Can bacteria tell time? When it comes to time of death, they might be able to in the near future.

Determining the time of death is one of the most common challenges facing forensic scientists. Many factors contribute to the variability in decay rate of remains, so observations in addition to the stage of decomposition must be considered in order to estimate this critical piece of information.

Additional evidence used includes easily visualized observations such as the presence of rigor mortis and insect infestation, while others are not as easy to see such as the temperature of the body and soon - the presence of microorganisms.

Both endogenous and environmental microbes play a large role in the breakdown of remains, and researchers have begun characterizing the types of microorganisms present throughout the different stages of decomposition to uncover any patterns of growth. Mouse , pig , and now human cadavers have been sampled for microbes throughout decomposition.

DNA was extracted from the samples taken at different stages and used to determine the type and abundance of microorganisms present by next generation DNA sequencing.

Bloat was the stage of decomposition on which these studies largely focused. During this stage, anaerobic microbes take over and produce gases within the body cavity, causing the expansion of the abdomen. The pressure buildup from these gases leads to a purging event which then re-exposes the internal body cavity to oxygen and changes the microbial profile once again.

All studies showed the presence of large Firmicutes and Proteobacteria populations with Actinobacteria and Bacteroidetes also found in smaller but significant numbers. Although these population types were common to all, variation was seen in abundance of these organisms among species and between cadavers.

Although there is much more work to do in order to create a useful tool for forensic scientists, the ability to see distinct bacterial communities emerge as decomposition progresses is a promising beginning to the possibility of microbes telling time.

Alyssa Conly