Identification of multiple putative S-layer genes partly expressed by Lysinibacillus sphaericus JG-B53

Lysinibacillus sphaericus JG-B53 was isolated from the uranium mining waste pile Haberland near Johanngeorgenstadt, Germany. Previous studies have shown that many bacteria that have been isolated from these heavy metal contaminated environments possess surface layer proteins (S-layers) which enable the bacteria to survive by binding metals with high affinity. Conversely, essential trace elements are able to cross the filter layer and reach the interior of the cell. This is especially true of the S-layer of Lysinibacillus sphaericus JG-B53 which is therefore of high interest for both environmental studies and technical applications. Particularly the latter due to the high amounts isolatable from biomass and the outstanding recrystallisation and metal binding properties.
In this study, S-layer protein gene sequences encoded in the genome of L. sphaericus JG-B53 were identified using next generation sequencing (NGS) technology followed by bioinformatic analyses. The genome of L. sphaericus JG-B53 encodes at least 8 putative S-layer protein genes with distinct differences. Using mRNA analyses the expression of the putative S-layer protein genes was studied. The functional S-layer protein B53 Slp1 was identified as dominantly expressed S-layer protein in Lysinibacillus sphaericus JG-B53 by mRNA studies, SDS PAGE and N-terminal sequencing. B53 Slp1 is characterised by square lattice symmetry and a molecular weight of 116 kDa.
The S-layer protein B53 Slp1 shows a high similarity to the functional S-layer protein of Lysinibacillus sphaericus JG-A12, being isolated from the same uranium mining waste pile Haberland described by previous research. These similarities indicate horizontal gene transfer and DNA rearrangements between these bacteria. The presence of multiple S-layer gene copies may enable the bacterial strains to quickly adapt to changing environments.