Ecological characterization of three different phylogenetic groups belonging to the cellulolytic bacterial species Fibrobacter succinogenes in the rumen

Use of Asian selected agricultural byproducts to modulate rumen microbes and fermentation

In the last five decades, attempts have been made to improve rumen fermentation and host animal nutrition through modulation of rumen microbiota. The goals have been decreasing methane production, partially inhibiting protein degradation to avoid excess release of ammonia, and activation of fiber digestion. The main approach has been the use of dietary supplements. Since growth-promoting antibiotics were banned in European countries in 2006, safer alternatives including plant-derived materials have been explored. Plant oils, their component fatty acids, plant secondary metabolites and other compounds have been studied, and many originate or are abundantly available in Asia as agricultural byproducts. In this review, the potency of selected byproducts in inhibition of methane production and protein degradation, and in stimulation of fiber degradation was described in relation to their modes of action. In particular, cashew and ginkgo byproducts containing alkylphenols to mitigate methane emission and bean husks as a source of functional fiber to boost the number of fiber-degrading bacteria were highlighted. Other byproducts influencing rumen microbiota and fermentation profile were also described. Future application of these feed and additive candidates is very dependent on a sufficient, cost-effective supply and optimal usage in feeding practice.

Comparative studies of the composition of bacterial microbiota associated with the ruminal content, ruminal epithelium and in the faeces of lactating dairy cows

The objective of this research was to compare the composition of bacterial microbiota associated with the ruminal content (RC), ruminal epithelium (RE) and faeces of Holstein dairy cows. The RC, RE and faecal samples were collected from six Holstein dairy cows when the animals were slaughtered. Community compositions of bacterial 16S rRNA genes from RC, RE and faeces were determined using a MiSeq sequencing platform with bacterial‐targeting universal primers 338F and 806R. UniFrac analysis revealed that the bacterial communities of RC, RE and faeces were clearly separated from each other. Statistically significant dissimilarities were observed between RC and faeces (P = 0.002), between RC and RE (P = 0.003), and between RE and faeces (P = 0.001). A assignment of sequences to taxa showed that the abundance of the predominant phyla Bacteroidetes was lower in RE than in RC, while a significant higher (P < 0.01) abundance of Proteobacteria was present in RE than in RC. When compared with the RC, the abundance of Firmicutes and Verrucomicrobia was higher in faeces, and RC contained a greater abundance of Bacteroidetes and Tenericutes. A higher proportions of Butyrivibrio and Campylobacter dominated RE as compared to RC. The faecal microbiota was less diverse than RC and dominated by genera Turicibacter and Clostridium. In general, these findings clearly demonstrated the striking compositional differences among RC, RE and faeces, indicating that bacterial communities are specific and adapted to the harbouring environment.

Bean husks as a supplemental fiber for ruminants: potential use for activation of fibrolytic rumen bacteria to improve main forage digestion

This study evaluated the suitability of easily digested fiber sources as a supplemental fiber to improve overall fiber digestion in ruminants. First, the degradation of five fibrous feedstuffs and the stimulatory effects on rumen bacteria were examined in situ. Chickpea and lablab bean husks were selected for their potential use due to their large degradable fraction (>94%), which had a stimulatory effect on fibrolytic rumen bacteria such as Fibrobacter succinogenes. Second, a possible improvement in the digestibility of rice straw diet by husk supplementation was monitored in vivo. Four dietary treatments comprising RS (rice straw and concentrate), CHM (RS supplemented with Myanmar chickpea husk), CHE (RS with Egyptian chickpea husk) and LH (RS with lablab bean husk) were allocated to four wethers. The digestibility of acid detergent fiber was 3.1-5.5% greater in CHM and LH than RS. Total volatile fatty acid concentration was higher in LH than other treatments. Acetate proportion was higher in LH than RS. Ruminal abundance of F. succinogenes was 1.3-1.5 times greater in CHM and LH than RS. These results suggest that bean husk supplementation, especially lablab bean husk, might improve the nutritive value of rice straw diet by stimulating fibrolytic bacteria.

Fibrolytic capabilities of ruminal bacterium Fibrobacter succinogenes in relation to its phylogenetic grouping

To characterize the fibrolytic function of Fibrobacter succinogenes strains in relation to their phylogenetic grouping, 32 strains were newly isolated from the rumen of sheep. All new strains were classified into phylogenetic groups 1 or 2 including a novel subgroup of group 2. Importantly, the majority of the strains belonging to group 1 were isolated from ruminally incubated hay. Although almost complete degradation of Avicel was observed among all strains, significantly lower digestibility of three different forages was recorded for strain HM2 of group 3 than for the strains of groups 1 and 2. In a comparison of all strains, two group 1 strains showed significantly higher digestibility of alfalfa and orchard grass hays, while two strains of the novel subgroup of group 2 had lower digestibility of orchard grass hay. Adhesion ability of each strain did not necessarily associate with the extent of digestibility. Maximum growth on Avicel was higher in group 1 than in group 2 strains, and two group 1 strains showed a shorter lag time. The results suggest that the ecological prominence of group 1 is due to a mixture of strains that are diverse in their fibrolytic capability making this group highly adaptable to any forage.

Ecological and physiological characterization shows that Fibrobacter succinogenes is important in rumen fiber digestion - review

Fibrobacter succinogenes is a major cellulolytic species in the rumen. On the basis of molecular data, this species can be classified into four phylogenetic groups. Recently gathered ecological and physiological data have revealed the importance of this species, particularly phylogenetic group 1, in rumen fiber digestion. These data indicate that group 1 should be the focus of future efforts to maximize the fibrolytic function of the rumen.