Clostridium thermocellum Cel5L – Cloning and Characterization of a New, Thermostable GH5 Cellulase.

Aims: Clostridium thermocellum is a thermophilic, anaerobic bacterium that ferments cellulose and produces ethanol. While many of the predicted cellulases have been characterized from C. thermocellum, characterization of additional members is still needed to unravel the function of these enzymes. Study Design: This report describes the first cloning, expression, characterization, and evaluation in cellulose degradation of Clostridium thermocellum Cel5L as well as its relationship to other cellulases. Results: Cel5L, a 526 amino acid protein that shows low homology to other cellulases of C. thermocellum, possesses both endo and exo activity on -glucan, carboxymethylcellulose, and cellooligosaccharides; the enzyme does not hydrolyze xylan, xyloglucan or glucomannan. When combined with exo-cellulases and -glucosidase, Cel5L generates more glucose from cellulose than other tested C. thermocellum GH5 cellulases, which is surprising due to the lack of an annotated carbohydrate binding module. The Cel5L phylogenetic tree shows orthologs in both mesophilic and thermophilic cellulose degraders. Conclusion: The presence of these orthologs in a variety of molecular constructs demonstrates the importance of Cel5L and its orthologs in cellulose degradation, both in C. thermocellum as well as other gram-positive cellulose degraders.

Sporogenesis and development of gametophytes in an endangered plant, Tetracentron sinense Oliv

The sporogenesis and development of gametophytes in Tetracentron sinense Oliv. were studied with light microscopy. The anther has four microsporangia; its primary anther wall consists of an epidermis, an endothecium, one or two middle layers and one glandular tapetum. Simultaneous cytokinesis follows meiosis, forming a tetrahedral tetrad. Mature pollen grains are two-celled at the time of anther dehiscence. Its ovule is anatropous, bitegmic and crassinucellate; the development of the female gametophyte is of the monosporic 8-nucleate Polygonum type. Significantly, some striking features were first found in T. sinense: (1) anther dehiscence occurs soon after the endothecium fibrously thickens and the intersporangial septum degenerates; (2) tapetum degeneration is retarded, persisting up to the stage of two-celled pollen grain; (3) a few cellular events such as the vacuolization and the contraction and deformation of the pollen mother cell (PMC) and microspore are not normal at the PMC, dyad and tetrad stages. The abnormalities during male reproduction might be one of important factors resulting in the poor natural regeneration of T. sinense.