SPECIES DELIMITATION IN THE GENUS LIPOMYCES BY NUCLEAR GENOME COMPARISON

Species delimitation in Lipomyces was attempted by nuclear genome comp arison in conjuction with the re-evaluation of 48 physiological charac ters of 65 strains. High intraspecific (> 75%) and low interspecific ( < 28%) similarity values established that L. japonicus, L. lipofer and L. tetrasporus are genetically isolated, and also distinct from L. ko nonenkoae and L. starkeyi. Ambiguous similarity values were obtained w ith L. kononenkoae and L. starkeyi. Strains previously assigned to L. kononenkoae constitute two related clusters. While similarity values w ithin each cluster range from 76-99%, representatives of the two clust ers reassociate for only 47%. Since these clusters are differentiated by their ecologically relevant maximum growth temperature, L. kononenk oae is subdivided. Strains previously assigned to L. starkeyi resolve into four closely related clusters. While similarity values within eac h cluster range from 78-100%, representatives of the four clusters rea ssociate for only 59-69%. Since these four clusters are poorly differe ntiated, the subdivision of L. starkeyi does not appear possible witho ut recourse to other criteria. Four unassigned strains constitute a fu rther two clusters. Reassociation within these clusters is of the orde r of 91-100%, while reassociation between them occurs only at 59%. Rea ssociation of representatives of these clusters with those of the L. k ononenkoae and L. starkeyi complexes is around 40% and 31%, respective ly. These two clusters consequently appear to be intermediate between L. kononenkoae and L. starkeyi, and will, as such, have to be consider ed in any delimitation of these two species. A key to the taxa of Lipo myces and related genera of the Lipomycetaceae is given.