Genetic Relatedness of Marine Kluyveromyces Species

— The genetic relatedness of 22 strains of Kluyveromyces aestuarii, K. nonfermentans, and K. siamensis isolated from marine habitats in North and South America (United States, Brazil), East Asia (China, Taiwan, Japan, Thailand), and Australia was studied using molecular karyotyping, RAPD-PCR, phylogenetic analysis, and genetic hybridization analysis. The deep-sea species K. nonfermentans formed sterile hybrids with K. aestuarii and K. siamensis, had a unique karyotypic profile, and differed significantly in the nucleotide sequences of the 5.8S-ITS rDNA region and two nuclear genes (ACT1 and EF-1α). The phylogenetically more closely related species K. siamensis and K. aestuarii possessed similar molecular karyotypes, were partially genetically isolated (ascospore viability of 9–19%), and are apparently still in the process of divergence. K. aestuarii was shown to consist of two geographic populations that exhibited genome divergence at the level of taxonomic varieties.