Colony spreading of the gliding bacterium Flavobacterium johnsoniae in the absence of the motility adhesin SprB

Abstract

Colony spreading of Flavobacterium johnsoniae is shown to include gliding motility using the cell surface adhesin SprB, and is drastically affected by agar and glucose concentrations. Wild-type (WT) and ΔsprB mutant cells formed nonspreading colonies on soft agar, but spreading dendritic colonies on soft agar containing glucose. In the presence of glucose, an initial cell growth-dependent phase was followed by a secondary SprB-independent, gliding motility-dependent phase. The branching pattern of a ΔsprB colony was less complex than the pattern formed by the WT. Mesoscopic and microstructural information was obtained by atmospheric scanning electron microscopy (ASEM) and transmission EM, respectively. In the growth-dependent phase of WT colonies, dendritic tips spread rapidly by the movement of individual cells. In the following SprB-independent phase, leading tips were extended outwards by the movement of dynamic windmill-like rolling centers, and the lipoproteins were expressed more abundantly. Dark spots in WT cells during the growth-dependent spreading phase were not observed in the SprB-independent phase. Various mutations showed that the lipoproteins and the motility machinery were necessary for SprB-independent spreading. Overall, SprB-independent colony spreading is influenced by the lipoproteins, some of which are involved in the gliding machinery, and medium conditions, which together determine the nutrient-seeking behavior.

Biofilm Spreading by the Adhesin-Dependent Gliding Motility of Flavobacterium johnsoniae. 1. Internal Structure of the Biofilm

“…The attachment of colonies to a solid surface is a complex process mediated by cell-cell interactions. For F. johnsoniae, this process was affected by the cell surface components and environmental factors, such as the nutrient supply and moisture (Figures 1-5) [16]. Biofilms of many bacteria, such as P. aeruginosa and E. coli, are surface-attached microbial communities composed of cells embedded in an extracellular polymeric matrix (EPM) [36,37].…”

“…Our data suggest that gliding movement is associated with the volume of extracellular matrix, and thus affects the maturation of biofilm architecture. Recently, we investigated the SprB-independent colony spreading of F. johnsoniae on soft agar containing glucose [16]. The extracellular matrix of the colony contained a network of extracellular fibers and many secreted vesicles, which is similar with that on 1% A-PY2 [16,50].…”

“…Consequently, the thick fiber-containing EPM might include double-stranded DNA filaments and extracellular polysaccharides, as observed in the biofilms of S. aureus and P. acnes immersed in aqueous liquid by atmospheric scanning electron microscopy (ASEM) [45,46]. Further experiments are required to understand the water-rich architecture of F. johnsoniae biofilms, for example, using ASEM that enabled observations of various water-rich phenomena of organic and inorganic substances at high resolution [16,51,52]. The undulations observed for the layered surface coats of F. johnsoniae cells in biofilm has a possibility to be artefacts, due to the dehydration pretreatment of the Epon-embedded TEM.…”

“…To visualize the movement of single bacterial cells at the colony edge, a 1:100 mixture of WT cells with and without cytoplasmic GFP expression was inoculated in the center of an agar plate, incubated for 24 h, and visualized by time-lapse fluorescence microscopy ( Figure S2a) [16,35]. This video (at 300× the speed of standard time-lapse fluorescence microscopy imaging) is shown in Figure S2a.…”

“…Colony spreading of F. johnsoniae is influenced by modifications of the motility machinery complex, such as SprB deficiency, and by environmental factors, such as temperature and nutrient availability [16]. When cultured on nutrient-poor agar medium, gliding cells of F. johnsoniae form thin film-like spreading colonies [2].…”