Vibrio cholerae O1 is the etiological agent of cholerae, a severe diarrhoeal disease acquired by contamined food or water. Adhesion to surfaces and formation of a biofilm, both in the human intestine and in aquatic surroundings, play an important role in Vibrio cholerae’s success as a pathogen and as an environmental organism.
To survive in such distinct environments bacterial cells must regulate gene expression, in many cases, with the involvement of two component systems such as PhoB/PhoR, that controls expression of Pho regulon genes in response to low inorganic phosphate (Pi) levels in the media. PhoB is a response regulator that binds to the promoter regions of the Pho regulon genes and activate their trasncription under Pi starvation.
In this work we analyzed the ability of classical (O395 and 569B) and El Tor (N16961) strains of V. cholerae O1 and two isogenic phoB mutants, to form biofilm under a variety of conditions. Biofilm assays were carried out in microtitre dishes wich were incubated without shaking for 24 h. The biofilm adhered to the surface was stained with crystal violet solution. After that the wells were washed out and the biofilm was immediately disrupted with dimethyl sulphoxide (DMSO). Optical density of the solution was measured at 570nm.
Biofilm formation was investigated at 22º 30ºand 37ºC in defined medium (Tris-glucose/salts, TG) supplemented with Pi at low (LP) and high (HP) concentrations. The effect of a detergent, sodium deoxycholate (DOC) on the biofilm formation by the strains in the above media was also tested. The data were analyzed by the program Statistica 5.0 and showed that biofilm was equally produced by all the strains in TGHP and TGLP in all temperatures.
DOC, at three different concentrations, affected biofilm formation by the strains in both TGHP and TGLP at 22, 30 and 37ºC. In general, biofilm formation increased with crescent concentrations of DOC in both media, but the optimum temperature varied with the strain. Curiously, the phoB mutants always formed more biofilm than the wild-type in all conditions tested, but maintained the same pattern of formation of the parental strain. The likely involvement of the phoB in biofilm formation by the strains is under investigation.