Abstract
The genus Turicella was proposed to harbor clinical strains isolated from middle-ear fluids of patients with otitis media. 16S rRNA phylogeny showed that it belonged to the mycolic acid-containing actinobacteria, currently classified in the order Corynebacteriales, and was closely related to the genus Corynebacterium. A new genus was proposed for the organisms as unlike corynebacteria they lacked mycolic acids and had different menaquinones. Here, we carried out large-scale comparative genomics on representative strains of the genera Corynebacterium and Turicella to check if this chemotaxonomic classification is justified. Three genes that are known to play an essential role in mycolic acid biosynthesis were absent in Turicella and two other mycolate-less Corynebacterium spp., explaining the lack of mycolic acids resulted from the deletion of genes and does not confer any phylogenetic context. Polyphasic phylogenetic analyses using 16S rRNA, bacterial core genes and genes responsible for synthesizing menaquinones unequivocally indicate that Turicella is a true member of the genus Corynebacterium. Here, we demonstrate that menaquinone and mycolic acid that have been used as critical taxonomic markers should be interpreted carefully, particularly when genome-based taxonomy is readily available. Based on the phylogenetic analysis, we propose to reclassify Turicella otitidis as Corynebacterium otitidis comb. nov.
Highlights
The order Corynebacteriales encompasses actinobacterial strains that are important in clinical, environmental and industrial microbiology (Lehmann and Neumann, 1896; Goodfellow and Jones, 2015)
A set of 93 genome sequences includes type strains of 77 Corynebacterium spp., one T. otitidis (Brinkrolf et al, 2012), and 14 representative genera classified in the order Corynebacteriales (Dietzia alimentaria, Gordonia bronchialis, Hoyosella altamirensis, Lawsonella clevelandensis, Millisia brevis, Mycobacterium tuberculosis, Nocardia asteroides, Rhodococcus rhodochrous, Segniliparus rotundus, Skermania piniformis, Smaragdicoccus niigatensis, Tomitella biformata, Tsukamurella paurometabola, and Williamsia muralis)
The application of chemotaxonomic procedures led to marked improvements in prokaryotic systematics (Goodfellow et al, 2012) though little attention was paid to the confidence that could be placed on chemical characters
Summary
The order Corynebacteriales encompasses actinobacterial strains that are important in clinical, environmental and industrial microbiology (Lehmann and Neumann, 1896; Goodfellow and Jones, 2015). The taxon is well defined by the presence of mycolic acids, a special type of long chain fatty acid only found in members of this order. The length and number of double bonds in mycolic acids are used as important chemotaxonomic markers for distinguishing between genera classified in the Corynebacteriales (Bernard et al, 2010; Marrakchi et al, 2014) though some species in the order lack mycolic acids (Funke et al, 1994; Collins et al, 1998; Wiertz et al, 2013). In some cases, a lack of congruence between these sets of data required the use of addition taxonomic evidence to clarify the situation
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