Cellulose biosynthesis operon

THE CELLULOSE BIOSYNTHESIS OPERON IN Salmonella typhimurium AND Escherichia coli... 

Figure 7-2. Structure of the cellulose biosynthesis operon bcs in Salmonella typhimurium and Escherichia coli. Arrowheads represent the open reading frames (ORFs). Symbols above the ORFs show overlap of (D) or distance between (A) ORFs in bps. Symbols below the ORFs show insertions (A) or deletions (V), which occur in S. typhimurium LT2 as compared to Escherichia coli K-12. Closed arrow5 just above the ORFs indicate transposon insertions in bcsA and bcsC. The larger arrow indicates the position of the transposon used to study transcriptional regulation of the respective gene. The table summarizes the features of bcs genes using the positioning in the genome of the sequenced LT2 strain. The start codon proposed for bcsC in E. Coli K-12 leads to a shorter ORF (bcsC ).

When compared to the classical type 1 cellulose biosynthesis operon of Glu-conacetobacter xylinus that produces the cellulose I allomorph under laboratory conditions the cellulose biosynthesis operons of Salmonella spp. and E. coli have both, homologous and unique components (Figure 7-3). As in G. xylinus bcsA, which encodes for the catalytic subunit of the cellulose synthase, and bcsB, which... 

BcsQ which is required for cellulose biosynthesis in vivo, is part of the cellulose biosynthesis operon in Enterobacteriaceae and G. xylinus. BcsC contains a N-terminal membrane domain and several tetratrico peptide repeats (TRPs) motifs, indicating that it might participate in protein-protein interactions. 

A regulatory cascade leading to the activation of cellulose biosynthesis has been established in S. typhimurium (Figure 7-4a). In plate-grown cells, which harbor an intact cellulose biosynthesis operon, expression of AdrA from a low copy number plasmid is sufficient to initiate temperature independent cellulose biosynthesis (Zogaj et al. 2001). 

OCCURRENCE OF THE CELLULOSE BIOSYNTHESIS OPERON AMONG ENTEROBACTERIAL SPECIES... 

The proliferation of complete genome sequences in public databases provides an additional means to track the evolution of cellulose in bacteria. Conservation of operons and/or gene clusters (synteny) can be used to trace not only the history of cellulose synthase, but also its associated proteins. The existence of a few these gene clusters has been well documented. In the sections below, I would like to give a brief review of the known gene organizations and introduce two novel ones which may be linked to the eukaryotic acquisition of cellulose biosynthesis. 

Figure 7-4. (a) The cellulose biosynthesis module with regulatory units. Cellulose biosynthesis is activated by the direct or indirect interaction of the AdrA protein with gene products from the bcs operons. Transcription of odrA is conducted by CsgD together with the second principal sigma factor in stationary phase, RpoS. 

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