Identifying and exploring biohydrogenating rumen bacteria with emphasis on pathways including trans-10 intermediates.

BACKGROUND: Bacteria involved in ruminal formation of trans-10 intermediates are unclear. Therefore, this study aimed at identifying rumen bacteria that produce trans-10 intermediates from 18-carbon unsaturated fatty acids. RESULTS: Pure cultures of 28 rumen bacterial species were incubated individually in the presence of 40 µg/mL 18:3n-3, 18:2n-6 or trans-11 18:1 under control or lactate-enriched (200 mM Na lactate) conditions for 24 h. Of the 28 strains, Cutibacterium acnes (formerly Propionibacterium acnes) was the only bacterium found to produce trans-10 intermediates from 18:3n-3 and 18:2n-6, irrespective of the growth condition. To further assess the potential importance of this species in the trans-11 to trans-10 shift, different biomass ratios of Butyrivibrio fibrisolvens (as a trans-11 producer) and C. acnes were incubated in different growth media (control, low pH and 22:6n-3 enriched media) containing 40 µg/mL 18:2n-6. Under control conditions, a trans-10 shift, defined in the current study as trans-10/trans-11 ≥ 0.9, occurred when the biomass of C. acnes represented between 90 and 98% of the inoculum. A low pH or addition of 22:6n-3 inhibited cis-9, trans-11 CLA and trans-10, cis-12 CLA formation by B. fibrisolvens and C. acnes, respectively, whereby C. acnes seemed to be more tolerant. This resulted in a decreased biomass of C. acnes required at inoculation to induce a trans-10 shift to 50% (low pH) and 90% (22:6n-3 addition). CONCLUSIONS: Among the bacterial species studied,C. acnes was the only bacterium that have the metabolic ability to produce trans-10 intermediates from 18:3n-3 and 18:2n-6. Nevertheless, this experiment revealed that it is unlikely that C. acnes is the only or predominant species involved in the trans-11 to trans-10 shift in vivo.

Sharpea azabuensis: a ruminal bacterium that produces trans-11 intermediates from linoleic and linolenic acid.

To investigate the metabolism of 18:2n-6 and 18:3n-3 by pure cultures of Sharpea azabuensis, two different strains (RL 1 and ST18) were each incubated in the presence of 40 µg ml-1 18:2n-6 or 18:3n-3. Pure cultures of Butyrivibriofibrisolvens D1 and Butyrivibrio proteoclasticus P18 were included as control treatments. Similar to the metabolism of B. fibrisolvens, both S. azabuensis strains converted 18:2n-6 or 18:3n-3 to cis-9, trans-11 CLA or cis-9, trans-11, cis-15 CLnA, after which it was further reduced to trans-11 18:1 or trans-11, cis-15 18:2, respectively. B. proteoclasticus additionally reduced trans-11 18:1 to 18:0. Trans-11, cis-15 18:2 was also further metabolized by B. proteoclasticus, although trans-11 18:1 did not accumulate, and only minor amounts of 18:0 were formed. The time frame of 18:2n-6 and 18:3n-3 biohydrogenation by S. azabuensis was comparable with B. fibrisolvens, indicating that S. azabuensis and B. fibrisolvens might be alternative biohydrogenators of 18:2n-6 and 18:3n-3 in the rumen.

Rumen Biohydrogenation and Microbial Community Changes Upon Early Life Supplementation of 22:6n-3 Enriched Microalgae to Goats.

Dietary supplementation of docosahexaenoic acid (DHA)-enriched products inhibits the final step of biohydrogenation in the adult rumen, resulting in the accumulation of 18:1 isomers, particularly of trans(t)-11 18:1. Occasionally, a shift toward the formation of t10 intermediates at the expense of t11 intermediates can be triggered. However, whether similar impact would occur when supplementing DHA-enriched products during pregnancy or early life remains unknown. Therefore, the current in vivo study aimed to investigate the effect of a nutritional intervention with DHA in the early life of goat kids on rumen biohydrogenation and microbial community. Delivery of DHA was achieved by supplementing DHA-enriched microalgae (DHA Gold) either to the maternal diet during pregnancy (prenatal) or to the diet of the young offspring (postnatal). At the age of 12 weeks, rumen fluid was sampled for analysis of long-chain fatty acids and microbial community based on bacterial 16S rRNA amplicon sequencing. Postnatal supplementation with DHA-enriched microalgae inhibited the final biohydrogenation step, as observed in adult animals. This resulted particularly in increased ruminal proportions of t11 18:1 rather than a shift to t10 intermediates, suggesting that both young and adult goats might be less prone to dietary induced shifts toward the formation of t10 intermediates, in comparison with cows. Although Butyrivibrio species have been identified as the most important biohydrogenating bacteria, this genus was more abundant when complete biohydrogenation, i.e. 18:0 formation, was inhibited. Blautia abundance was positively correlated with 18:0 accumulation, whereas Lactobacillus spp. Dialister spp. and Bifidobacterium spp. were more abundant in situations with greater t10 accumulation. Extensive comparisons made between current results and literature data indicate that current associations between biohydrogenation intermediates and rumen bacteria in young goats align with former observations in adult ruminants.