Effects of bleach on carcass postmortem microbiomes and necrophagous beetle carcass attendance and their internal microbiomes.

Abstract

Forensic entomology, and potentially microbiology in the future, can be used during death investigations to corroborate an estimated time since death. Instances where products are introduced to a cadaver, either in attempt to conceal or by accident, can affect decomposition and succession of associated decomposer taxa (i.e., insects and bacteria). In this study, we tested the effect of two bleach (sodium hypochlorite) submersions on the outdoor decomposition and succession of carcass, soil, and beetle postmortem microbiomes using replicate (n = 5 per treatment) stillborn swine carcasses. Microbiomes from beetles, the carcasses, and the soil beneath them were sequenced from samples collected every two days. Beetle communities collected from pitfall traps were not significantly different between bleached and control carcasses through decomposition; however, there were fewer beetles collected from bleached carcasses until the last experimental day. Results from 16S rRNA amplicon sequencing revealed that microbiomes of carcasses and the soil beneath them did not significantly change when carcasses were bleached, and beetle internal microbiomes were not affected by the addition of bleach. Random forest modeling using soil microbiomes from underneath carcasses from both treatments was used to predict time since placement in the field with a 74.4% successful prediction rate, and modeling using beetle internal microbiomes predicted beetle family with 74.0% success. The introduction of bleach to the carcasses did not affect microbial or beetle communities, total decomposition time, or decrease accuracy of time of placement models.