The family Nocardioidaceae

Abstract

Nocardioidaceae, a family within the order Propionibacteriales in the Propionibacterinae, embraces the genera Nocardioides, Marmoricola, Aeromicrobium, Kribbella, Actinopolymorpha, Thermasporomyces, and Flindersiella. Recent analysis of 16S rRNA gene sequences (using different clustering algorithms) shows that the genera which currently belong to the family Nocardioidaceae form at least two separate phylogenetic clusters. The two clusters are approximately at the same distance from each other and also from the family Propionibacteriaceae. The grouping is strengthened also by morphological and chemotaxonomic features. They are Gram-positive bacteria. Young cultures within the family show different morphologies, ranging from branching vegetative hyphae and pleomorph shapes to irregular rods and coccoid cells. Chemoorganotrophic organisms, having respiratory type of metabolism, are mostly catalase positive. Their cell-wall peptidoglycan contains LL-diaminopimelic acid and glycine as diagnostic amino acid (peptidoglycan A3γ). Their predominant menaquinone component is with partially saturated side chain, consisting 8, 9, or 10 isoprene units. Mycolic acids are absent. Members of the family occur in various environments (soils, aquatic environments, plants, etc.); no medically relevant strains or species have been described within the family till now. Some members of the family are active in degradation of recalcitrant chemicals. This contribution is a modified and updated version of previous family descriptions (Nesterenko et al. 1985, 1990; Stackebrandt et al. 1997; Zhi et al. 2009).