Diverse horizontally transferred cellulose biosynthesis gene clusters in Escherichia coli strains
The phosphoethanolamine modified exopolysaccharide cellulose is a major extracellular matrix component of Escherichia coli and Salmonella typhimurium. Upon enhanced acute virulence, however, cellulose production can be diminished or entirely abolished. Here, we report that homologs of the bcsABC core genes of the core genome bcs cellulose biosynthesis operon and even entire bcs operons can be mobilized on plasmids and are occasionally manifested on E. coli chromosomes at alternative locations. While BcsA2 and BcsA3 cellulose synthases are restricted to the genus Escherichia, the BcsA4 cellulose synthase and the entire associated bcs gene cluster are highly similar to one of the two chromosomal bcs gene clusters harboured by Klebsiella pneumoniae. Cyclic di-GMP turnover proteins known to post-translationally regulate cellulose biosynthesis are frequently localized on bcs operon bearing plasmids. In thermotolerant meat derived E. coli 740v1 harbouring a type 4 bcs operon on a plasmid, chemical and genetic evidence indicates that cellulose is produced in M9 minimal medium and upon activation by the second messenger cyclic di-GMP, an allosteric activator of the cellulose synthase, respectively. With gene duplication and horizontal gene transfer to contribute to the multiplication of bcs operons in a number of different bacterial species, the ecological role(s) of multiplication, transfer and replacement of cellulose biosynthesis operons also in species other than E. coli still need to be unraveled.