THE SWEET TOOTH OF FLAVOBACTERIUM- GLIDING IS AFFECTED BY PLANT OLIGOSACCHARIDES

Members of the Bacteroidetes phylum, especially the Flavobacterium genus, are highly abundant in rhizosphere of a wide array of plants where they may compose up to 20% of total defined bacterial genera. Several studies have demonstrated that certain Flavobacteria strains serve as microbial biocontrol agents that contribute to plant health and immunity. The Bacteriodetes phylum has a gliding motility not related to other forms of bacterial movement, and a unique type IX secretion system and these two systems share mutual molecular components.

To investigate factors potentially involved in Flavobacterium recruitment to the root surface, we examined the capacity of various plant-derived sugars to stimulate flavobacterial motility. Our results revealed that the plant cell wall-associated polysaccarides pectin and glucomannan induce proliferation and gliding motility of three different flavobacterial strains F. johnsoniae, Flavobacterium sp. F52 and LOA5, whereas xylan, xyloglucan, arabinose cellulose and glucose did not. In addition, this chemotactic-like phenomenon did not occur in gliding defective mutants of strains F. johnsoniae and Flavobacterium sp. F52. We also found that gliding toward pectin was dose dependent as bacteria spread less on lower pectin concentrations. F. johnsoniae and Flavobacterium sp. F52 were able to grow on pectin as a single carbon source both in liquid and solid media, but the chemotactic-like phenomenon was primarily observed on rich media. Our results demonstrate that specific plant cell wall-associated polysaccarides can serve as a signal to activate or enhance gliding in Flavobacterium strains and possibly serve as an environmental proxy that stimulates colonization of plant root surfaces. Future studies are needed to find the exact signaling pathway and molecular components by which pectin and glucomannan activate gliding in flavobacteria.