TAXONOMY: Terrabacteria group -> Firmicutes -> Bacilli -> Bacillales -> Bacillales incertae sedis -> Bacillales Family XI. Incertae Sedis -> Gemella
'Gemella' is a genus of Gram-positive bacteria that thrive best at high partial pressure of CO2.Ovoid in shape and arranged in pairs, tetrads, small clusters, and sometimes in short chains. Cells stain Gram-positive, but some strains may decolorize readily and appear Gram-negative. Nonmotile and nonsporeforming. No growth at 10 or 45°C or in broth containing 6.5% NaCl. Negative bileesculin reaction. Facultatively anaerobic. Catalase- and oxidase-negative. Gas is not produced in MRS broth. Glucose and some other carbohydrates are fermented. Esculin, gelatin, and hippurate are not hydrolyzed. Pyrrolidonyl arylamidase is produced by most strains. Leucine aminopeptidase may or may not be produced. Nitrate is not reduced. Vancomycin-sensitive.They are facultatively anaerobic and give negative reactions to both oxidase and catalase tests. They are obligately fermentative, producing either a mixture of acetic and lactic acids or an equimolar molar mixture of acetic acid and CO2. For example, G. haemolysans ferments glucose forming a mixture of acetic and lactic acids in the absence of oxygen, whereas when oxygen is present, it forms acetic acid and CO2.[
DNA G + C content (mol%): 30–34.
Type species: Gemella haemolysans
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]