Characterisation of Four Species of the Genus Kluyveromyces by Mitochondrial DNA Restriction Analysis

In the present work, we determine the relationships at the within-species level among strains of Kluyveromyces dobzhanskii, K. lactis, K. marxianus, and K. thermotolerans, through the restriction analysis of their mtDNAs. The three first species showed a high level of intraspecific mtDNA divergence, this polymorphism is correlated to the varieties or species defined according to the original taxonomy of the genus, which is in concordance with that shown by other phenotypic or genotypic markers codified for by the nuclear genome. In these species, the analysis of the relationships among strains based on mtDNA restriction data agrees with previous classifications based on morphological traits and physiological abilities. On the contrary, K. thermotolerans showed a reduced level of intraspecific divergence compared to the other three, which indicates that this species either is a more recent species, has suffered a reduction of polymorphism due to the action of evolutionary forces, or presents a lower mtDNA substitution rate.