In tough times, nasty fungus turns to sex

The fungi of the. Candida genus are. Known world-wide for. Their ability to cause serious infections. Were once. Thought to be asexual. Even after. Scientists discovered that the. Mating habits of Candida albicans were many. Varied, they. Remained convinced that many. Of the. More infectious ones didn't mate.

Now with. the. first. Report that Candida tropicalis can mate sexually, the. Chastity of the. whole. Genus comes. Into question.

“I think. the. really. Asexual fungi are. Going to turn out. To be the. Exception, rather than the. Rule,”. Says Richard Bennett, assistant professor of biology at. Brown University.

The revelation that C. tropicalis mates sexually isn't simply prurient. Some scientists hypothesize that the. Pathogen’s mix of sexual behaviours may. Have evolved as. A survival tactic.

When things. are. Going well, it. may. Be best. To reproduce asexually to keep a successful genome fairly stable. If conditions become hostile, then it. Makes sense to switch to sexual reproduction to accelerate the. Creation and proliferation of new, adaptive traits.

“Sex is really. Good for. Microbes when times are. Hard,”. Bennett says. “That’s the. Time when you. need. To adapt and try. various. Combinations of your. Genes or alleles.”

The at. Least occasional sexual nature of C. tropicalis may. Mean that the. Species can evolve faster. Than scientists thought it. Did, meaning it. may. Also be more capable of developing increased virulence or drug resistance.

Mysterious turn-on

The research began somewhat. Unintentionally in. the. Spring of 2010 when Allison M. Porman, a new. Graduate student, was on. A through. Bennett’s lab. Porman happened to notice that a Petri dish of C. tropicalis had separated out. Into darker and lighter regions suggesting that the. Fungi had formed two separate phenotypes, with. An intriguing similarity to the. “white”. “opaque”. Phenotypes of C. albicans. in. C. albicans, that distinction isn't just. one. Of colour. Also of mating behaviour.

Porman later rejoined the. Lab and led the. Experiments described. in. the. new. Paper published in. Proceedings of the. National Academy of Sciences. what. she, Bennett. Colleagues discovered wasn't only. That C. tropicalis mates and that the. Mating depends on. Pheromones. Also that the. Genetic “switch” that converts the. Fungus from. its. Chaste “white” state to its. More libidinous “opaque” state shares a key gene in. Common with. That in. C. albicans called WOR1.

They determined the. Sequence of necessary. Regulatory events involving WOR1 doesn’t proceed in. Exactly the. Same way in. C. tropicalis as. in. C. albicans. in. C. albicans one. Trigger among several appears to be temperature. the. Team is still. trying. To figure out. what. Turns C. tropicalis on.

“It’s been. really. Hard to find the. Trigger,” Bennett says. “We can’t force the. Switch in. Either direction. We've to just. Plate loads of cells and hope we get. the. one. Random event that switches to the. Other state.”

Finding the. right. Environmental trigger could. Either support or undermine the. Hypothesis that fungus employs sex as. A survival tactic. it. could. Also offer clues to finding the. Presumed mating behaviour of other Candida species.

The National Institutes of Health supported the. Research.

More news from. Brown University: news.brown.edu/

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