By  Jayani Rathnayake  
Did you know that bacteria also celebrates seasonality changes as other living organisms in modern hierarchy? Much like the weather, some human stomachs change throughout the year. The gut bacterial fluctuations, at first time, has been found by Dr Sonnenburg and his colleagues, a microbiologist at Stanford University and lead author of the new study.   

In Tanzania, not far from the Serengeti, live the Hadza, a community of about 1,300 people. For such a small group, they attract a lot of scientific attention. Dr. Sonnenburg found that microbiota of these people reflects the seasonal availability of different types of food. Between seasons striking differences were observed in their gut microbial communities, with some taxa are suddenly disappearing only to reappear when the seasons turned. Further comparison with Hadza microbiota with that of diverse urbanized people revealed distinctly different patterns of microbiota community composition. Many gut bacteria that wax and wane drastically are rare in people living in industrialized societies. They discovered that the Hadza microbiome is seasonal, changing in a cycle throughout the year. Diversity peaks in the dry season, when Prevotella species become particularly abundant and the bacteria that showed the greatest annual fluctuations generally tended to be strains not present in the gut of people with Western lifestyles. These annual changes in the gut microbiome are probably caused by cyclical shifts in the Hadza diet. During Tanzania’s dry season, the Hadza eat a lot of meat plus tubers and fruit from the baobab tree, but in the wet season they eat more honey and berries. Prevotella species are particularly good at breaking down plant material, so may be particularly useful during the dry season.   

In 2013, Stephanie Schnorr, then a graduate student at the Max Planck Institute for Evo lutionary Anthropology in Leipzig, Germany, began the first study of the Hadza microbiome. She collected a series of stool samples. Dr. Schnorr eventually extracted DNA from microbes within 27 Hadza and compared them with samples gathered from people in Bologna, Italy. In 2014, she and her colleagues reported some striking differences. The Hadza hosted a much greater diversity of gut microbial species than did the Italians, the researchers found, and there were some fundamental differences in species they carried. Some that were common in the Hadza were rare or missing from Italians.Some samples were collected during Tanzania’s dry season and others during the wet season. Dr. Sonnenburg oversaw an analysis of those samples from 188 of the Hadza. In the new study, published in the journal Science, he and his colleagues reported sharp fluctuations in composition of the gut bacteria. Some species were more common in one season than the other,some simply disappeared altogether. A comparison of these samples with those taken by Dr. Schnorr confirmed the fluctuations to be a regular cycle.   

“In terms of the structure that has to be done to see whether the Hadza microbiome, we can say we have a transplanting bacteria’ Dr. Schnorr said. But the discovery of a seasonal cycle is new for any human microbiome. Researchers already knew that the composition of gut bacteria can shift quickly. “An abrupt change in diet will lead to an abrupt change in the gut microbiome, in the order of a day or two,” Dr. Sonnenberg said. In the new study, Dr. Sonnenburg and his colleagues also compared the Hadza microbiome with those of people in 17 other societies, including urban Americans ‘ and Yanomamo villagers in the Amazon rain forest.The Hadza microbiome is most similar to those in traditional societies, and least to the industrialized ones. The researchers found that the species that set the Hadza apart from industrial societies the most are also the ones that are the most seasonal.   
It has been proven that the study sheds light on how the seasonal availability of plants and animals might have influenced the gut microbes of our ancient human ancestors, who would have hunted and gathered in a similar fashion to the Hadza. Knowing this could help researchers understand where ancestral humans lived and foraged, as well as which nutrients were available to them. It also suggests the human evolved in a ‘bio rhythm’ in sync with natural food cycles, moreover, that industrialized people’s microbiomes could be out of sync with that cycle. There are not yet enough data to determine how that affects our gut health, ‘ though, they said. It is thought that certain health problems may arise because our bodies may not be well adapted to the microbiomes associated with Western diets and lifestyles.   
(The writer is a medical student 
at the University of Colombo)