Impact of radiation dose and time since radiation exposure on host-microbe relationship

The microorganisms that colonized in or on hosts play significant roles in regulating host's immunological fitness and bioenergy production, thus controls the host's response to stress or foreign stimuli. Since radiation typically causes a pro-inflammatory and bioenergy expensive condition, we speculate that the radiation could influence gut microbial compositions, thereof the host-microbe bidirectional relationship. Pertinent model included exposing the young adult mice to total body irradiation (TBI) at doses of 9.5Gy and 11Gy, respectively. Descending colon contents (DCC) were collected from non-irradiated mice (baseline control), and irradiated mice euthanized on days 1, 3 and 9 post-TBI. DCC's 16s ribosomal DNAs were screened for bacterial taxonomic classification and bacterial abundance profile informed metagenome-specific biofunctions. A second aliquot of same DCC was screened for untargeted metabolomics assay to find most perturbed metabolite-enriched networks. Dose-independent temporal delay since TBI emerged as the primary factor explaining the increased richness of bacterial community and the diversity of metabolite landscape. Among the mice exposed to 11Gy TBI, an increased abundance of Firmicutes, an anti-inflammatory and efficient energy harvesting bacteria accompanied an increment of pro-inflammatory Deferribacteres. Systems evaluation of the functional networks linked to DCC's metagenome and metabolite, respectively, suggested a diverging trend between host and DCC microbes in regulating the network clusters, such as lipid metabolism, bioenergy synthesis, particularly at the later time points post-11Gy TBI. This analysis potentially suggested a disrupted symbiotic relationship between the host and microbes when the host became moribund. Overall design: 38 samples with different amounts of radiation and time points