Recombinant S-layer production induces disordered cell division in E. coli filaments

The rod-shaped bacterium Escherichia coli is one of the best studied microorganism with a size of 1.1-1.5 µm x 2.0-6.0 µm. We used E. coli BL21(DE3), one of the most widely used host in genetic engineering, for heterologous expression of surface layer (S-layer) proteins to enable a fast and efficient protein production.
S-layer are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelopes. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as filter materials or patterning structures in nanotechnology.
Surprisingly, the heterologous expression of S-layer proteins of the uranium mining waste pile isolate Lysinibacillus sphaericus JG-A12 induced drastic morphological changes of E. coli BL21(DE3) single cells to filaments and tubes enclosing single cells of >100 µm in length. The S-layer expressing E. coli cultures reached a high optical density and cells showed a high viability as well as strong expression of S-layer proteins. The drastically changed cell morphology was investigated by light microscope, AFM and TEM. Analyses with S-layer-GFP expressing cells, which were stained with DAPI and membrane stain, present a disordered cell division process. Our results give a new insight in the morphology and the cell division process in E. coli induced by recombinant proteins.

Lederer et al. (2010) Heterologous expression of the surface-layer-like protein SllB induces the formation of long filaments of Escherichia coli consisting of protein-stabilized outer membrane. Microbiology 156,3584-95.