Invited Review: Adhesion Mechanisms of Rumen Cellulolytic Bacteria

Abstract

We divided the adhesion process of the predominant cellulolytic rumen bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus into four phases: 1) transport of the nonmotile bacteria to the substrate; 2) initial nonspecific adhesion of bacteria to unprotected sites of the substrate that is dominated by constitutive elements of bacterial glycocalyx; 3) specific adhesion via adhesins or ligands formation with the substrate, which can be dominated by several bacterial organelles including cellulosome complexes, fimbriae connections, glycosylated epitopes of cellulose-binding protein (CBP) or glycocalyx, and cellulose-binding domain (CBD) of enzymes; 4) proliferation of the attached bacteria on potentially digestible tissues of the substrate. Each of the phases and its significance in the adhesion process are described. Factors affecting bacterial adhesion are described including: 1) factors related to bacterial age, glycocalyx condition, and microbial competition; 2) factors related to the nature of substrate including, cuticle protection, surface area, hydration, and ionic charge; and 3) environmental factors including pH, temperature, and presence of cations and soluble carbohydrate. Based on the information available from the literature, it appears that each of the predominant rumen bacteria--F. succinogenes, R. flavefaciens, and R. albus--has a specific mechanism of adhesion to cellulose. In F. succinogenes, both the glycosidic residues of the outer membrane CBP and especially of the 180-kDa CBP, and the distinct CBD of EG2 EGF and Cl-stimulated cellobiosidase, may play a role in the adhesion to cellulose. No direct evidence, except scanning electron microscopy observations, yet supports the existence of either cellulosome complex or fimbriae structures involved in the adhesion mechanism of F. succinogenes. At least two mechanisms, cellulosome-like complexes and carbohydrate epitopes of the glycocalyx layer are involved in the specific adhesion of R. flavefaciens to cellulose. Ruminococcus albus possesses at least two mechanisms for specific adhesion to cellulose: a cellulosomal-like mechanism, and a CbpC (Pil)-protein mechanism that probably involves the production of fimbrial-like structures. Indirect and direct studies suggested that carbohydrate epitopes of CBPs and CBD epitope of cellulases may also be involved mostly in the nonspecific phase of adhesion of R. albus.

Design, implementation and interpretation of in vitro batch culture experiments to assess enteric methane mitigation in ruminants—a review

“…Fluid and particulate associated bacterial populations and methanogenic archaea (Shin et al, 2004) differ in growth characteristics and in the activities of most enzymes (Moharrery and Das, 2001). Microorganisms in rumen liquid (20 to 30% of total microbes) including free-living bacteria and bacteria detached from solid substrate, have little direct involvement in structural carbohydrate digestion (Miron et al, 2001). Microbes attached to feed particles predominate (70 to 80% of microbial matter and microbial ATP production) and play a key role in feed particle digestion in the rumen (Miron et al, 2001;Trabalza-Marinucci et al, 2006).…”

Relationship between chemical components, bacterial adherence and in vitro fermentation of tropical forage legumes

“…The adhesion process is affected by factors associated to bacteria cells, substrate type and rumen environment (MIRON; BEN-GHEDALLIA; MORRISON, 2001). In forages, the cutin present on particle surface, and the phenolic compounds (i.e.…”

Influence of an increase in diet structure on milk conjugated linoleic acid content of cows fed extruded linseed

“…Choi et al (2005) showed that the pH had a marked influence on the biohydrogenation by rumen bacteria. Adhesion of rumen cellulolytic bacteria to cellulose is a necessity for subsequent cellulose digestion and is reduced by even modest declines in pH, whereas, under neutral pH, cellulose digestion is optimal and the growth of cellulolytic bacteria is maximum (Miron et al, 2001;Mouriñ o et al, 2001;Choi et al, 2005). According to this mechanism, the likely higher pH with the 'SV 1.73' diet may have enhanced the adhesion of cellulolytic bacteria to cellulose, boosting cellulose digestion and, hence, the growth of cellulolytic bacteria.…”