Outer membrane vesicles from Fibrobacter succinogenes S85 contain an array of carbohydrate‐active enzymes with versatile polysaccharide‐degrading capacity

Abstract

Fibrobacter succinogenes is an anaerobic bacterium naturally colonising the rumen and cecum of herbivores where it utilizes an enigmatic mechanism to deconstruct cellulose into cellobiose and glucose, which serve as carbon sources for growth. Here, we illustrate that outer membrane vesicles (OMVs) released by F. succinogenes are enriched with carbohydrate-active enzymes and that intact OMVs were able to depolymerize a broad range of linear and branched hemicelluloses and pectin, despite the inability of F. succinogenes to utilize non-cellulosic (pentose) sugars for growth. We hypothesize that the degradative versatility of F. succinogenes OMVs is used to prime hydrolysis by destabilising the tight networks of polysaccharides intertwining cellulose in the plant cell wall, thus increasing accessibility of the target substrate for the host cell. This is supported by observations that OMV-pretreatment of the natural complex substrate switchgrass increased the catalytic efficiency of a commercial cellulose-degrading enzyme cocktail by 2.4-fold. We also show that the OMVs contain a putative multiprotein complex, including the fibro-slime protein previously found to be important in binding to crystalline cellulose. We hypothesize that this complex has a function in plant cell wall degradation, either by catalysing polysaccharide degradation itself, or by targeting the vesicles to plant biomass.

Microbial Diversity and Metabolic Potential in the Stratified Sansha Yongle Blue Hole in the South China Sea

“…The O 2 -deficient environments often display ecologically specialized microbial populations, potentially mediating organic carbon turnover and syntrophic interactions. In the bottom layer waters of the blue hole, the clades of syntrophic taxa identified could potentially degrade lignocellulosic plant material or algal-derived complex organic polymers in order to produce hydrogen (H 2 ), including Fibrobacter succinogenes (phylum Fibrobacteres) 60 , Latescibacteria 61 , and Firmicutes. The syntrophic bacteria also included taxa that convert small molecular compounds, such as glucose, pyruvic acid, short chain fatty acids, and glycerol to acetate and H 2 for CH 4 production-e.g., Thermotogae, Spirochaetae, Sebaldella termitidis (Fusobacteria), Elusimicrobium minutum (Elusimicrobia), Cloacimonetes, Atribacteria, Candidatus Acetothermus autotrophicum (Acetothermia), and Candidatus Hydrogenedentes 62 .…”

Fiber-associated spirochetes are major agents of hemicellulose degradation in the hindgut of wood-feeding higher termites

“…In view of the large proportion of putative cellulases (e.g., GH5_2, GH8, GH45) in the metatranscriptomic libraries (SI Appendix, Fig. S1 and Dataset S1), the low cellulase activity obtained with the particulate fraction might be explained by a less efficient recovery of the cellulases of Fibrobacteres and other fiber-associated microbiota, which are most probably localized in the glycocalyx (49) or outer membrane vesicles (50). Therefore, the astonishingly high cellulase activities in the soluble fraction of the hindgut paunch may be artificial (Fig.…”

A mechanistic overview of ruminal fibre digestion.

“…Several models of its cellulose degradation have been proposed, and some studies point towards cell attachment to cellulose using fibro-slime proteins and pili, bringing the substrate close to outer membrane-bound endo-cellulases (Burnet et al, 2015). The bacterium also produces outer-membrane vesicles (OMVs) containing carbohydrate-active enzymes, which are released from the cell to target plant biomass (Arntzen et al, 2017) (Fig. 4A).…”

“…The role of these OMVs in fibre-digestion is debated, with studies claiming their production is due aging of the cells (Gaudet and Gaillard, 1987). However, there is support they may have a biological role in cellulose degradation (Forsberg et al, 1981), with pre-treatment of switchgrass using the F. sugginogenes OMVs showing a 2.4-fold increase in subsequent saccharification by a commercial cellulase cocktail (Arntzen et al, 2017). It has been illustrated that other fibre-digesting Bacteroidetes species from the human gut also produce fibrolytic OMVs (Elhenawy et al, 2014) and it is hypothesized that F. sugginogenes OMVs could facilitate increased accessibility for the cell to the substrate by disrupting the complex structure of the lignocellulose (Arntzen et al, 2017).…”