This study describes the isolation and characterization of Peptococcus heliotrinreducans, a novel obligately anaerobic, Gram-positive coccus from sheep rumen contents. The organism's most distinctive feature is its ability to perform reductive cleavage of hepatotoxic pyrrolizidine alkaloids (such as heliotrine) using hydrogen gas or formate as electron donors. Beyond pyrrolizidines, the bacterium can reduce nitrate and fumarate using the same hydrogen donors, deriving energy for growth from these reactions. The organism does not ferment carbohydrates but grows on enzymic hydrolysates of casein and yeast extract. It also utilizes arginine for energy production. Nine strains were isolated from different sheep, and an identical organism was recovered from cattle. Cell extracts contained a c-type cytochrome, consistent with involvement in electron transport. The organism is non-pathogenic and non-toxic. Detailed characterization confirmed its placement within the genus Peptococcus, distinguishing it from currently recognized species by its non-carbohydrate-fermenting metabolism, nitrate reduction, and DNA G+C content of approximately 36 mol%. The authors developed reliable isolation procedures using enrichment cultures with heliotrine and hydrogen-carbon dioxide gas mixtures.

Key findings

• Peptococcus heliotrinreducans is a novel strict anaerobe capable of reductive cleavage of hepatotoxic pyrrolizidine alkaloids using hydrogen or formate as electron donors
• The organism can use multiple hydrogen acceptors (pyrrolizidines, nitrate, fumarate) to oxidize formate and hydrogen, generating energy for growth
• The bacterium contains a c-type cytochrome and does not ferment carbohydrates, distinguishing it from other Peptococcus species
• The organism was successfully isolated from sheep rumen contents using enrichment culture with heliotrine and hydrogen-CO2 atmosphere, with limited success in cattle
• Nine strains were characterized with DNA G+C content of 35.4-36.9 mol%, and arginine dissimilation provides additional growth stimulation