Phloroglucinol Degradation in the Rumen Promotes the Capture of Excess Hydrogen Generated from Methanogenesis Inhibition

Abstract

Strategies to manage metabolic hydrogen ([H]) in the rumen should be considered when reducing ruminant methane (CH4) emissions. However, little is known about the use of dietary treatments to stimulate rumen microorganisms capable of capturing the [H] available when CH4 is inhibited in vivo. The effects of the phenolic compound phloroglucinol on CH4 production, [H] flows and subsequent responses in rumen fermentation and microbial community composition when methanogenesis is inhibited were investigated in cattle. Eight rumen fistulated Brahman steers were randomly allocated in two groups receiving chloroform as an antimethanogenic compound for 21 days. Following that period one group received chloroform + phloroglucinol for another 16 days, whilst the other group received only chloroform during the same period. The chloroform treatment resulted in a decrease in CH4 production and an increase in H2 expelled with a shift in rumen fermentation toward higher levels of propionate and formate and lower levels of acetate at day 21 of treatment. Bacterial operational taxonomic units (OTUs) assigned to Prevotella were promoted whilst Archaea and Synergistetes OTUs were decreased with the chloroform treatment as expected. The shift toward formate coincided with increases in Ruminococcus flavefaciens, Butyrivibrio fibrisolvens, and Methanobrevibacter ruminantium species. The addition of chloroform + phloroglucinol in the rumen resulted in a decrease of H2 expelled (g) per kg of DMI and moles of H2 expelled per mol of CH4 decreased compared with the chloroform only treated animals. A shift toward acetate and a decrease in formate were observed for the chloroform + phloroglucinol-treated animals at day 37. These changes in the rumen fermentation profile were accompanied by a relative increase of OTUs assigned to Coprococcus spp., which could suggest this genus is a significant contributor to the metabolism of this phenolic compound in the rumen. This study demonstrates for the first time in vivo that under methanogenesis inhibition, H2 gas accumulation can be decreased by redirecting [H] toward alternative sinks through the nutritional stimulation of specific microbial groups. This results in the generation of metabolites of value for the host while also helping to maintain a low H2 partial pressure in the methane-inhibited rumen.

Effects of Phloroglucinol on In Vitro Methanogenesis, Rumen Fermentation, and Microbial Population Density

“…Increasing genus Coprococcus relative quantity might partly related to reduction of methane production as it increases the competition for [H] utilization with methanogen. This finding was in agreement with the study of Martinez-Fernandez et al (2017). An increase of acetate production was observed simultaneously with an increase of several operational taxonomic units (OTUs) assigned to Coprococcus spp.…”

“…Previous in vivo study showed that phloroglucinol can redirect [H] toward acetate when methanogenesis is completely inhibited by addition of chloroform (Martinez-Fernandez et al, 2017). This showed that in the absence of methanogenesis which is a natural [H] sink and H 2 pressure was high, phloroglucinol was able to redirect [H] toward acetate production.…”

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions

“…In contrast, butyrate precursors did not decrease H 2 accumulation caused by three inhibitors of methanogenesis in batch cultures . Martinez-Fernandez et al (2017) successfully used phlorglucinol as an e − acceptor to decrease the accumulation of H 2 and formate in the rumen of steers whose methanogenesis was inhibited with chloroform. An increase in acetate concentration observed when phlorglucinol was supplemented agrees with previous studies which had shown that phlorglucinol was reduced to acetate by rumen microorganisms using H 2 or formate as e − donors (Martinez-Fernandez et al, 2017).…”

“…Martinez-Fernandez et al (2017) successfully used phlorglucinol as an e − acceptor to decrease the accumulation of H 2 and formate in the rumen of steers whose methanogenesis was inhibited with chloroform. An increase in acetate concentration observed when phlorglucinol was supplemented agrees with previous studies which had shown that phlorglucinol was reduced to acetate by rumen microorganisms using H 2 or formate as e − donors (Martinez-Fernandez et al, 2017). Microbial additives can help removing constraints to the incorporation of [H] into pathways alternative to methanogenesis whose rate is enzyme-limited.…”

Review: The application of omics to rumen microbiota function

“…Microbial profiling studies using high throughput sequencing have been performed on the major ruminants investigating changes due to diet, subacute acidosis, methane emissions, feed efficiency, variation along the digestive tract, maternal influence and seasonal changes (Fouts et al, 2012;Lee et al, 2012;Li et al, 2012;Jami et al, 2014;Denman et al, 2015;Mao et al, 2015;Myer et al, 2015;Huws et al, 2016;Martinez-Fernandez et al, 2016;Abecia et al, 2017;Danielsson et al, 2017;Noel et al, 2017;Tapio et al, 2017b;Wetzels et al, 2017;Petri et al, 2018). But the most comprehensive study performed on ruminates to identify the core microbiota and define what variance in the rumen microbiome was attributed to ruminant species, diet and geographical location was undertaken by the rumen microbial census collaboration (Henderson et al, 2015).…”