Cellulose, the most abundant structural component of plant
cell walls, is insoluble and extremely difficult to digest.
However, anaerobic microbes formed a large extracellular
enzyme complex called the cellulosome, which consists of a
scaffolding protein and many bound cellulases (Doi and
Kosugi 2004). In rumen, cellulolytic bacteria (R. flavefaciens,
R. albus, and F. succinogenes) predominately perform
the biodegradation of cellulose (Stevenson and Weimer
2007). Recently, new cellulose degrading species
Cellulosilyticum ruminicola has been reported from Yak
rumen (Cai et al. 2010). In anaerobic rumen fungi
Orpinomyces sp. strain PC-2, the enzymes that degrade
cellulose and hemicelluloses are also found associated with
cellulosomal and polycellulosomal complexes, where
enzymes are attached through fungal dockerins to scaffolding
proteins (Ljungdahl 2008). Piromyces sp. strain E2 has
also been reported to produce similar cellulosomes like
complexes (Steenbakkers et al. 2008). Recently, Joblin et
al. (2010) also suggested presence of cellulosomes in
Neocallimastix and Caecomyces.