Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Bacterial envelope proteins, so called surface layers (S-layer) are widely spread paracrystalline surface structures which coat the cells of lots of bacterial strains and as universal attribute of all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays on the cells as well as on surfaces and interfaces after their isolation. The S-layer proteins we investigate are from bacterial strains recovered from the uranium mining waste pile “Haberland” in Saxony, Germany. Their special S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce surface layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21 (DE3). Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM.
All methods demonstrated a total changed cell morphology. The cells formed long filaments in the beginning of the exponential growth stage and started to form 5-200 µm long tube like transparent structures at the end of the exponential growth stage, which contained E. coli single cells. These tube-like structures were isolated and analyzed by SDS-PAGE, N-terminal sequencing and infra red spectroscopy. The analyses showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanisms of these morphological changes are not known and will be analyzed in future. Investigations of supernatant proteins and proteins of periplasmic space in combination with enzyme assays demonstrate a transport of recombinant proteins that is not caused by cell damage. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.