This is an interesting study; you'll have to actually look at the open access paper to see the meat of it, which is the various graphs showing the changes in relative population size of different microbe families in the gut that take place with age. A great deal of work on the gut microbiome and its role in health and aging is presently taking place in the scientific community; researchers have identified a number of beneficial metabolites that are produced by classes of microbe that decline with age. Further, the gut microbiome becomes ever more inflammatory with age. The size of these effects on health might be in the same ballpark as those of regular exercise, but the reasons why changes take place are not yet fully understood. The causative mechanisms seem fairly clear in and of themselves, meaning declining immune function, changes in diet, and so forth, but how they interact and which are primary and which are secondary is yet to be firmly resolved.

We obtained RNA sequencing data of subjects ranging from newborns to centenarians from a previous study, and summarized the data into a relative abundance matrix of genera in all the samples. Without using the age information of samples, we applied an unsupervised algorithm to recapitulate the underlying aging progression of microbial community from hosts in different age groups and identify genera associated to this progression. Literature review of these identified genera indicated that for individuals with advanced ages, some beneficial genera are lost while some genera related with inflammation and cancer increase.

A few genera were previously implicated in the literature, such as Oxalobacter, Butyrivibrio, Lactobacillus which have been experimentally demonstrated to be associated with aging, as well as Prevotellaceae which has been highlighted with lower presence in the gut microbiota of centenarians. The abundances of some other genera increased with respect to aging, but decreased in the extremely elderly subjects. Among these genera, Lactobacillus species are commonly used as probiotics. Oscillospira species have been frequently reported as enriched in lean subjects compared to the obese subjects, and are central to the human gut microbiota for degrading fibers. Oxalobacter is responsible for degrading oxalate in the gut. It has been experimentally demonstrated appearing in the gut of almost all young individuals, but these bacterium may later be lost during aging.

Prevotellaceae is commonly found in the gastric system of people who maintain a diet low in animal fats and high in carbohydrates and is lost in centenarians. Researchers also found that there was an increased abundance of Prevotellaceae in the guts of healthy people compared with people with Parkinson's disease. Parascardovia is a genus of Bifidobacteriaceae, which has been shown to provide health-promoting benefits to the host. Butyrivibrio species have been experimentally proved as butyrate producing bacteria, and butyrate is a preferred energy source for colonic epithelial cells and is thought to play an important role in maintaining colonic health in humans. Overall, the decrease of these beneficial genera in the elderly age groups, especially centenarians, maybe manifestation of or causal associations to decline of health in those age groups.