Death does not always signal the end of life

Monday, 26 July, 2004

Biochemistry PhD student David Carter is examining cadaver breakdown and soil biology to provide answers to life's toughest question; what happens to us after we die?

"There has been considerable research focusing on the breakdown of organic material such as leaves, branches, and fruit, in the soil, but very little work has been done on the decomposition processes and nutrient cycling associated with cadavers in soil," Carter said.

Cadaver breakdown and decomposition is a somewhat different process to that of plant-derived organic matter. Cadavers contain a greater proportion of protein and fat than plant materials. Also, and more importantly, a large internal microbial population exists within the cadaver which is credited with initiating and fuelling decomposition.

When a cadaver makes contact with the soil, the relationship between body microbe and soil microbe activity during decomposition is virtually unknown.

"We want to observe the interaction between the microbes we already carry within us with the microbes waiting for us in the soil," he said.

"Exactly which microbes dominate in number and activity at a certain stage of decay on a cadaver is unknown," he said.

Whether it is internal microbe activity from the cadaver, external microbe activity from the soil, or a dynamic interaction between the two, Carter hopes to map the progress of cadaver breakdown by giving the culprits names and numbers.

This is achieved using two tests, carried out on the soil associated with the remains of rats.

The first, phospholipid fatty acid analysis, is used in this instance to identify how the structure of the microbe community immediately surrounding a cadaver changes or evolves as the decomposition of the body proceeds. For instance, how the proportion of fungi to bacteria adjusts through the stages of breakdown.

The second, denaturing gradient gel electrophoresis, is a DNA-based technique that should provide an analysis of the complexity of the bacterial community. That is, identifying the specific players in the microbial decomposition process.

This gives the microbes involved in decomposition names and numbers, however Carter believes it may also hold the key to identifying the 'when' component of the process. Being able to pinpoint a time of death, or time of burial after death, would have enormous forensic applications.

It is hypothesised that successive sequences of microorganisms may act as a basis for estimating a postmortem and post-burial interval.

"It would be like using aspects of nature to solve forensic crimes," Carter said.

"To achieve this it is necessary to examine the rate of cadaver mass loss, as well as the structure and function of the soil microbial population, over time in field and laboratory settings," he said.

Carter hopes his attempts to introduce soil biology and biochemistry to forensic science will provide a greater understanding of the contribution cadaver breakdown makes to terrestrial ecosystem function.

Being somewhat of a pioneer in this field of study, he also hopes his work will stimulate further research into this largely unknown body of science.

Carter fully appreciates the role decomposition plays in a healthy ecosystem, even though the results may be too much for many to stomach.

"Rotting cadavers may not be the most glamorous research topic, but it is very important work that shouldn't be underestimated," he said.

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