Differences in biomass degradation between newly isolated environmental strains of Clostridium thermocellum and heterogeneity in the size of the cellulosomal scaffoldin

Abstract

Cellulolytic bacterial strains with high activity were isolated from cellulose degrading enrichment cultures derived from thermophilic biogas plants and environmental samples. The 16S rRNA gene sequences of the strains revealed >99.8% sequence identity and affiliation with the species Clostridium thermocellum. The strains differed in their ability to degrade crystalline cellulose, especially at an elevated temperature of up to 67°C and at relatively low pH values (pH 6.5). To evaluate the influence of amino acid sequences on the discrepancies in cellulose degradation efficacy, the gene for the major cellulosomal component CelR was sequenced for all strains. The sequences were found to be almost identical (>99%). In contrast, the cellulosomal scaffoldin gene cipA showed more differences in the amino acid sequence and contained 8 or 9 cohesin modules, which indicated a different size of the cellulosome depending on the isolate. Based on MALDI-TOF MS analysis the relative abundance of important cellulosomal enzyme classes was determined. The strains with better biomass degradation properties (BC1 and NB2) had a significantly higher fraction of xylanases.