We think humans rule the world, but the reality is that Earth is dominated by microbes. Microbes are mostly single-celled creatures, and they have existed on Earth for more than 3.5 billion years. They occupy almost every ecological niche — from hot springs in Yellowstone, to acidic mine waste, even on and in our bodies, where they outnumber our cells by more than 100 times. Humans have used these diverse creatures for millennia. Bread, cheese, yogurt, beer and wine are among the vast array of food products that utilize microbial action. In industry, microbes are used to produce chemicals, make our favorite foods and even to clean up oil spills.
Some microbes called pathogens can cause disease in humans, including dental decay, skin infections, and intestinal disease. It is thought that up to 60 percent of all cancers have a microbial origin. Microbes are truly a Jekyll and Hyde dilemma for humans.
Recently, there has been a report of a microbe which may represent both sides of this Jekyll and Hyde equation. Recent genomic sequencing has found that an industrial species of yeast is essentially identical to another yeast capable of causing yeast infections in humans.
The human pathogen is a yeast known as Candida krusei, which is responsible for up to two percent of yeast infections globally. To contribute to the misery, it is resistant to the most common antimicrobial used to treat these yeast infections, called fluconazole. Antimicrobial resistance makes it more difficult to treat infections and adds to the cost of treatments.
On the industrial side, a yeast called Pichia kudriavzevii is used to make fermented foods and specialty beer. It is used in the production of chocolate, where fermentation with this yeast removes the bitter taste present in the raw cacao beans. It has also been genetically altered to produce specific chemicals and bioethanol. There are also at least two other yeasts with different names used in industrial applications that are likely this same microbe.
Identification of yeasts is further complicated because some yeasts can have both sexual and asexual forms, which changes some of their properties and their appearance under a microscope. However, genomic sequencing has made identification of microbes easier and has yielded some surprises. For example, 30 different strains of Candida krusei and Pichia kudriavzevii were found to be greater than 99.5 percent genetically identical, indicating that they’re the same species. This is surprising because one is considered an environmental microbe and the other a human pathogen.
Is this a curiosity or something we should be concerned about? Using a yeast that’s a potential human pathogen in industrial processes, and food production could be an issue for workers that are exposed to it. Heightening the concern is that all strains were resistant to fluconazole, the most common drug used to treat these infections.
Technological progress brings big benefits and sometimes surprises. We continue to celebrate advances that help us discover more about ourselves and other organisms. We also need to stay vigilant as to new information that helps us identify new and old hazards.