Comparison of microcolony formation between Vibrio sp. strain S141 and a flagellum-negative mutant developing on agar...

A flagellum-negative mutant, M8.2, of the marine bacterium Vibrio sp. S141 was produced by transposon mutagenesis. Time-lapse video imaging of surface colonisation behaviour and microcolony formation of S141 compared to M8.2 cells was carried out to investigate the role of the flagellum of Vibrio sp. S141 in microcolony formation on agar and glass substrata. On an agar surface, S141 cells formed a tetrad pattern after the first two cell divisions, during initial surface colonisation. Developed microcolonies consisted of tight circular arrangements of cells with infrequent branching of cells from the main body. In contrast, M8.2 cells did not form tetrad patterns and micro-colonies generally showed enhanced branching and did not develop circular arrangements of cells. On a glass surface under flow conditions, S141 cells displayed several types of movement behaviours at the surface which may have assisted microcolony formation. M8.2 cells appeared unable to develop micro-colonies, but rather displayed a behaviour which enabled them to spread out across the substratum. Laser scanning confocal microscopy revealed S141 mature biofilms consisted of characteristic towers of bacterial growth with scattered troughs. The flagellum-negative M8.2 biofilm did not form such architecture, displaying a homogeneous distribution of cells throughout the biofilm and across the entire substratum. Although not required for attachment to the glass substratum, the flagellum was required for alignment as well as specific movement behaviours by S141 cells.