Commercial cultivation, industrial application, and potential halocarbon biosynthesis pathway of Asparagopsis sp.

The red macroalgal genus Asparagopsis consists of six identified species, which produce and store bromoform. In co-feed trials, the species A. taxiformis and A. armata inhibited enteric-generated methane (CH4 – a greenhouse gas) emissions in ruminants, owing to their bromoform content. Estimations suggest that global anthropogenic CH4 emissions could be reduced by up to 44%, which would significantly mitigate the greenhouse effect of CH4. Research showed that A. armata typically has an 8.5-fold higher bromoform content (average 1.45% of dry weight biomass (DWbiomass)) compared to A. taxiformis (0.17% DWbiomass). To date, however, only A. taxiformis can be cultivated in aquaculture indoor-controlled conditions (e.g. in southern Portugal and Hawaii, USA). Despite intensive studies, the synthesis pathway of bromoform in Asparagopsis has not yet been fully elucidated. Optimization of bromoform contents and biomass productivities for sustainable use in feed applications will require tank cultivation for A. armata under optimal environmental conditions and further studies are needed to fully understand the metabolic pathway of bromoform production. To lay the required foundation, this review briefly summarises the biological characteristics of Asparagopsis spp., putative halocarbon biosynthesis pathways and enzymes involved, the status of commercial cultivation, and the mechanism of inhibition of methane (CH4) formation in ruminants.