Differential expression of cellulases and xylanases by Cellulomonas flavigena grown on different carbon sources

The diversity of cellulases and xylanases secreted by Cellulomonas flavigena cultured on sugar cane bagasse, Solka-floc, xylan, or glucose was explored by two-dimensional gel electrophoresis. C. flavigena produced the largest variety of cellulases and xylanases on sugar cane bagasse. Multiple extracellular proteins were expressed with these growth substrates, and a limited set of them coincided in all substrates. Thirteen proteins with carboxymethyl cellulase or xylanase activity were liquid chromatography/mass spectrometry sequenced. Proteins SP4 and SP18 were identified as products of celA and celB genes, respectively, while SP20 and SP33 were isoforms of the bifunctional cellulase/xylanase Cxo recently sequenced and characterized in C. flavigena. The rest of the detected proteins were unknown enzymes with either carboxymethyl cellulase or xylanase activities. All proteins aligned with glycosyl hydrolases listed in National Center for Biotechnology Information database, mainly with cellulase and xylanase enzymes. One of these unknown enzymes, protein SP6, was cross-induced by sugar cane bagasse, Solka-floc, and xylan. The differences in the expression maps of the presently induced cultures revealed that C. flavigena produces and secretes multiple enzymes to use a wide range of lignocellulosic substrates as carbon sources. The expression of these proteins depends on the nature of the cellulosic substrate.