Researchers at Tufts University have found that these distinctly funky odors from cheese are a way for fungi to communicate with bacteria, and what they say has a lot to do with the delicious range of flavors that cheese has to offer. The research team found that common bacteria that are important for the maturation of cheese can feel and react to compounds produced by fungi in the shell and released into the air, which enhances the growth of some species of bacteria compared to others. The composition of bacteria, yeasts and fungi that make up the cheese microbiome is critical to the taste and quality of the cheese, so figuring out how to control or modify it adds science to the art of making cheese.
The discovery, published in Environmental microbiology, also provides a model for understanding and modifying other economically and clinically important microbiomes, such as in the soil or gastrointestinal tract.
“Humans have valued the different aromas of cheese for hundreds of years, but how these aromas affect the biology of the cheese microbiome had not been studied,”
Many microbes produce airborne chemical compounds called volatile organic compounds or VOCs as they interact with their environment. A widely recognized microbial VOC is geosmin, which is emitted by soil microbes and can often be smelled after heavy rain in the forests. When bacteria and fungi grow on mature cheeses, they secrete enzymes that break down amino acids to produce acids, alcohols, aldehydes, amines and various sulfur compounds, while other enzymes break down fatty acids to produce esters, methyl ketones and secondary alcohols. All of these organic products contribute to the taste and aroma of cheese, which is why Camembert, Blue cheese and Limburger have their signature scent.
The Tufts researchers found that VOC not only contributes to the sensory experience of cheese, but also provides fungi with a way to communicate with and “feed” bacteria into the cheese’s microbiome. By pairing 16 different common cheese bacteria with 5 common cheese-skin fungi, the researchers found that the fungi caused reactions in the bacteria, ranging from strong stimulation to strong inhibition. One bacterial species, Vibrio casei, responded by growing rapidly in the presence of VOCs emitted by all five fungi. Other bacteria, such as Psychrobacter, grew only in response to one of the fungi (Galactomyces), and two common cheese bacteria decreased significantly in number when exposed to VOCs produced by Galactomyces.
The researchers found that the VOCs altered the expression of many genes in the bacteria, including genes that affect the way they metabolize nutrients. One metabolic mechanism that was improved, called the glyoxylate shunt, allows the bacteria to use simpler compounds such as “food” when more complex sources such as glucose are not available. In fact, they allowed the bacteria to better “eat” some of the VOCs and use them as energy sources and growth sources.
“The bacteria are able to actually eat what we perceive as odors,” said Casey Cosetta, a postdoctoral fellow in the Department of Biology at Tufts University and first author of the study. “This is important because the cheese itself provides little in the way of easily metabolized sugars such as glucose. With VOCs, the fungi really provide a helpful aid to the bacteria to help them thrive.”
There are direct implications of this research for cheese makers worldwide. When you enter a cheese cave, many VOCs are released into the air as the cheeses age. These VOCs can affect how neighboring cheeses develop by promoting or inhibiting the growth of specific microbes or by altering how the bacteria produce other biological products that add to the taste. A better understanding of this process can allow cheese makers to manipulate the VOC environment to improve the quality and variety of flavors.
The implications of research can even extend much further. “Now that we know that airborne chemicals can control the composition of microbiomes, we can start thinking about how we can control the composition of other microbiomes, for example in agriculture to improve soil quality and crop production and in medicine for to help deal with diseases that are the hundreds of species of bacteria in the body, “Wolfe said.
Cheese: New insight into an ancient food
Casey M. Cosetta et al., Fungal volatile mediated cheese shell microbiome collection, Environmental microbiology (2020). DOI: 10.1111 / 1462-2920.15223
Provided by Tufts University
Citation: These funky cheese smells allow microbes to ‘talk’ and feed each other (2020, October 16) retrieved October 18, 2020 from https://phys.org/news/2020-10-funky-cheese-microbes.html
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