Role of TapY1 and PlsB in Biofilm formation in aeromonas

Type IV pili in Aeromonas are involved in biofilm formation and colonization of biotic and aboitic surfaces. The tapY1 gene in Aeromonas encodes a type IV pili biogenesis protein. The ability of a tapY1 mutant of A. salmonicida strain 92 to be transformed is greatly reduced when compared to the wild type. In a microtiter plate biofilm assay, the tapY1 mutant showed an adhesion-deficient phenotype with an efficiency of only 37% of the wild-type A. salmonicida strain 92. In Aeromonas species, type IV pili play an important role in natural transformation and competence development. Type IV pili bind DNA in the competent cells and promote cell aggregation. Following growth for 8 hr, the highest concentration of extracellular DNA was found in the supernatant of the tapY1 mutant culture but was in association with the pelleted cells in the wild-type bacterial culture. The tapY1 mutant consistently showed higher concentrations of DNA in the supernatant than the wild type at different incubation times. Microscopic examination of the adhesion phenotype and biofilm formation revealed that the wild-type strain is able to make a stable attachment on the surface of the microtiter plate well and form a structured biofilm, whereas the tapY1 mutant showed no stable attachment on the abiotic surface. Since a previous study in our laboratory reported that the tapY1 mutant is greatly reduced in its ability to be transformed when compared to the wild-type, these results suggest that type IV pili in A. salmonicida strain 92 play a dual role in natural transformation and biofilm formation. This study also identified two other genes, by random transposon mutagenesis that play role in biofilm formation in A. hydrophila ATCC 7965. One gene encodes glycerol-3-phosphate acyltransferase (PlsB), which catalyzes the first step in phospholipid synthesis and is known to play a role in persister cell generation in Escherichia coli. The plsB mutant showed a partial biofilm-deficient phenotype, with an adhesion efficiency of 58% of the wild-type A. hydrophila ATCC 7965 strain. The other identified gene encodes a conserved hypothetical protein in A. hydrophila ATCC 7965. The conserved hypothetical protein mutant also showed an adhesion-deficient phenotype in the biofilm assay. This conserved protein of A. hydrophila ATCC 7965 shares the conserved domain of a pili assembly protein superfamily of Escherichia coli and Gram-negative pili assembly chaperone. Therefore, it can be assumed that this conserved hypothetical protein might have a role in pili assembly and biofilm formation in Aeromonas.