Fibrils as extracellular appendages of bacteria: Their role in contact-mediated cell-cell interactions in Myxococcus xanthus

Social behavior in the myxobacterium Myxococcus xanthus involves epicellular, peritrichous appendages called fibrils. These are polysaccharide organelles containing a set of tightly adhering proteins. It is proposed that cell-cell contact is perceived by the fibrils and is mediated by the action of a fibrillar ADP-ribosyl transferase. Fibrils or fibril-like organelles have also been found on a variety of other gram-negative bacteria and at least one archaeon, and may mediate cell-cell contact between the bacteria themselves or between the bacteria and their eukaryotic host cells.