Characterization of lignocellulose particles during lignocellulose solubilization by Clostridium thermocellum.

Clostridium thermocellum is a candidate bacterium for lignocellulose utilization due to its efficient lignocellulose solubilization ability. It has been reported that C. thermocellum efficiently degrades purified cellulose substrates, but cannot completely degrade milled lignocellulose powders. Evaluation of cellulose and hemicellulose contents in a lignocellulose residue after the cultivation of C. thermocellum indicated that C. thermocellum degraded cellulose and hemicellulose equally. Microscopic observations demonstrated that C. thermocellum significantly degraded small-sized lignocellulose particles, but it only partially degraded the larger sized particles. The lignin content of the large-sized particles was higher than that of the small particles. The remained large-sized particles included vascular tissues. These results suggest that the lignified structures such as vascular tissues in milled lignocellulose were less susceptible to bacterial lignocellulose solubilization.

A different pathway in the endoplasmic reticulum stress-induced expression of human HRD1 and SEL1 genes.

Human HRD1 and SEL1 are components of endoplasmic reticulum-associated degradation (ERAD), which is a retrograde transport mechanism from the ER to the cytosol for removing unfolded proteins. The expression of HRD1 and SEL1 was induced by ER stress-inducing agents and overexpression of both ER stress-responsive transcription factors, ATF6 and XBP1. Inhibition of IRE1 and ATF6 revealed that ER stress-induced HRD1 and SEL1 expressions are mediated by IRE1-XBP1- and ATF6-dependent pathways, respectively. These results suggest that the ER stress-induced ERAD gene expressions are mediated by different pathways, which are attributed to the differences in the promoter regions.