Unique aspects of fiber degradation by the ruminal ethanologen Ruminococcus albus 7 revealed by physiological and transcriptomic analysis

Abstract

BackgroundBacteria in the genus Ruminococcus are ubiquitous members of the mammalian gastrointestinal tract. In particular, they are important in ruminants where they digest a wide range of plant cell wall polysaccharides. For example, Ruminococcus albus 7 is a primary cellulose degrader that produces acetate usable by its bovine host. Moreover, it is one of the few organisms that ferments cellulose to form ethanol at mesophilic temperatures in vitro. The mechanism of cellulose degradation by R. albus 7 is not well-defined and is thought to involve pilin-like proteins, unique carbohydrate-binding domains, a glycocalyx, and cellulosomes. Here, we used a combination of comparative genomics, fermentation analyses, and transcriptomics to further clarify the cellulolytic and fermentative potential of R. albus 7.ResultsA comparison of the R. albus 7 genome sequence against the genome sequences of related bacteria that either encode or do not encode cellulosomes revealed that R. albus 7 does not encode for most canonical cellulosomal components. Fermentation analysis of R. albus 7 revealed the ability to produce ethanol and acetate on a wide range of fibrous substrates in vitro. Global transcriptomic analysis of R. albus 7 grown at identical dilution rates on cellulose and cellobiose in a chemostat showed that this bacterium, when growing on cellulose, utilizes a carbohydrate-degrading strategy that involves increased transcription of the rare carbohydrate-binding module (CBM) family 37 domain and the tryptophan biosynthetic operon.ConclusionsOur data suggest that R. albus 7 does not use canonical cellulosomal components to degrade cellulose, but rather up-regulates the expression of CBM37-containing enzymes and tryptophan biosynthesis. This study contributes to a revised model of carbohydrate degradation by this key member of the rumen ecosystem.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1066) contains supplementary material, which is available to authorized users.

Treatment of grain with organic acids at 2 different dietary phosphorus levels modulates ruminal microbial community structure and fermentation patterns in vitro

“…It is possible that LAc treatment stimulated propionate formation by offering an electron sink for H 2 , leading to enhancement of the succinate-propionate pathway and the synthesis of propionate (Nisbet et al, 2009). On the other hand, although acetate is known as a main fermentation product of cellulolytic bacterial species (Christopherson et al, 2014), propionate and butyrate are produced by many bacterial groups using lactate, resistant starch, pectins, and hemicelluloses as substrates (Marounek and Dušková, 1999;Brouns et al, 2002;Duncan et al, 2004). Treatment with organic acid enhances the content of resistant starch and the recovery of soluble fibers (Harder et al, 2015a,b), which serve as substrates for the formation of propionate and butyrate (Marounek and Dušková, 1999;Brouns et al, 2002;Duncan et al, 2004).…”

The severity of nonalcoholic fatty liver disease is associated with gut dysbiosis and shift in the metabolic function of the gut microbiota

“…There is little published information to guide hypotheses generation about this association. Ruminococcus are able to ferment complex carbohydrates, such as cellulose, pectine, resistant starch, and are acetate and propionate producers . The Ruminococcus genus is quite heterogeneous, including both beneficial and deleterious bacteria.…”

“…Ruminococcus are able to ferment complex carbohydrates, such as cellulose, pectine, resistant starch, (44,45) and are acetate and propionate producers. (46,47) The Ruminococcus genus is quite heterogeneous, including both beneficial and deleterious bacteria. For example, Ruminococcus bromii is known to have beneficial effects on health, (48) whereas other Ruminococcus species have been shown to be proinflammatory.…”

Microbial succession in the gastrointestinal tract of dairy cows from 2 weeks to first lactation

“…However, several calves also had low abundances of a Succinivibrio and a Ruminococcaceae OTU, which persisted in most adults. Both may be important in the adult fecal ecosystem as carbohydrate28 and fiber-degrading organisms2930, and their presence in some calves suggests that early acquisition of specific adult-associated microorganisms can occur.…”