Animal cellulases

Abstract

Previous dogma has maintained that cellulose, ingested by xylophagous or herbivorous animals, is digested by cellulolytic symbiotes. The first evidence in conflict with this contention involved the demonstration of cellulolytic activities in symbiote-free secreting organs (e.g., the salivary glands of termites) or defaunated guts. Following these demonstrations, possible endogenous cellulase components were purified from several cellulose-digesting invertebrates, but this research did little to change the general view concerning animal cellulose digestion. Thanks to recent developments in molecular biology, the existence of cellulases of animal origin has been firmly established. To date, cellulase genes have been reported from arthropods (insects and a crayfish) and nematodes. This paper describes and discusses the presence and nature of endogenous cellulases in higher animals.

Hydrogen is the central free intermediate during lignocellulose degradation by termite gut symbionts

“…It consists mainly of cellulose and hemicelluloses, both of which are degraded with high efficiency during gut passage by the termite (65-99%, reviewed in Breznak and Brune, 1994). Although termites secrete their own cellulases and hemicellulases into foregut and midgut (Inoue et al, 1997;Watanabe and Tokuda, 2001;Tokuda et al, 2004Tokuda et al, , 2005, it is generally accepted that most of the polysaccharide degradation in lower termites occurs in the enlarged hindgut (Inoue et al, 1997;Tokuda et al, 2005), a bioreactorlike compartment with increased retention time and tightly packed with microorganisms (Breznak and Brune, 1994;Brune, 1998).…”

“…It consists mainly of cellulose and hemicelluloses, both of which are degraded with high efficiency during gut passage by the termite (65-99%, reviewed in Breznak and Brune, 1994). Although termites secrete their own cellulases and hemicellulases into foregut and midgut (Inoue et al, 1997;Watanabe and Tokuda, 2001;Tokuda et al, 2004Tokuda et al, , 2005, it is generally accepted that most of the polysaccharide degradation in lower termites occurs in the enlarged hindgut (Inoue et al, 1997;Tokuda et al, 2005), a bioreactorlike compartment with increased retention time and tightly packed with microorganisms (Breznak and Brune, 1994;Brune, 1998).In lower termites, the hindgut microbiota comprises flagellate protozoa, which are considered the primary agents of lignocellulose degradation, and a great variety of prokaryotes, whose particular function is often unknown (Breznak, 2000;Brune and Stingl, 2005;Brugerolle and Radek, 2006;Brune, 2006). About 70 years ago, Robert E Hungate was the first to realize that H 2 , CO 2 , and acetate are the main degradation products formed by the large cellulolytic protozoa (Hungate, 1939(Hungate, , 1943) that occupy the www.nature.com/ismej bulk of the hindgut volume of all lower termites (reviewed by Brune and Stingl, 2005).…”

Degradation of Plant-derived Carbohydrates in Wetlands

“…Widespread distribution of cellulase has been recognized in fungi, bacteria, plants, herbivorous invertebrates including insects and mollusks, and the enzyme origin had been assumed to be symbiotic microbes (Potts and Hewitt 1973;Marshall 1973;Pesis et al 1978;Tomme et al 1995;Watanabe and Tokuda 2001;Tsuji et al 2013;Rahman et al 2014). However, the discovery of an endogenous cellulase gene located in the host chromosome of an insect refuted the symbiotic theory (Watanabe et al 1998).…”

“…Cellulose, the most abundant organic substance on earth, is chemically stable and plays an important role in maintaining the physical strength of the cell walls of plants and phototrophic bacteria (Watanabe and Tokuda 2001). The physical strength of the cell wall is due to the primary structure of cellulose, which consists of monomeric chains of D-glucopyranose bound by b-1,4-glycoside linkages, resulting in the formation of cellulose microfibrils interconnected by hydrogen bonds (Watanabe and Tokuda 2010 ; Fig.…”

Expression of recombinant sea urchin cellulase SnEG54 using mammalian cell lines

“…1,4--glucosidase (EC 3.2.1.21) is required for complete de-polymerization of cellulose to glucose. These enzymes have been isolated from bacteria and fungi [1], plants [2], molds [3], microbes from animal intestines [4], and herbivorous invertebrates such as arthropods [5][6][7][8][9][10], nematodes [10], mollusks [11][12][13][14][15][16] and an echinoderm [17].…”