Abstract
Fibrobacter succinogenes S85, isolated from the rumen of herbivores, is capable of robust lignocellulose degradation. However, the mechanism by which it achieves this is not fully elucidated. In this study, we have undertaken the most comprehensive quantitative proteomic analysis, to date, of the changes in the cell envelope protein profile of F. succinogenes S85 in response to growth on cellulose. Our results indicate that the cell envelope proteome undergoes extensive rearrangements to accommodate the cellulolytic degradation machinery, as well as associated proteins involved in adhesion to cellulose and transport and metabolism of cellulolytic products. Molecular features of the lignocellulolytic enzymes suggest that the Type IX secretion system is involved in the translocation of these enzymes to the cell envelope. Finally, we demonstrate, for the first time, that cyclic-di-GMP may play a role in mediating catabolite repression, thereby facilitating the expression of proteins involved in the adhesion to lignocellulose and subsequent lignocellulose degradation and utilisation. Understanding the fundamental aspects of lignocellulose degradation in F. succinogenes will aid the development of advanced lignocellulosic biofuels.
Highlights
Fibrobacter succinogenes S85, isolated from the rumen of herbivores, is capable of robust lignocellulose degradation
Our results indicate that the expression of these cellulases are regulated in response to the presence of cellulose and functionally confirm the role of the 10 up-regulated cellulases in the degradation of microcrystalline cellulose by F. succinogenes S85
The genome sequence of F. succinogenes S85 reflects the organism’s adaptation for lignocellulose degradation, as it encodes a variety of carbohydrate-degrading enzymes5
Summary
Fibrobacter succinogenes S85, isolated from the rumen of herbivores, is capable of robust lignocellulose degradation. Our results indicate that the cell envelope proteome undergoes extensive rearrangements to accommodate the cellulolytic degradation machinery, as well as associated proteins involved in adhesion to cellulose and transport and metabolism of cellulolytic products. It was found that the cellulolysis was much lower than that seen in F. succinogenes S85 This indicates that a synergistic mechanism of cellulolytic degradation is utilised by F. succinogenes S85. Neumann et al. employed transcriptomics to compare global expression of genes in F. succinogenes S85 when grown on glucose, cellobiose and cellulose They found distinct patterns of gene expression for genes encoding cellulases and hemicellulases when cells were grown on different carbon sources. Our research team was the first to employ cutting edge, gel-free semi-quantitative proteomics techniques to compare the differences in cell envelope proteome in F. succinogenes S85 when grown using glucose or cellulose as sole carbon sources. Several crucial mechanistic questions remain unanswered; What are the key proteins involved in lignocellulose degradation? How are these proteins organised? What are the processes that F. succinogenes S85 utilises to achieve complete degradation and utilisation of lignocellulose?
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