was detected. Moreover, expression of the vvp gene encoding VVP was found to be closely related with expression of the luxS gene that encode the synthase of the autoinducer precursor (luxS). These findings may indicate VVP production is controlled by the quorum-sensing system in LB medium. Futhermore, this system functioned more effectively at 26°C than at 37°C. When incubated at 37°C in human serum supplemented with ferric chloride, production of VVP and expression of vvp increased in proportion to the concentration of ferric ion; whereas, expression of luxS was not increased. This suggests that VVP production in human serum containing ferric ion may be regulated mainly by the system other than the quorum-sensing system.