A new species concept for the clinically relevant Mucor circinelloides complex

Abstract

Mucor species are common soil fungi but also known as agents of human infections (mucormycosis) and used in food production and biotechnology. Mucor circinelloides is the Mucor species that is most frequently isolated from clinical sources. The taxonomy of Mucor circinelloides and its close relatives (Mucor circinelloides complex – MCC) is still based on morphology and mating behaviour. The aim of the present study was a revised taxonomy of the MCC using a polyphasic approach. Using a set of 100 strains molecular phylogenetic analysis of five markers (ITS, rpb1, tsr1, mcm7, and cfs, introduced here) were performed, combined with phenotypic studies, mating tests and the determination of the maximum growth temperatures. The multi-locus analyses revealed 16 phylogenetic species of which 14 showed distinct phenotypical traits and were recognised as discrete species. Five of these species are introduced as novel taxa: M. amethystinus sp. nov., M. atramentarius sp. nov., M. variicolumellatus sp. nov., M. pseudocircinelloides sp. nov., and M. pseudolusitanicus sp. nov. The former formae of M. circinelloides represent one or two separate species. In the MCC, the simple presence of well-shaped zygospores only indicates a close relation of both strains, but not necessarily conspecificity. Seven species of the MCC have been implemented in human infection: M. circinelloides, M. griseocyanus, M. janssenii, M. lusitanicus, M. ramosissimus, M. variicolumellatus, and M. velutinosus.

A Revised Species Concept for OpportunisticMucorSpecies Reveals Species-Specific Antifungal Susceptibility Profiles

“…The main results of our study are the species-specific AFS profiles of opportunistic Mucor species based on the revised taxonomy, which further support the recent taxonomic revision (6) (6), exhibited different AFS profiles. Mucor lusitanicus showed high MIC values for all azoles tested.…”

“…Molecular species identification based on internal transcribed spacer (ITS) sequences (see Table S1 in the supplemental material) was unambiguous for all strains studied. ITS sequences of strains that were not identified in former taxonomic studies (6,40) showed ITS sequence similarities of Ն99% with the respective ex-type strains.…”

“…In Table S1 in the supplemental material) were studied belonging to three different families: (1) Mucoraceae: (13), M. racemosus f. racemosus (4), M. ramosissimus (1), M. variicolumellatus (2), and M. velutinosus (7); (ii) Rhizopodaceae: Rhizopus arrhizus (6) and R. microsporus (6); and (iii) Lichtheimiaceae: Lichtheimia corymbifera (8), L. ramosa (2), and Rhizomucor pusillus (5). Strains originated from clinical or environmental sources (Table S1).…”

“…For mucoralean genera with recently updated taxonomy, such as Rhizopus and Lichtheimia (32)(33)(34), antifungal susceptibility profiles of the opportunistic members have been published (28,29,35). In Mucor, currently twelve species are known to cause infections in humans and animals (6), but comprehensive antifungal susceptibility (AFS) data only exist for M. circinelloides, M. indicus, and M. ramosissimus (23,28,31,36). Mucor circinelloides and its relatives were recently taxonomically revised resulting in the recognition of its classical formae as independent species (M. circinelloides sensu stricto, M. griseocynanus, M. janssenii, and M. lusitanicus), the acceptance of M. velutinosus as a discrete species (37,38), and the description of several new Mucor species (6).…”

“…Therefore, we studied the MICs of 101 strains of 18 species against six antifungals according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) protocol (39). We included Mucor species that have been reported to cause superficial as well as invasive infections on the basis of a molecular identification (4,6,37,38,40). We also studied Mucor amphibiorum that is only known to infect frogs, toads, and platypus (41) and Cokeromyces recurvatus because this species is related to Mucor (40) and has been isolated from clinical sources as well (42)(43)(44).…”