The multicellular morphotypes of Salmonella typhimurium and Escherichia coli produce cellulose as the second component of the extracellular matrix

Production of cellulose has been thought to be restricted to a few bacteria l species such as the model organism Acetobacter xylinus. We show by enzyma tic analysis and mass spectrometry that, besides thin aggregative fimbriae, the second component of the extracellular matrix of the multicellular morp hotype (rdar) of Salmonella typhimurium and Escherichia coli is cellulose. The bcsA, bcsB, bcsZ and bcsC genes responsible for cellulose biosynthesis are not regulated by AgfD, the positive transcriptional regulator of the rd ar morphotype. Transcription of the bcs genes was not co-expressed with the rdar morphotype under any of the environmental conditions examined. Howeve r, cellulose biosynthesis was turned on by the sole expression of adrA, a g ene encoding a putative transmembrane protein regulated by agfD, indicating a novel pathway for the activation of cellulose synthesis. The co-expressi on of cellulose and thin aggregative fimbriae leads to the formation of a h ighly hydrophobic network with tightly packed cells aligned in parallel in a rigid matrix. As the production of cellulose would now appear to be a pro perty widely distributed among bacteria, the function of the cellulose poly mer in bacteria will have to be considered in a new light.