An infectious yeast has been found to reproduce through same-sex-type mating, according to a recent study by members of the Department of Molecular Microbiology and
Immunology.
The yeast, which causes certain blood stream infections , has the potential for same-sex reproduction, "what we previously thought was completely impossible," said Richard Bennett, assistant professor of biology, one of the lead researchers on the project.
The yeast, called Candida albicans, has two mating type cells, "a" and "alpha."
"It was assumed that, to undergo mating, an ‘a' cell had to mate with its partner, the ‘alpha,'" Bennett said. "What we show in this paper is that this is not actually the case. There are circumstances when the ‘a' cells will mate with ‘a' and ‘alpha' cells with ‘alpha.'"
Each mating type cell secretes pheromones that attract the partner type, driving reproduction, Bennett said. Both cell types have the potential to produce "a-" and "alpha-" pheromones, but an enzyme, Bar1, inactivates "alpha-" pheromones in "a" cells. Bennett and his research partners, Kevin Alby and Dana Schaefer, analyzed mutant cells in which this enzyme had been blocked. As a result, "a" cells were able to produce both types of pheromones and attract and reproduce with other "a" cells.
Bennett said the scientists were also able to observe this effect in wild-type cells in which Bar1 had not been blocked.
"If you have a mixture of wild-type ‘a' and ‘alpha' cells, ‘a's are producing lots of ‘a-' pheromones, and ‘alpha's are producing lots of ‘alpha-' pheromones," he said. "There's a big sea of pheromones."
Under these conditions, Bennett said, same mating-type reproduction results from the high concentration of pheromones.
This rare sort of natural same-sex-type matings was first observed in an unrelated study, Alby said, which led the researchers to examine the phenomenon further "out of curiosity."
"We saw an interesting phenotype and it didn't make sense," he said. "It was a completely fortuitous observation."
"Those are the things you go after," Bennett added. "You can't always chase the weird things that you see in the lab, but that's what we did."
While many news sources have reported the same-sex-type matings of C. albicans as proof of "homosexual yeast" or "gay yeast," Bennett said these headlines are inaccurate and prefers the term "homothallic" reproduction.
"People will think this has something to do with homosexuality in humans, and it doesn't," Bennett explained. "Because it's such a sensitive topic, the last thing I want to do is offend anyone or have anyone get the wrong impression when that's not what this story is about."
C. albicans is not the first species in which homothallic reproduction has been observed.Bennett said a fungus known as Cryptococcus neoformans can also undergo same-sex-type matings. The product of these matings in C. neoformans caused a recent outbreak of a fungal infection on Vancouver Island. Bennett said this outbreak proves the importance of research into homothallic reproduction.
"There's a potential for sex to go on in a population of cells where, previously, we had assumed that sex wasn't possible," he said. "The barriers to sexual reproduction might be a lot more fluid than we had previously thought."
