Fig. 1
The cellulose biosynthesis operon, gene organization, proteins and functions. a Upper line Organization of the cellulose biosynthesis operon bcsEFG-bcsRQABZC in S. Typhimurium. bcsA and bcsB encode the cellulose synthase and bcsZ encodes a cellulase. bcsEFG and bcsR are characteristic for class II cellulose operons, while bcsQ is also found in class I operons [25]. Lower line Construction scheme of the non-polar bcsZ mutant using the tetRA gene cassette. b Detection of cellulase activity upon deletion and overexpression of BcsZ in S. Typhimurium UMR1 wildtype (WT). Bacterial cells were grown on carboxymethyl (CMC)-containing LB without salt agar plates. Yellow spots indicate cellulase activity through CMC degradation. Residual cellulase activity is seen in the wild type UMR1. BcsZ overexpression shows pronounced cellulase activity, abolished in the catalytic mutant BcsZE56A. Positive control E. coli DH5α pBcsZ and negative control E. coli DH5α VC. VC = pBAD30; pBcsZ = BcsZ cloned in pBAD30; pBcsZE56A = BcsZE56A cloned in pBAD30. c The cellulose secretion apparatus of S. Typhimurium modified after [25]. BcsA and BcsB form the active cellulose synthase complex. BcsC is supposed to be a pore in the outer membrane. BcsZ is a cellulase potentially located in the periplasm, but is found secreted in other cellulose producing/non-producing bacteria. Curli might aid the production of another unknown periplasmic/extracellular component requiring BcsZ. BcsE is a c-di-GMP binding protein required for optimal cellulose biosynthesis. The function of BcsF and BcsG is unknown. BcsQ and BcsR are also required for cellulose biosynthesis