Novel surface layer protein genes in Bacillus sphaericus associated with unusual insertion elements


Novel surface layer protein genes in Bacillus sphaericus associated with unusual insertion elements

Pollmann, K.; Raff, J.; Schnorpfeil, M.; Radeva, G.; Selenska-Pobell, S.

The surface layer (S-layer) protein genes of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 and of its relative B. sphaericus NCTC 9602 were analyzed. The almost identical N-termini of both S-layer proteins possess a unique structure, comprising three Nterminal S-layer homologous domains (SLH). The central parts of the proteins share a high homology and are related to the S-layer proteins of B. sphaericus CCM 2177 and P-1. In contrast, the C-terminal parts of the studied S-layer proteins differ significantly between each other. Surprisingly, the C-terminal part of the S-layer protein of JG-A12 shares a high identity with that of the S-layer protein of B. sphaericus CCM 2177. In both strains the chromosomal S-layer protein genes were followed by a newly identified putative insertion element comprising three ORFs, which encode a putative transposase, a putative integrase/recombinase, a putative protein containing a DNA binding helix turn helix motif, and the S-layer protein-like gene copies sllA (9602) or sllB (JG-A12). Interestingly, both studied B. sphaericus strains were found to contain an additional, plasmid located and silent S-layer protein gene possessing the same sequence as sllA and sllB. The primary structures of the corresponding putative proteins are almost identical in both strains. The N-terminal and central parts of these S-layer proteins share a high identity with those of the chromosomally encoded functional S-layer proteins. Their C-terminal parts, however, differ significantly. These results strongly suggest that the S-layer protein genes have evolved via horizontal transfer of genetic information followed by DNA rearrangements mediated by mobile elements.

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Publ.-Id: 7517