The assortments of bacteria that live within the intestines of isolated tribes are far more diverse than the microbes found in the guts of Americans — and scientists say such findings have implications for modern-day maladies ranging from obesity to antibiotic resistance.
The latest studies into the varying genetic signature of microbes found in the intestinal tract — also known as the microbiome — focus on Yanomami Indians in Venezuela's Amazon region as well as on Papua New Guineans. The studies were published this week by Science Advances and Cell Reports, respectively.
In both cases, researchers found a greater variety of bacterial species than is commonly found in industrial societies.
"These findings suggest that lifestyle practices that reduce bacterial dispersal — specifically, sanitation and drinking water treatment — might be an important cause of microbiome alterations," the University of Alberta's Jens Walter, senior author of the Papua New Guinea study, said in a news release.
Sanitation practices are generally a good thing, but scientists say beneficial bacteria are lost along the way. For example, the team behind the research in Venezuela found that the Yanomami tribespeople harbored bacteria that may play a role in boosting immune response and metabolizing carbohydrates. Another example is Oxalobacter formigenes, a microbe that's linked to a decreased risk of kidney stones.
"The challenge is to determine which are the important bacteria whose function we need to be healthy, and have a healthy, educated immune system and a healthy metabolic system," said Maria Dominguez-Bello, a medical researcher at New York University's Langone Medical Center who is the senior author of the study.
'Alarming' antibiotic resistance
Dominguez-Bello and her colleagues also found that the Yanomami tribespeople, who were "uncontacted" by Western visitors until 2009, nevertheless had gut bacteria with genes that could activate resistance to antibiotics. Some of the resistance genes could counter even the third- and fourth-generation synthetic antibiotics created to fight modern diseases.
The researchers say their findings imply that bacteria may possess an ancient but complex set of defense mechanisms that swing into action whenever they come across new threats.
Co-author Gautam Dantas, an immunologist at Washington University School of Medicine, told reporters that the finding was "alarming to us."
"It emphasizes the need to ramp up our research for new antibiotics, because otherwise we're going to lose this battle against infectious diseases," Dantas told reporters.
The gut bacteria were extracted from fecal samples as well as skin swabs and mouth swabs, and then subjected to genetic analysis. The fact that the microbial communities were more diverse is in line with previous studies that have focused on Hadza hunter-gatherers in Tanzania and the Matses people of the Peruvian Amazon.
What's good for the gut
The microbiome has become a topic of increasing interest in recent years, because scientists suspect it plays a crucial role in human health. The best-known illustration of the microbiome's importance is the use of "fecal transplants" to cure a life-threatening intestinal infection known as C. difficile. In the future, microbiome therapy could address autism, obesity, food allergies and immune deficiencies.
Some of the bacteria identified in the guts of the Yanomami "might have therapeutic value" for such conditions, said Jose Clemente from the Icahn School of Medicine at Mount Sinai, another co-author of the study.
Dominguez-Bello emphasized that microbiome studies could help the Yanomami as well as more industrialized societies.
"It seems inevitable that the world is converging to westernized lifestyles," she told reporters, "and so far it has been inevitable to observe how Amerindians when they integrate, or Africans when they westernize — how they quickly suffer our current diseases, obesity, diabetes. So I think that by learning what went wrong with our lifestyle ... we'll also benefit them in not suffering the same health consequences."
In addition to Dominguez-Bello, Dantes and Clemente, the authors of the Science Advances study, "The Microbiome of Uncontacted Amerindians," include Erica Pehrsson, Martin Blaser, Kuldip Sandhu, Zhan Gao, Bin Wang, Magda Magris, Glida Hidalgo, Monica Contreras, Óscar Noya-Alarcón, Orlana Lander, Jeremy McDonald, Mike Cox, Jens Walter, Phaik Lyn Oh, Jean Ruiz, Selena Rodriguez, Nan Shen, Se Jin Song, Jessica Metcalf and Rob Knight.
In addition to Walter, the authors of the Cell Reports study, "The Gut Microbiota of Rural Papua New Guineans: Composition, Diversity Patterns and Ecological Processes," include Inés Martínez, James Stegen, Maria Maldonado-Gómez, A. Murat Eren, Peter Siba and Andrew R. Greenhill.