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

Abstract

Production of cellulose has been thought to be restricted to a few bacterial species such as the model organism Acetobacter xylinus. We show by enzymatic analysis and mass spectrometry that, besides thin aggregative fimbriae, the second component of the extracellular matrix of the multicellular morphotype (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 rdar morphotype. Transcription of the bcs genes was not co‐expressed with the rdar morphotype under any of the environmental conditions examined. However, cellulose biosynthesis was turned on by the sole expression of adrA, a gene encoding a putative transmembrane protein regulated by agfD, indicating a novel pathway for the activation of cellulose synthesis. The co‐expression of cellulose and thin aggregative fimbriae leads to the formation of a highly hydrophobic network with tightly packed cells aligned in parallel in a rigid matrix. As the production of cellulose would now appear to be a property widely distributed among bacteria, the function of the cellulose polymer in bacteria will have to be considered in a new light.

Amyloid-Like Adhesins Produced by Floc-Forming and Filamentous Bacteria in Activated Sludge

“…This is in accordance with pure-culture studies performed on Salmonella enterica and E. coli, where amyloid fibers, cellulose, colanic acid, and other capsular polysaccharides are integrated to form a highly hydrophobic extracellular matrix under environmental stress (59,67,72). It also ties in with the suggestion that the amyloid is essential for biofilm formation and biofilm structure (49).…”

Comparative Genetics of the rdar Morphotype inSalmonella

“…An isogenic rpoS mutant strain of ATCC 14028 (⌬rpoS) and a pACYC/rpoS-complemented strain (⌬rpoSϩ) were included as controls for RpoS activity. (51,56,70). The air-liquid interface represents a favorable niche that provides bacterial cells with increased access to oxygen.…”

“…In E. coli, enhanced Tafi (curli) production has been linked to PagfD (PcsgD) mutations in the Ϫ10 region that move the sequence closer to the 70 consensus (62). The changes that occurred in Sarc4 and Sarc16 were also predicted to allow for 70 -based transcription of agfD. Sarc15 had properties similar to those of the revertant isolates and was also predicted to be RpoS deficient.…”

“…Virtually identical operons have also been identified in Escherichia coli and other enterobacterial species (8,49,69). In Salmonella, Tafi are produced together with cellulose (70), capsular and extracellular polysaccharides (17,26,67), and BapA (38), all of which come together to form a recalcitrant extracellular matrix that links individual cells together. Extracellular matrix production is associated with multicellular properties of Salmonella, both in the formation of the rdar morphotype (16,52) and in the formation of pellicles at the air-liquid interface in standing culture (51,56).…”

“…However, no activating signal has yet been identified. AgfD directly activates transcription of the agfBAC operon and adrA, which, in turn, activates cellulose biosynthesis (70). Salmonella capsular polysaccharide (26) and BapA (38) are also regulated by AgfD, but the exact mechanisms have not been determined.…”