The cellulosome is a supramolecular multienzyme complex formed via species-specific interactions between the cohesin modules of scaffoldin proteins and the dockerin modules of a wide variety of polysaccharide-degrading enzymes. Here, we report a comparative analysis of cellulosomes prepared from the thermophilic anaerobic bacteria Clostridium (Ruminiclostridium) clariflavum DSM 19732 and Clostridium (Ruminiclostridium) thermocellum ATCC 27405 grown on delignified rice straw. The results indicate that the isolated C. clariflavum cellulosome exhibits lower activity for insoluble cellulosic substrates and higher activity for hemicellulosic substrates, especially for xylan, compared to the isolated C. thermocellum cellulosome. The C. clariflavum cellulosome was separated into large and small complexes by size exclusion chromatography, and the high xylanase activity of the intact complex is mainly attributed to the small complex. Furthermore, both C. clariflavum and C. thermocellum cellulosomes efficiently converted delignified rice straw into soluble sugars with different compositions, whereas a mixture of these cellulosomes exhibited essentially no synergy for the saccharification of delignified rice straw. This is the first study to report that isolated C. clariflavum cellulosomes exhibit greater xylanase activity than isolated C. thermocellum cellulosomes. We also report the effect of a combination of intact cellulosome complexes isolated from different species on the saccharification of plant biomass.

Serine-type phage integrases catalyze unidirectional site-specific recombination between the attachment sites, attP and attB, in the phage and host bacterial genomes, respectively; these integrases and DNA target sites function efficiently when transferred into heterologous cells. We previously developed an in vivo site-specific genomic integration system based on actinophage TG1 integrase that introduces ∼2-kbp DNA into an att site inserted into a heterologous Escherichia coli genome. Here, we analyzed the TG1 integrase-mediated integrations of att site-containing ∼10-kbp DNA into the corresponding att site pre-inserted into various genomic locations; moreover, we developed a system that introduces ∼10-kbp DNA into the genome with an efficiency of ∼10(4) transformants/μg DNA. Integrations of attB-containing DNA into an attP-containing genome were more efficient than integrations of attP-containing DNA into an attB-containing genome, and integrations targeting attP inserted near the replication origin, oriC, and the E. coli "centromere" analogue, migS, were more efficient than those targeting attP within other regions of the genome. Because the genomic region proximal to the oriC and migS sites is located at the extreme poles of the cell during chromosomal segregation, the oriC-migS region may be more exposed to the cytosol than are other regions of the E. coli chromosome. Thus, accessibility of pre-inserted attP to attB-containing incoming DNA may be crucial for the integration efficiency by serine-type integrases in heterologous cells. These results may be beneficial to the development of serine-type integrases-based genomic integration systems for various bacterial species.