When human bodies decay, they all share this interesting feature

The kind of microbiome present when a human dies and decomposes – that is, the combination of microscopic organisms including bacteria and tiny fungi – is universal regardless of location or environmental conditions, according to international researchers who say the findings could help forensic scientists. The team tracked the decomposition process of 36 human bodies that had been donated to science, burying them in three locations in different climates across each of the four seasons. They found that around decomposing human bodies, a particular group of microbes would always appear, regardless of location, climate, or season, and are otherwise rare in non-decomposition environments. After reconstructing a network of interactions found at the sites, the team found fungi and bacteria might be spread through insects, and share resources to metabolise the products of decomposition. The team also used this information along with machine learning to predict time since death, which could have future applications for forensic science.

Journal/conference: Nature Microbiology

Link to research (DOI): 10.1038/s41564-023-01580-y

Organisation/s: Colorado State University, USA

Funder: Funding was provided by the National Institutes of
Justice (2016-DN-BX-0194, J.L.M.; 2015-DN-BX-K016, J.L.M.; GRF STEM
2018-R2-CX-0017, A.D.B.; GRF STEM 2018-R2-CX-0018, H.L.D.), the
Canadian Institute for Advanced Research Global Scholar Program
(J.L.M.), National Science Foundation Early Career Award (1912915,
K. C. Wrighton) and National Institutes of Health T32 Training Award
(T32GM132057, V.N.).

Media release

From: Springer Nature

1.  Microbiology: Microbes responsible for human decomposition could help forensics

A component of the microbiomes associated with decomposing human cadavers are universal regardless of location or environmental conditions, a paper published in Nature Microbiology suggests. The findings show a conserved and predictable sequence of microbial interactions that break down organic matter, which could have implications for forensic science.

Decomposition is a fundamental process that recycles dead biological material to fuel biological processes, such as plant productivity and soil respiration. Microbial fungi and bacteria are predominantly responsible for decomposition, and although this process is well studied, research has focused predominantly on the breakdown of dead plant biomass. In contrast to plants, animal carcasses, including those of humans, are enriched in readily decomposable proteins and lipids, but their impact on biogeochemistry and community ecology are poorly understood.

Jessica Metcalf, Zachary Burchman, and colleagues tracked the decomposition process in 36 human cadavers, which had been willed to science. The bodies were placed in three locations with either a temperate or semi-arid climate, with three cadavers placed at each location for each of the four seasons, and the researchers took samples of the cadavers’ skin and surrounding soil throughout the first 21 days postmortem. Metcalf and colleagues found that decomposing human cadavers had a universal consortium of microbes, regardless of the location, climate or season, that are rare in non-decomposition environments and appear unique to the terrestrial breakdown of flesh.

With metagenome-assembled genomes and metabolomic profiling of soils adjacent to cadavers, the authors reconstructed a network of interactions that revealed how fungi and bacteria share resources as they metabolize decomposition products. Metcalf and colleagues suggest that insects may serve as vectors that disperse these microbes from one decomposing animal to another.

Using data on the microbial timeline of cadaver decomposition, combined with a machine learning model, the authors were also able to predict time since death, which could have potential future applications for forensic science.


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