Those funky cheese smells allow microbes to 'talk' to and feed each
other
Researchers discover that bacteria that ripen cheese respond to the
volatile gases produced by cheese fungi

Date:
October 16, 2020
Source:
Tufts University
Summary:
Researchers found that bacteria essential to ripening cheese can
sense and respond to compounds produced by fungi in the rind and
released into the air, enhancing the growth of some species of
bacteria over others.

The make-up of the cheese microbiome is critical to flavor and
quality of the cheese.



FULL STORY ========================================================================== Researchers at Tufts University have found that those distinctly funky
smells from cheese are one way that fungi communicate with bacteria, and
what they are saying has a lot to do with the delicious variety of flavors
that cheese has to offer. The research team found that common bacteria essential to ripening cheese can sense and respond to compounds produced
by fungi in the rind and released into the air, enhancing the growth
of some species of bacteria over others. The composition of bacteria,
yeast and fungi that make up the cheese microbiome is critical to flavor
and quality of the cheese, so figuring out how that can be controlled
or modified adds science to the art of cheese making.


==========================================================================
The discovery, published in Environmental Microbiology, also provides a
model for the understanding and modification of other economically and clinically important microbiomes, such as in soil or the gastrointestinal tract.

"Humans have appreciated the diverse aromas of cheeses for hundreds of
years, but how these aromas impact the biology of the cheese microbiome
had not been studied," said Benjamin Wolfe, professor of biology in the
School of Arts and Science at Tufts University and corresponding author
of the study. "Our latest findings show that cheese microbes can use these aromas to dramatically change their biology, and the findings' importance extends beyond cheese making to other fields as well." 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 a heavy rain in forests. As bacteria and fungi
grow on ripening 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 those biological products contribute to the flavor and aroma of cheese and they are the reason
why Camembert, Blue cheese and Limburger have their signature smells.

The Tufts researchers found that VOCs don't just contribute to the sensory experience of cheese, but also provide a way for fungi to communicate with
and "feed" bacteria in the cheese microbiome. By pairing 16 different
common cheese bacteria with 5 common cheese rind fungi, the researchers
found that the fungi caused responses in the bacteria ranging from strong stimulation to strong inhibition. One bacteria species, Vibrio casei,
responded by growing rapidly in the presence of VOCs emitted by all
five of the fungi. Other bacteria, such as Psychrobacter, only grew
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 enhanced, called the
glyoxylate shunt, allows the bacteria to utilize more simple compounds
as "food" when more complex sources such as glucose are unavailable. In
effect, they enabled the bacteria to better "eat" some of the VOCs and
use them as sources for energy and growth.

"The bacteria are able to actually eat what we perceive as smells,"
said Casey Cosetta, post-doctoral scholar in the department of biology at
Tufts University and first author of the study. "That's important because
the cheese itself provides little in the way of easily metabolized sugars
such as glucose. With VOCs, the fungi are really providing a useful assist
to the bacteria to help them thrive." There are direct implications of
this research for cheese producers around the world. When you walk into
a cheese cave there are many VOCs released into the air as the cheeses
age. These VOCs may impact how neighboring cheeses develop by promoting
or inhibiting the growth of specific microbes, or by changing how the
bacteria produce other biological products that add to the flavor. A
better understanding of this process could enable cheese producers
to manipulate the VOC environment to improve the quality and variety
of flavors.

The implications of the research can even extend much further. "Now
that we know that airborne chemicals can control the composition of microbiomes, we can start to think about how to control the composition
of other microbiomes, for example in agriculture to improve soil quality
and crop production and in medicine to help manage diseases affected by
the hundreds of species of bacteria in the body," said Wolfe.


========================================================================== Story Source: Materials provided by Tufts_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Casey M. Cosetta, Nicole Kfoury, Albert Robbat, Benjamin
E. Wolfe. Fungal
volatiles mediate cheese rind microbiome assembly. Environmental
Microbiology, 2020; DOI: 10.1111/1462-2920.15223 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201016164320.htm

--- up 7 weeks, 4 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)