Can freshwater plants and algae act as an effective feed supplement to reduce methane emissions from ruminant livestock?

Methane production by livestock is a substantial component of greenhouse gas emissions worldwide. The marine red algae, Asparagopsis taxiformis, has been identified as a possible supplement in livestock feeds due to its potent inhibition of methane production but currently is unable to be produced at scale. Finding additional taxa that inhibit methane production is therefore desirable. Here we provide foundational evidence of methanogenesis-inhibiting properties in Australian freshwater plants and algae, reviewing candidate species and testing species' chemical composition and efficacy in vitro. Candidate plant species and naturally-occurring algal mixes were collected and assessed for ability to reduce methane in batch testing and characterised for biochemical composition, lipids and fatty acids, minerals and DNA. We identified three algal mixes and one plant (Montia australasica) with potential to reduce methane yield in in vitro batch assay trials. All three algal mixes contained Spirogyra, although additional testing would be needed to confirm this alga was responsible for the observed activity. For the two samples that underwent multiple dose testing, Algal mix 1 (predominantly Spirogyra maxima) and M. australasica, there seems to be an optimum dose but sources, harvesting and storage conditions potentially determine their methanogenesis-inhibiting activity. Based on their compositions, fatty acids are likely to be acting to reduce methane in Algal mix 1 while M. australasica likely contains substantial amounts of the flavonoids apigenin and kaempferol, which are associated with methane reduction. Based on their mineral composition, the samples tested would be safe for livestock consumption at an inclusion rate of 20%. Thus, we identified multiple Australian species that have potential to be used as a feed supplement to reduce methane yield in livestock which may be suitable for individual farmers to grow and feed, reducing complexities of supply associated with marine alternatives and suggesting avenues for investigation for similar species elsewhere.

Transcriptomic and Histological Analysis of the Greentail Prawn (Metapenaeus bennettae) Following Light Crude Oil Exposure.

Oil spills pose a significant threat to marine biodiversity. Crude oil can partition into sediments where it may be persistent, placing benthic species such as decapods at particular risk of exposure. Transcriptomic and histological tools are often used to investigate the effects of hydrocarbon exposure on marine organisms following oil spill events, allowing for the identification of metabolic pathways impacted by oil exposure. However, there is limited information available for decapod crustaceans, many of which carry significant economic value. In the present study, we assess the sublethal impacts of crude oil exposure in the commercially important Australian greentail prawn (Metapenaeus bennettae) using transcriptomic and histological analyses. Prawns exposed to light, unweathered crude oil "spiked" sediments for 90 h were transferred to clean sediments for a further 72 h to assess recovery. Chemical analyses indicated that polycyclic aromatic hydrocarbons increased by approximately 65% and 91% in prawn muscle following 24 and 90 h of exposure, respectively, and significantly decreased during 24- and 72-h recovery periods. Transcriptomic responses followed an exposure and recovery pattern with innate immunity and nutrient metabolism transcripts significantly lowered in abundance after 24 h of exposure and were higher in abundance after 72 h of recovery. In addition, transcription/translation, cellular responses, and DNA repair pathways were significantly impacted after 24 h of exposure and recovered after 72 h of recovery. However, histological alterations such as tubule atrophy indicated an increase in severity after 24 and 72 h of recovery. The present study provides new insights into the sublethal impacts of crude oil exposure in greentail prawns and identifies molecular pathways altered by exposure. We expect these findings to inform future management associated with oil extraction activity and spills. Environ Toxicol Chem 2022;41:2162-2180. © 2022 John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

De Novo assembly and characterisation of the greentail prawn (Metapenaeus bennettae) hepatopancreas transcriptome - identification of stress response and detoxification transcripts.

Crude oil is a key contaminant in aquatic environments entering via natural and anthropogenic sources, causing toxicity in marine organisms. Traditionally, biomarkers have been utilised to determine crude oil exposure and effects in aquatic organisms, however advances in genomic technologies has led to increased adoption of transcriptomic approaches for identifying response and detoxification pathways following contaminant exposure. This study presents the first transcriptome for the greentail prawn (Metapenaeus bennettae), a commercially targeted benthic decapod crustacean from eastern and south-eastern Australia. The Trinity generated de novo assembly, after redundancy clustering, resulted in 86,401 contigs, of these 22,252 displayed strong homology to transcripts in the NCBI's non-redundant protein, Swiss-Prot and TrEMBL databases. Furthermore, Gene Ontology was assigned to 15,079 annotated contigs and KEGG Orthology was identified for 1318 annotated contigs. Transcripts encoding common biomarkers utilised to determine crude oil exposure were identified, including those for detoxification phase I and II enzymes; with 40 transcripts encoding for members of the cytochrome P450 gene family and 8 transcripts encoding glutathione S-Transferases (GSTs). Transcripts encoding oxidative stress enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and metallothionein (MT) were identified, as well as stress induced proteins including crustacean hyperglycemic hormone (CHH) and heat shock proteins (Hsps). The annotated transcriptome of the greentail prawn and the identification of detoxification and stress response transcripts, provides a necessary resource for future studies geared toward characterising differential transcriptomic patterns and molecular pathways after exposure to crude oil in this and other crustacean species of environmental and commercial importance.