Background
Clostridium cellulovorans
is a mesophilic, cellulosome-producing bacterium containing 57 genomic cellulosomal enzyme-encoding genes. In addition to cellulosomal proteins,
C. cellulovorans
also secretes non-cellulosomal proteins to degrade plant cell wall polysaccharides. Unlike other cellulosome-producing
Clostridium
species,
C. cellulovorans
can metabolize all major plant cell wall polysaccharides (cellulose, hemicelluloses, and pectins). In this study, we performed a temporal proteome analysis of
C. cellulovorans
to reveal strategies underlying plant cell wall polysaccharide degradation.
Results
We cultured
C. cellulovorans
with five different carbon sources (glucose, cellulose, xylan, galactomannan, and pectin) and performed proteome analysis on cellular and secreted proteins. In total, we identified 1895 cellular proteins and 875 secreted proteins. The identified unique carbohydrate-degrading enzymes corresponding to each carbon source were annotated to have specific activity against each carbon source. However, we identified pectate lyase as a unique enzyme in
C. cellulovorans
cultivated on xylan, which was not previously associated with xylan degradation. We performed
k
-means clustering analysis for elucidation of temporal changes of the cellular and secreted proteins in each carbon sources. We found that cellular proteins in most of the
k
-means clusters are involved in carbohydrate metabolism, amino acid metabolism, translation, or membrane transport. When xylan and pectin were used as the carbon sources, the most increasing
k
-means cluster contained proteins involved in the metabolism of cofactors and vitamins. In case of secreted proteins of
C. cellulovorans
cultured either on cellulose or xylan, galactomannan, and pectin, the clusters with the most increasing trend contained either 25 cellulosomal proteins and five non-cellulosomal proteins or 8–19 cellulosomal proteins and 9–16 non-cellulosomal proteins, respectively. These differences might reflect mechanisms for degrading cellulose of other carbon source. Co-abundance analysis of the secreted proteins revealed that proteases and protease inhibitors accumulated coordinately. This observation implies that the secreted protease inhibitors and proteases protect carbohydrate-degrading enzymes from an attack from the plant.
Conclusion
In this study, we clarified, for the first time, the temporal proteome dynamics of cellular and secreted proteins in
C. cellulovorans
. This data will be valuable in understanding strategies employed by
C. cellulovorans
for degrading major plant cell wall polysaccharides.
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