Syntrophococcus sucromutans is a Gram-negative strictly anaerobic chemoorganotrophic Bacillota. These bacteria can be found forming small chains in the habitat where it was first isolated, the rumen of cows. It is the type strain of genus Syntrophococcus and it has an uncommon one-carbon metabolic pathway, forming acetate from formate as a product of sugar oxidation. Name and Discovery The genus name Syntrophococcus is combination of Greek terms: syn, meaning “together”, trophos, meaning “feeder”, and kokkos, meaning “berry”. The species name sucromutans is a combination of New Latin sucro, referring to any sugar, and Latin mutans, meaning “changing”. S. sucromutans was first isolated by Krumholz and Bryant from the rumen of a steer. They made a basal medium consisting of 5% rumen fluid and bicarbonate buffer incubated in 4:1 N2:CO2 conditions. The researchers were looking to find a bacterium that demethoxylated phenolic acids in the gut of ruminants, and this species was found to be the most prevalent prokaryote in the rumen to do such a process. Microbiology Phylogenetics and Genetics Because it is an anaerobic coccus that stains Gram negative, S. sucromutans was originally classified into the family Veillonellaceae. Further 16S rRNA gene analysis has shown that the species belongs in the family Lachnospiraceae in phylum Bacillota. S. sucromutans is the only member of its genus with Eubacterium cellulosolvens as its closest described relative. The type strain, ATCC 43584 or DSM 3224, has a G+C content of 52%. Growth S. sucromutans is a mesophile with a growth optimal temperature ranging from 35-42 °C and a growth range of 30-44 °C. The pH range for this Bacillota is close to neutral, 6.0-7.6, and will optimally grow in a slightly acidic environment, such as the rumen of a cow, at pH 6.4. Growth should be seen within 3 to 4 weeks if the above medium containing ruminal fluid is used. This complex medium provides it with all the nutrients necessary for optimal growth such as a mixture of vitamins, minerals, and trace metals. The main compounds that S. sucromutans must obtain from such ruminal fluid are phospholipids. It is even able to thrive without a ruminal fluid supplement if provided with phospholipids and fatty acids via a preparation such as 60% pure phosphatidylcholine. Morphology This species of coccus stains Gram-negative, is non-motile, cannot form spores, and forms short chains. Its size ranges from 1.0 to 1.3 μm in diameter. Pathogenicity Pathogenicity has