ABSTRACT
Mitigating methane production by ruminants is a significant challenge to global livestock production. This research offers a new paradigm to reduce methane emissions from ruminants by breeding climate-clever clovers. We demonstrate wide genetic diversity for the trait methanogenic potential in Australia's key pasture legume, subterranean clover (Trifolium subterraneum L.). In a bi-parental population the broadsense heritability in methanogenic potential was moderate (H2 = 0.4) and allelic variation in a region of Chr 8 accounted for 7.8% of phenotypic variation. In a genome-wide association study we identified four loci controlling methanogenic potential assessed by an in vitro fermentation system. Significantly, the discovery of a single nucleotide polymorphism (SNP) on Chr 5 in a defined haplotype block with an upstream putative candidate gene from a plant peroxidase-like superfamily (TSub_g18548) and a downstream lectin receptor protein kinase (TSub_g18549) provides valuable candidates for an assay for this complex trait. In this way haplotype variation can be tracked to breed pastures with reduced methanogenic potential. Of the quantitative trait loci candidates, the DNA-damage-repair/toleration DRT100-like protein (TSub_g26967), linked to avoid the severity of DNA damage induced by secondary metabolites, is considered central to enteric methane production, as are disease resistance (TSub_g26971, TSub_g26972, and TSub_g18549) and ribonuclease proteins (TSub_g26974, TSub_g26975). These proteins are good pointers to elucidate the genetic basis of in vitro microbial fermentability and enteric methanogenic potential in subterranean clover. The genes identified allow the design of a suite of markers for marker-assisted selection to reduce rumen methane emission in selected pasture legumes. We demonstrate the feasibility of a plant breeding approach without compromising animal productivity to mitigate enteric methane emissions, which is one of the most significant challenges to global livestock production.
ABSTRACT
Methanogenic archaea (methanogens) are common inhabitants of the mammalian intestinal tract. In ruminants, they are responsible for producing abundant amounts of methane during digestion of food, but selected bioactive plants and compounds may inhibit this activity. Recently, we have identified that, Biserrula pelecinus L. (biserrula) is one such plant and the current study investigated the specific anti-methanogenic activity of the plant. Bioassay-guided extraction and fractionation, coupled with in vitro fermentation batch culture were used to select the most bioactive fractions of biserrula. The four fractions were then tested against five species of methanogens grown in pure culture. Fraction bioactivity was assessed by measuring methane production and amplification of the methanogen mcrA gene. Treatments that showed bioactivity were subcultured in fresh broth without the bioactive fraction to distinguish between static and cidal effects. All four fractions were active against pure cultures, but the F2 fraction was the most consistent inhibitor of both methane production and cell growth, affecting four species of methanogens and also producing equivocal-cidal effects on the methanogens. Other fractions had selective activity affecting only some methanogens, or reducing either methane production or methanogenic cell growth. In conclusion, the anti-methanogenic activity of biserrula can be linked to compounds contained in selected bioactive fractions, with the F2 fraction strongly affecting key rumen methanogens. Further study is required to identify the specific plant compounds in biserrula that are responsible for the anti-methanogenic activity. These findings will help devise novel strategies to control methanogen populations and activity in the rumen, and consequently contribute in reducing greenhouse gas emissions from ruminants.
