An Enterobacteriaceae bloom in aging is kept in check by the gut microbiome

The gut microbiome plays important roles in host function and health. Core microbiomes have been described for different species, and imbalances in their composition, known as dysbiosis, are associated with pathology. Changes in the gut microbiome and dysbiosis are common in aging, possibly due to multi-tissue deterioration, which includes metabolic shifts, dysregulated immunity, and disrupted epithelial barriers. However, the characteristics of these changes, as reported in different studies, are varied and sometimes conflicting. Using clonal populations of C. elegans to highlight trends shared among individuals, raising them in different microbial environments and employing NextGen sequencing, CFU counts and fluorescent imaging to characterize age-dependent changes in gut microbiome composition, identified a bloom in Enterobacteriaceae bacteria, which was independent of initial conditions and associated with chronological aging. Experiments using the commensal Enterobacter hormachei as representative suggested that the Enterobacteriaceae bloom was facilitated by a decline in Sma/BMP immune signaling in aging animals and demonstrated detrimental potential for increasing susceptibility to infection. However, such detrimental effects were context-dependent, mitigated by competition with commensal communities, which are thus highlighted as determinants of healthy versus unhealthy aging, depending on their ability to keep in check opportunistic pathobionts.