Microbes: The Key to Determining Time of Death

Thursday - February 15 2024, 09:32 UTC - 9 months ago

New research has identified 20 microbes that are consistently present on all 36 decomposing bodies, aiding in pinpointing time of death. These microbes also attract scavengers and shift their metabolism, and are influenced by climate and location. Understanding these changes has potential applications in forensics and medical fields.

There are various methods used for determining the time of death, also known as the postmortem interval (PMI). One of the most common ways are measuring the body temperature and rigor mortis, which is when the body’s muscles stiffen. Another method, still under development, are microbes. As the body begins to decompose, microbial communities undergo predictable changes in composition and abundance over time. By studying these microbial changes, forensic scientists may be able to estimate the time since death.

In a new study, researchers have identified 20 microbes that are found in bodies at specific times during decomposition. These microbes can help in pinpointing when exactly a person died. "It’s really cool that there are these microbes that always show up to decompose animal remains," said Jessica Metcalf, Associate Professor at the Colorado State University, and the senior author of the study. "Hopefully, we’re busting open this whole new area of ecological research." They investigated 36 bodies that were closely monitored for their microbial changes as they decomposed in different climates and seasons. Surprisingly, their findings revealed a consistent set of 20 microbes present on all 36 bodies, regardless of the environmental conditions or soil types. Even more intriguingly, these microbes appeared to arrive simultaneously across all cadavers, suggesting a universal pattern in the decomposition process.

But how do insects get inside the body? As bodies decompose, they release nutrients that affect the surrounding environment and plant life. These nutrients, like nitrogen, carbon, and phosphorus, come mainly from proteins and lipids in the body. The scientists studied these nutrients and found their presence in the skin and soil around the body. Over time, certain compounds from the body, like fatty acids and amino acids, became more abundant in the soil. The influx of nutrients from the decomposing body disturbs the environment and attracts scavengers, initiating the assembly of specific microbial communities. "We see similar microbes arrive at similar times during decomposition, regardless of any number of outdoor variables you can think of," Metcalf said. These microbes shift their metabolism to efficiently use available resources, like amino acids and carbohydrates.

But climate also plays a role. The researchers found that climate, location, season, and decomposition stage all significantly influenced the ecology of microbial decomposers in the soil. For example, the composition of microbial communities varied depending on whether the climate was temperate or semi-arid, as well as the specific location. They discovered a universal network of microbes involved in decomposition, regardless of the region or environment. "Understanding the ecology of microbial decomposition has both immediate applications in forensics and future potential for broader applications," Metcalf said. "Estimating time since death is important in forensic investigations, but so is the ability to identify individuals. I would love to bring this work into medical applications related to living individuals, communities, and urban systems." .