An investigation of intrinsic and extrinsic factors that influence soil microbial succession during human decomposition

Decomposer organisms play a vital role in terrestrial nutrient cycling, breaking down complex organic compounds and providing nutrients for primary producers. Microbial communities and other decomposers associated with a vertebrate carcass, or the “necrobiome”, are critical for degradation and recycling of soft tissues following vertebrate mortality. The impact of microbial decomposers in vertebrate decomposition has been shown with regard to soil microbial communities, where the presence of soil microbes impact decomposition rate and undergo succession. However, current assessments of microbial ecology within decomposition-impacted soils have primarily focused on one aspect of microbial succession: succession of bacterial taxa for forensic applications. While this has provided a foundation of knowledge to build upon, it is still unclear how this succession is affected by extrinsic (e.g., environmental) and intrinsic (e.g., cadaver-related) factors and how microbial functions are impacted. These knowledge gaps are important for understanding how ecosystem processes are impacted by decomposition. The ultimate aim of this body of research was to improve our understanding of soil microbial succession during decomposition by assessing these knowledge gaps. Thus, this dissertation consisted of three research objectives: (1) evaluation of the effects of intrinsic factors on soil microbial succession, (2) evaluation of the effects of extrinsic factors on soil microbial succession, and (3) evaluation of soil microbial functional succession during decomposition. Two separate field studies were conducted. The first observed the early stages of decomposition of 19 subjects, while the second observed a longer term (one year) decomposition of three subjects. All subjects decomposed on the soil surface at the University of Tennessee Anthropology Research Facility. Overall, we show that soil microbial succession during decomposition is impacted by both intrinsic and extrinsic factors. This included body mass index, which affected soil chemical response and microbial succession, making it a factor of interest for future investigations. We also used metatranscriptomics to show that microbial gene expression shifted during decomposition and was still impacted following one year. Together, our investigation of factors that influence multiple aspects of microbial succession lays an important framework for understanding the ecology of human and vertebrate decomposition in terrestrial ecosystems.