Corynebacterium

Corynebacterium (kɔːˈraɪnəbækˌtɪəriəm,_-ˈrɪn-) is a genus of Gram-positive bacteria and most are aerobic. They are bacilli (rod-shaped), and in some phases of life they are, more specifically, club-shaped, which inspired the genus name (coryneform means "club-shaped"). They are widely distributed in nature in the microbiota of animals (including the human microbiota) and are mostly innocuous, most commonly existing in commensal relationships with their hosts. Some, such as C. glutamicum, are commercially and industrially useful. Others can cause human disease, including, most notably, diphtheria, which is caused by C. diphtheriae. As with various species of microbiota (including their relatives in the genera Arcanobacterium and Trueperella), they usually are not pathogenic, but can occasionally opportunistically capitalize on atypical access to tissues (via wounds) or weakened host defenses. The genus Corynebacterium was created by Lehmann and Neumann in 1896 as a taxonomic group to contain the bacterial rods responsible for causing diphtheria. The genus was defined based on morphological characteristics. Based on studies of 16S-rRNA, they have been grouped into the subdivision of Gram-positive Eubacteria with high G:C content, with close phylogenetic relationship to Arthrobacter, Mycobacterium, Nocardia, and Streptomyces. The term comes from Greek κορύνη, korýnē 'club, mace, staff, knobby plant bud or shoot' and βακτήριον, baktḗrion 'little rod'. The term "diphtheroids" is used to represent corynebacteria that are nonpathogenic; for example, C. diphtheriae would be excluded. The term diphtheroid comes from Greek διφθέρα, diphthérā 'prepared hide, leather'. Comparative analysis of corynebacterial genomes has led to the identification of several conserved signature indels (CSIs) that are unique to the genus. Two examples of CSIs are a two-amino-acid insertion in a conserved region of the enzyme phosphoribose diphosphate:decaprenyl-phosphate phosphoribosyltransferase and a three-amino-acid insertion in acetate kinase, both of which are found only in Corynebacterium species.