The samples are all kefir cheese, made from kefir milk, a traditional beverage produced by fermenting milk using kefir grains. Fermentation is an ancient practice involving the chemical breakdown of substances by bacteria, yeast, or other microorganisms.
The lifestyle of the Xiaohe population can be researched more accurately when DNA information is recovered from these ancient, fermented dairy remains, and scientists can explore the co-evolution between the fermented bacteria and their hosts.
DNA was captured from the fermented cheese samples to reconstruct the genome of Lactobacillus kefiranofaciens – a fermentative bacterium identified exclusively from kefir cheese and grains.
Kefir begins its life with a culture that is then made into more kefir so as the cheese spread from place to place so did the cultures used to make it. To retrace the probiotic microbe’s journey, the researchers compared the DNA of the L. kefiranofaciens found in the mummies’ cheese with that of others in the family tree finding two separate branches. The cemetery kefir strains have been related to those from Tibet and East Asia. This shows people from this region may have been migrating to Tibet, a migration route that had previously not been considered.
They found varying levels of bacterial species in the three different samples. The species found in these samples are found in present-day kefir grains, fermented food, dairy contamination, and the environment. This is unexpected because we would anticipate finding a variety of contaminant bacteria in these ancient samples because of thousands of years of exposure to the environment.
They have also found that making kefir cheese not only extended the shelf life of raw milk but reduced the level of lactose in dairy products. This made dairy more palatable because many people from this region had an intolerance to lactose.
The samples have also suggested the mingling of ancient peoples as DNA from cows and goats have been found in different cheeses. The goat DNA is like that of other ancient Central Asian samples, suggesting it may have been part of a group of domesticated goats that became widely distributed, Fu says.
The study of this cheese, published in the journal Cell has allowed scientist to hypothesise about migration, mingling of different ancient communities and why and how the ancient fermentation process was undertaken.
