Influence of Substrates on the Surface Characteristics and Membrane Proteome of Fibrobacter succinogenes S85

Although Fibrobacter succinogenes S85 is one of the most proficient cellulose degrading bacteria among all mesophilic organisms in the rumen of herbivores, the molecular mechanism behind cellulose degradation by this bacterium is not fully elucidated. Previous studies have indicated that cell surface proteins might play a role in adhesion to and subsequent degradation of cellulose in this bacterium. It has also been suggested that cellulose degradation machinery on the surface may be selectively expressed in response to the presence of cellulose. Based on the genome sequence, several models of cellulose degradation have been suggested. The aim of this study is to evaluate the role of the cell envelope proteins in adhesion to cellulose and to gain a better understanding of the subsequent cellulose degradation mechanism in this bacterium. Comparative analysis of the surface (exposed outer membrane) chemistry of the cells grown in glucose, acid-swollen cellulose and microcrystalline cellulose using physico-chemical characterisation techniques such as electrophoretic mobility analysis, microbial adhesion to hydrocarbons assay and Fourier transform infra-red spectroscopy, suggest that adhesion to cellulose is a consequence of an increase in protein display and a concomitant reduction in the cell surface polysaccharides in the presence of cellulose. In order to gain further understanding of the molecular mechanism of cellulose degradation in this bacterium, the cell envelope-associated proteins were enriched using affinity purification and identified by tandem mass spectrometry. In total, 185 cell envelope-associated proteins were confidently identified. Of these, 25 proteins are predicted to be involved in cellulose adhesion and degradation, and 43 proteins are involved in solute transport and energy generation. Our results supports the model that cellulose degradation in F. succinogenes occurs at the outer membrane with active transport of cellodextrins across for further metabolism of cellodextrins to glucose in the periplasmic space and inner cytoplasmic membrane

Membrane resistance:The effect of salinity gradients over a cation exchange membrane

\u3cp\u3eIon exchange membranes (IEMs) are used for selective transport of ions between two solutions. These solutions are often different in concentration or composition. The membrane resistance (R\u3csub\u3eM\u3c/sub\u3e) is an important parameter affecting power consumption or power production in electrodialytic processes. In contrast to real applications, often R\u3csub\u3eM\u3c/sub\u3e is determined while using a standard 0.5M NaCl external solution. It is known that R\u3csub\u3eM\u3c/sub\u3e increases with decreasing concentration. However, the detailed effect of a salinity gradient present over an IEM on R\u3csub\u3eM\u3c/sub\u3e was not known, and is studied here using alternating and direct current. NaCl solution concentrations varied from 0.01 to 1.1M. The results show that R\u3csub\u3eM\u3c/sub\u3e is mainly determined by the lowest external concentration. R\u3csub\u3eM\u3c/sub\u3e can be considered as two resistors in series i.e. a gel phase (concentration independent) and an ionic solution phase (concentration dependent). The membrane conductivity is limited by the conductivity of the ionic solution when the external concentration, c\u3csub\u3eext\u3c/sub\u3eext≥0.3M, then differences of R\u3csub\u3eM\u3c/sub\u3e are small. A good approximation of experimentally determined R\u3csub\u3eM\u3c/sub\u3e can be obtained. The internal ion concentration profile is a key factor in modeling R\u3csub\u3eM\u3c/sub\u3e.\u3c/p\u3