The Nocardiaceae are a family of aerobic, non-fastidious, high G+C, Gram-positiveactinomycetes that are commonly found in soil and water.[3] Members of this family have been isolated from Antarctic soils.[4] Nocardiaceae present coccobacilli, filamentous or, rarely, fragmented and palisading forms,[5] and filamentous species grow in a branching morphological pattern similar to fungal hyphae.[6]
Genomics
The Nocardiaceae form a monophyletic clade within the Corynebacteriales in both 16S rRNA and protein-based phylogenetic trees.[7][8] A number of conserved signature indels and conserved signature proteins have been identified which are uniquely found in the genera Nocardia and Rhodococcus, supporting a close relationship between the two genera.[8] Recent proposals have been made, based on 16S rRNA signature nucleotides and chemotaxonomic markers, to add the genera Gordonia, Skermania, Williamsia, Millisia, and Smaragdicoccus to the family Nocardiaceae.[7][9] However, no conserved signature indels or proteins have been found that are commonly shared by Nocardia, Rhodococcus, and Gordonia, the fully sequenced members of the proposed Nocardiaceae revision.[8]
Pathogenic capacity
Some species colonize animals, and members of the Nocardia and Rhodococcus genera can cause infection in humans and livestock.[10] Nocardiosis represent also a serious health problem for fish (marine or not).[11] Many members of this family integrate mycolic acids into their cell wall, and as a result, Nocardia spp. may be mistaken for mycobacteria when viewed under a microscope following an acid-fast stain.[12]
Environmental effects
Wastewater foaming
Nocardia species are often responsible for the accumulation of foam that occurs in activated sludge during sewage treatment.[6][13][14][15] Biological foaming can be problematic for the water treatment process, and foam accumulation is reduced by adding surfactants to the wastewater.[16][17]
^ abBitton, G. Wastewater Microbiology. "Foam Microbiology." page 229.
^ abLudwig, W.; Euzéby, J.; Schumann, P.; Busse, H. J. R.; Trujillo, M. E.; Kämpfer, P.; Whitman, W. B. (2012). "Road map of the phylum Actinobacteria". Bergey's Manual® of Systematic Bacteriology. p. 1. doi:10.1007/978-0-387-68233-4_1. ISBN978-0-387-95043-3.
^Castellani, A. and A.J. Chalmers. 1919. Manual of Tropical Medicine, 3rd ed., Williams Wood and Co., New York, p. 1040.
^Austin , Brian and Dawn A. Austin. 2016. Aerobic Gram-Positive Rods and Cocci - Nocardiaceae Representatives in Bacterial fish pathogens, Springer International Publishing Switzerland, p.125-135