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Role of MshQ in MSHA pili biosynthesis and biofilm formation of Aeromonas hydrophila.

Biofilm formation of pathogen bacterium is currently one of the most widely studied topics; however, little is known regarding pathogen bacteria biofilms in aquaculture. Aeromonas hydrophila is a representative species of the genus Aeromonas, which has been recognized as a common pathogen, is associated with many diseases in aquatic animals, and causes significant mortality. The objectives of this study are i) to confirm that A. hydrophila can form biofilms on abiotic substrates and construct a biofilm growth curve for this bacterium; ii) to identify the genes that play crucial roles in A. hydrophila biofilm formation. The biofilm growth curve of A. hydrophila was constructed using a crystal violet assay, which showed that biofilm formation for this bacterium is a dynamic process. Next, a mutant library of pathogenic A. hydrophila B11 was constructed using the mini-Tn10 transposon mutagenesis system. A total of 861 mutants were screened, and 5 mutants were stably deficient in biofilm formation. Molecular analysis of the mutant B112 revealed that the open reading frame that encodes the protein MshQ was disrupted. Comparison of biological characteristics including growth, motility, and adhesion between the mutant B112 and the wild-type strain B11 suggested that MshQ is necessary for mannose-sensitive hemagglutinin pilus biosynthesis of A. hydrophila, and that these pili play crucial roles in A.hydrophila adherence to a solid surface during the early stages of biofilm formation.