Diversity and delimitation of Rhizopus microsporus

Rhizopus microsporus has been used for centuries in the production of oriental fermented foods, but the species is also known as a toxin producer and from severe human infections. To study the diversity and species delimitation of Rhizopus microsporus, 48 isolates from the reference collection of the CBS-KNAW Fungal Biodiversity Centre, comprising nine environmental, ten clinical, and 23 foodborne strains, in addition to six strains from unknown sources and representing all existing varieties of the species, were examined. Sequence diversity was based on the internal transcribed spacer (ITS), and on a part of the actin (ACT) and translation elongation factor 1-alpha (TEF) genes. Differences in physiological properties were assessed including temperature relationships. Spore morphology was studied, mating type tests were performed, and MALDI-ToF profiles were generated. Clinical and food-associated strains as well as members of different varieties mated successfully and consequently they belong to a single biological species. Molecular differences did not match with any other parameter investigated. Based on these results the varieties of Rhizopus microsporus are reduced to synonyms.