Microbes Mix it Up: Prokaryote-Eukaryote Promiscuity Shuffles the Gene Pool

The July 2005 ASM News , Vol. 71, No. 7 reports:

(Hall C, Brachat S, Dietrich FS. 2005. Contribution of horizontal gene transfer to the evolution of Saccharomyces cerevisiae . Eukaryotic Cell 4:1102-1115.)

Just two widely accepted examples of prokaryote-to-eukaryote horizontal gene transfer (HGT) are known- “special cases” -and its occurrence is still a matter of debate.   Now, Charles Hall of Fred S. Dietrich's lab at Duke University Medical Center, Durham, NC, and others have identified 10 potential cases of horizontal gene transfer in Saccharomyces cerevisiae .   One, encoding the enzyme dihydroorotate dehydrogenase (DHOD), appears to have entered the Saccharomycetaceae from the Lactobacillales , after the divergence of the S. cerevisiae evolved from genes present in the ancestral yeasts more than 100 million years ago,” says Hall.   The small number that have been incorporated into the yeast genome since then have resulted in novel traits.   “Our work shows that HGT is important in the evolution of single-celled eukaryotes,” says Hall.   Thus, “it's part of the evolutionary toolkit of all microbes.”

According to Joseph Heitman, Faculty of 1000 Biology member and James B. Duke professor in the Department of Molecular Genetics and Microbiology at the Duke University Medical Center:

“This study reports unequivocal evidence that several genes have been horizontally transferred from bacteria into the genome of the eukaryotic ascomycetous yeast Saccharomyces cerevisiae, representing one of only a few documented cases of transkingdom DNA delivery that have occurred during evolution. While horizontal gene transfer is rampant in bacteria, it has been much more difficult to establish whether this process has contributed to shaping fungal genomes. In this study, the now complete genomes for S. cerevisiae and the filamentous ascomycete Ashbya gossypii were compared, revealing candidate horizontally acquired genes in each lineage. Hall and Dietrich go on to document carefully that the URA1 gene encoding the enzyme dihydroorotate dehydrogenase (DHOD) and the BDS1 gene encoding an aryl and alkyl sulfatase were acquired from bacteria by yeast. The acquisition of both genes conferred novel phenotypic plasticity upon the recipient yeast, likely providing sufficient selective pressure to ensure their retention in the genome. These studies establish unequivocally that horizontal gene transfer has occurred in the fungal kingdom, opening the door to a broader analysis in other phyla and experimental studies on the mechanism and environmental niches in which bacteria and fungi might exchange genetic material.”