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Journal of Bacteriology, October 1999, p. 6488-6496, Vol. 181, No. 20
Department of Microbiology, Technical
University of Denmark, DK-2800 Lyngby, Denmark,1
and Department of Biochemistry, Comenius University, SK-842
15 Bratislava, Slovakia2
Received 25 May 1999/Accepted 11 August 1999
The genus Saccharomyces consists of several species
divided into the sensu stricto and the sensu lato groups. The genomes of these species differ in the number and organization of nuclear chromosomes and in the size and organization of mitochondrial DNA
(mtDNA). In the present experiments we examined whether these yeasts
can exchange DNA and thereby create novel combinations of genetic
material. Several putative haploid, heterothallic yeast strains were
isolated from different Saccharomyces species. All of these
strains secreted an a- or
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Horizontal Transfer of Genetic Material among
Saccharomyces Yeasts
kur1,*
-like pheromone recognized by S. cerevisiae tester strains. When interspecific crosses were performed by mass mating between these strains, hybrid zygotes were
often detected. In general, the less related the two parental species
were, the fewer hybrids they gave. For some crosses, viable hybrids
could be obtained by selection on minimal medium and their nuclear
chromosomes and mtDNA were examined. Often the frequency of viable
hybrids was very low. Sometimes putative hybrids could not be
propagated at all. In the case of sensu stricto yeasts, stable viable
hybrids were obtained. These contained both parental sets of
chromosomes but mtDNA from only one parent. In the case of sensu lato
hybrids, during genetic stabilization one set of the parental
chromosomes was partially or completely lost and the stable mtDNA
originated from the same parent as the majority of the nuclear
chromosomes. Apparently, the interspecific hybrid genome was
genetically more or less stable when the genetic material originated
from phylogenetically relatively closely related parents; both sets of
nuclear genetic material could be transmitted and preserved in the
progeny. In the case of more distantly related parents, only one
parental set, and perhaps some fragments of the other one, could be
found in genetically stabilized hybrid lines. The results obtained
indicate that Saccharomyces yeasts have a potential to
exchange genetic material. If Saccharomyces isolates could
mate freely in nature, horizontal transfer of genetic material could
have occurred during the evolution of modern yeast species.
*
Corresponding author. Mailing address: Department of
Microbiology, Technical University of Denmark, Building 301, DK-2800 Lyngby, Denmark. Phone: (45) 45 252518. Fax: (45) 45 932809. E-mail: imjp{at}pop.dtu.dk.
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