Death and decomposition usher in a complex community of decomposers to break down and recycle organic matter. Two understudied, key players in this necrobiome are postmortem microbiota and necrophagous insects. The objectives of this study were to characterize these interkingdom dynamics within two postmortem contexts: 1) active insect colonization and carrion decomposition in contrasting seasons; and 2) a snapshot of human infant microbiota pre-insect colonization, to investigate their potential to inform forensic science, carrion ecology, and human health. It was predicted that postmortem microbial communities would change over time and by season. It was also hypothesized that active insect colonization of carrion by blow flies would facilitate the introduction of microbes, altering carrion microbiota. For microbiomes pre-insect colonization, it was predicted that microbiome composition would be structured by body site microbiota and manner of death (MOD), which could indicate potential biomarkers related to MOD. Seasonal comparisons demonstrated significantly distinct microbiota over time and between carcass and fly microbes and significantly slowed decomposition in the fall, greater blow fly diversity in the fall, increasing alpha diversity over decomposition time in the summer, and evidence for the introduction of microbes by flies. In addition, manner of death and body site had a statistically significant structuring effect on postmortem microbiota, and significant interactions (age, race, sex) were identified with manner of death. A potential biomarker of infant death, Sneathia, associated with preterm birth and labor was also discovered. These studies present new data that further our understanding of complex postmortem microbiome dynamics and promote standardization of practical and applicable analyses within the fields of forensic science and carrion ecology.
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