They live in caves and springs throughout Mexico and thrive in water so toxic that most forms of life die within minutes.
Meet the Atlantic molly -- an extremophile fish that lives in toxic water full of hydrogen sulfide from natural oil deposits and volcanic activity environments. A 10-year collaborative project led by biologists from Kansas State University and Washington State University has discovered how the fish can survive.
The answer: It's all in the genes. The research appears in Molecular Biology and Evolution.
"Learning how these extremophiles function tells us something very fundamental about life itself," said Michael Tobler, Kansas State University assistant professor of biology involved in the project. "We are able to learn about the boundaries where life can exist, which tells us something basic about how cells and organisms work."
The tiny Atlantic molly can live in small puddles of toxic or nontoxic water. Using genomic tools, the researchers compared gene expression of the mollies living in toxic hydrogen sulfide environments with those mollies living in nontoxic environments just a few yards away.
They found that the fish have a two-pronged approach to survival: They become inert to the toxins that enter the body and they are able to detoxify hydrogen sulfide more efficiently.
Hydrogen sulfide shuts down energy production in cells by interfering with specific proteins. The fish combat this challenge by using anaerobic metabolism, which is an alternative -- although much less efficient -- way to produce energy and does not involve oxygen.
The scientists found that about 170 of the fish's 35,000 or so genes were turned on, or upregulated, to detoxify and remove the hydrogen sulfide. The poison invades the fishes' bodies, but their changed proteins help the fish break down the hydrogen sulfide into nontoxic forms and excrete it.
"It's not that they're keeping the hydrogen sulfide out," said Joanna Kelley, a genome scientist at Washington State University and collaborator on the project. "It's not that they are necessarily turning on some other unrelated genes. It's really that the genes that have been previously implicated in hydrogen sulfide detoxification are turned on or turned up. That's really the exciting part."
As part of the collaborative project, Tobler studied the toxic environments and fish physiology while processing sulfur. Because hydrogen sulfide is toxic to nearly all living creatures, Tobler and his collaborators had to wear protective gear and respirators to study the fish in toxic habitats
"Comparing the fish in sulfidic and nonsulfidic environments helps us learn about the physiological processes that are involved in processing these molecules," Tobler said. "We can use this knowledge for developing biomedical applications."
While hydrogen sulfide is toxic in high concentrations, it is fundamental for life at low concentrations. When human cells do not produce enough sulfide, it can lead to health problems, such as cardiovascular disease, inflammation and brain function issues. Biomedical research is developing drugs that modulate hydrogen sulfide production in humans to prevent health issues, Tobler said, and the Atlantic molly provides a good model.
The research is also important for understanding the long-term effects of human-caused change and pollution, Tobler said, because the Atlantic molly appears in naturally occurring toxic water.
"In these habitats, the natural pollutants give us a glimpse into the future and help us think about what happens in ecosystems that suffer from human-induced changes or pollution," Tobler said. "We can learn how an ecosystem changes when pollutants are added and how organisms cope with that."
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