# Examining homoacetogens in feces from adult and juvenile kangaroos with the aim of finding competitive strains to hydrogenotrophic methanogens

## TL;DR

This study explores bacteria in kangaroo feces that can convert hydrogen and carbon dioxide into acetic acid instead of methane, potentially offering a way to reduce methane emissions.

## Contribution

The study identifies and characterizes fast-growing homoacetogenic bacteria from juvenile kangaroos that could replace methane-producing microbes in ruminants.

## Key findings

- Juvenile kangaroo feces produced acetic acid but no methane when cultured.
- Over 70% of gene copies in the culture belonged to Clostridia, with Paraclostridium and Blautia as dominant genera.
- The culture included Actinomyces spp., a newly identified homoacetogenic genus in macropod GI tracts.

## Abstract

We examined the microbial populations present in fecal samples of macropods capable of utilizing a mixture of hydrogen and carbon dioxide (70:30) percent. The feces samples were cultured under anaerobic conditions, and production of methane or acetic acids characteristic for methanogenesis and homoacetogenesis was measured. While the feces of adult macropods mainly produced methane from the substrate, the sample from a 2-month-old juvenile kangaroo only produced acetic acid and no methane. The stable highly enriched culture of the joey kangaroo was sequenced to examine the V3 and V4 regions of the 16S rRNA gene. The results showed that over 70% of gene copies belonged to the Clostridia class, with Paraclostridium and Blautia as the most predominant genera. The culture further showed the presence of Actinomyces spp., a genus which has only been identified in the GI tract of macropods in a few studies, and where none, to our knowledge, have been classified as homoacetogenic. The joey kangaroo mixed culture showed a doubling time of 3.54 h and a specific growth rate of 0.199/h, faster than what has been observed for homoacetogenic bacteria in general.

Enteric methane emissions from cattle are a significant contributor to greenhouse gas emissions worldwide. Methane emissions not only contribute to climate change but also represent a loss of energy from the animal's diet. However, methanogens play an important role as hydrogen sink to rumen systems; without it, the performance of hydrolytic organisms diminishes. Therefore, effective strategies of methanogen inhibition would be enhanced in conjunction with the addition of alternative hydrogen sinks to the rumen. The significance of our research is to identify homoacetogens present in the GI tract of kangaroos and to present their performance in vitro, demonstrating their capability to serve as alternatives to rumen methanogens.