decomposition process, but are only now learning that some of the “less visible” biotic factors, e.g., microbes, more specifically bacteria, are key factors in the process. The utilization of next-generation genetics has led to novel discoveries associated with microbial diversity, particularly bacteria, associated with decomposing vertebrate remains. For example, research from the Department of Entomology, Texas A&M University has determined the importance of bacterial succession on pig carrion − within the first five days of the animal’s demise. It is estimated that in 62% of cases, the time since death can be explained by the bacterial communities that are present (Pechal et al., 2013). Microbes release many of the volatiles associated with the decomposition process, such as indole, dimethyl disulfide, cadaverine and putrescine, at the time of death or soon thereafter (Vass et al., 2002). A number of insects have evolved highly sensitive olfaction systems that allow them to detect, locate and evaluate the remains as potential food for their offspring (Easton & Feir, 1991). Such sensitivity gives them survival advantages, as availability of carrion is unpredictable, usually present for only a short period of time (depending on the time of year and location) and highly competed for by other fauna. So if not located quickly, insects miss the opportunity to deposit their offspring in this rich environment.
An understanding of the microbial community structure during decomposition could enhance our ability to determine time of death. This information has led to new techniques for estimating the time of death of a person based simply on what insects are arriving at remains at given time points after death. Such approaches are revolutionizing the field of forensic entomology, as practitioners are no longer limited to those arthropods feeding on the remains, but can now utilize those insects attracted to the human body and the microbes they interact with to determine time of death. Determining if human remains have been moved from one location to another is also critical for forensic investigations and microbes could prove to be a critical tool for such purposes (pages 26-29). Presently, we are witnessing the bridging of multiple disciplines within the forensic sciences to better understand how human remains decompose. Entomology and microbiology serve as a model of how such collaborations result in advancements, and applications, vital to solving crime globally; however, Figure 2 Black vulture, Coragyps atratus, scavenging a white-tailed deer, Odocoileus virginianus, carcass. (Courtesy of Dr Tawni Crippen.)
Furthermore, research is demonstrating that volatiles from microbes could be playing a major role in regulating insect succession (shifts in insect community structure, e.g., the number of species present) on vertebrate carrion. More simply put, the odours emitted from microbes on decomposing remains are regulating which insects colonize human remains at different time points after death of the individual. Additionally, necrophagous flies competing for the same remains are attracted or repelled by volatiles released by microbes associated with other species of flies. So the temporal appearance of fly species and their possible deposition of bacterial species onto decomposing remains may ultimately influence the bacterial community structure present. This is significant because such an influence may also affect insect succession during decomposition.
The utilization of nextgeneration genetics has led to novel discoveries associated with microbial diversity www.sfam.org.uk
microbiologist
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September 2015
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