Isolation and attempted introduction of sugar alcohol‐utilizing bacteria in the sheep rumen

Abstract

Bacteria that use sorbitol, xylitol, maltitol and dulcitol (galactitol) were isolated from the sheep rumen following enrichments in which bacteria were grown in rumen fluid medium where the sugar alcohol was the only added energy source. Only isolates obtained with sorbitol and maltitol grew sufficiently rapidly to be considered for enrichment by the sugar alcohol in vivo. Isolate SS2, a strain of Selenomonas ruminantium var. lactilytica which grew on sorbitol at 0.87 h-1, was selected for further study and a rifampicin-resistant mutant, SS2/R5, was isolated to facilitate tracking in the mixed population. Despite an initial transient increase in numbers, a significant population of S. ruminantium SS2/R5 failed to establish in sheep which were dosed twice daily with 10 g of sorbitol. Continuous infusion of sorbitol increased numbers only slightly compared with twice-daily dosing. In vitro experiments indicated that strain SS2/R5 grew less well in the presence of other rumen organisms, particularly ciliate protozoa, than in pure culture. Furthermore, the concentration of sorbitol in vivo was lower than predicted from in vitro experiments, indicating that sorbitol was absorbed rapidly from the rumen. Similar observations were made with xylitol, dulcitol and maltitol. Proposed enrichment strategies that use sugar alcohols or other materials to support the growth of introduced bacteria will thus have to take account of the combined problems of microbe-microbe interactions and the loss of the compounds by absorption from the rumen.

Review: The compositional variation of the rumen microbiome and its effect on host performance and methane emission

“…Although these features serve as an anchor for studying the effect of different microbial makeups on the host over time (Li et al, 2009;Jewell et al, 2015), they also hinder the possibility of microbial manipulation and to follow the long-term effect of such changes. Most attempts at introducing bacteria, indigenous to the rumen, resulted in only a temporary The rumen microbiome and host physiology increase of the inoculum, followed by its decrease to extinction in a matter of days to a few weeks (Wallace and Walker, 1993;Krause et al, 2001a;Chiquette et al, 2008;Zebeli et al, 2012;Weimer et al, 2015). The microbiome is resilient to such an extent, that a recent study, which almost completely replaced the rumen fluid of one cow with the rumen fluid from another cow, showed that within just a few weeks, rumen microbiome content reverted to a content more closely resembling its original composition (Weimer et al, 2017).…”

Gut microbial adaptation to dietary consumption of fructose, artificial sweeteners and sugar alcohols: implications for host–microbe interactions contributing to obesity

“…was in fact reported as early as the 1930s (73). Sorbitol metabolism has also been observed by species of Selenomonas ruminantium in sheep rumen, suggesting this metabolic capacity may be widely distributed among microbes (74). Xylitol is generally regarded as beneficial in preventing oral lactobacilli, streptococci and actinomycetes growth; however, less is known about microbially mediated intestinal fermentation (75).…”

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

“…Several groups of workers have dosed fibrolytic bacteria into the rumen but have found that the inoculant usually disappears from the rumen [223–226]. One of the reasons given for this is that we do not yet understand how fibrolytic bacteria exist and reproduce at the fiber surface.…”