Biochemical and molecular analyses of plant cell wall degrading enzymes from the rumen bacterium Ruminococcus albus 8

Xylanase;lichenase;Ruminococcus;glycoside hydrolase

Iakiviak, Michael ; Cann ; Isaac K.

关键词: Xylanase;    lichenase;    Ruminococcus;    glycoside hydrolase;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42456/Michael_Iakiviak.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Ruminants rely on microorganisms inhabiting the rumen to digest plant matter for subsequent fermentation to provide the host with the majority of its energy demands. Ruminococcus albus 8 is a rumen bacterium that efficiently degrades and ferments plant cell wall polysaccharides, such as cellulose and hemicelluloses. Xylan, a hemicellulosic polymer of β-1,4 linked xylose monomers may be appended with arabinose, glucuronic acid, and acetyl residues. Several classes of enzymes attack the polysaccharide to release the constitutive monosaccharides. Lichenin is a linear polymer of glucose linked together by β-1,3 and β-1,4 glycosidic bonds. Lichenin can be found in lichens and common feeds such as barley, sorghum, and wheat. A bioinformatic analysis of the genome of R. albus 8 revealed five genes encoding glycoside hydrolases predicted to hydrolyze the xylose backbone and several genes encoding putative accessory enzymes that are expected to remove side chains from xylans. The genes were cloned, heterologously expressed in E. coli, and biochemically characterized to determine how the enzymes function synergistically to release soluble sugars that can be fermented by R. albus 8. In an experiment designed to identify cellulase encoding genes in the genome of R. albus 8, four genes encoding lichenin degrading enzymes were identified. An enzyme mixture was created, and the components were shown to act synergistically to release, from the polysaccharide, cellobiose and cellotriose which are preferentially utilized by R. albus.