Microbial respiration rates in soils below decomposing cadavers.

<p>Means and standard deviations of n = 4 cadavers are presented for each stage; means with the same letter are not significantly different (p < 0.05, mixed model ranked ANOVA, Tukey-Kramer post-hoc). The light grey bar is the mean and standard deviation for control (no cadaver) soils throughout the duration of the study (n = 45).</p

Abundance of human-associated <i>Bacteroides</i> in soils below decomposing cadavers.

<p>Mean and standard deviation (n = 3 cadavers) abundances for each decomposition stage; means with the same letter are not significantly different (p < 0.05, mixed model ANOVA, Tukey-Kramer post-hoc).</p

Soil pH and chemical concentrations in soils below decomposing cadavers.

<p>TN and TOC are total extractable nitrogen and organic carbon, respectively. Each number is the mean ± standard deviation of n = 4 cadavers. Statistically, stages that were significantly different from the others are indicated by different letter designation (p < 0.05, ranked ANOVA, Tukey-Kramer).</p><p>Soil pH and chemical concentrations in soils below decomposing cadavers.</p

Human-associated bacterial OTUs detected in soils below decomposing cadavers.

<p>Mean relative abundances (n = 4) by decomposition stage. These OTUs were selected because they were present at > 0.05% in gut communities < 0.02% in the initial and control soils and > 0.02% in soils below cadavers during decomposition. <i>uc</i> = unclassifiable with at least 80% confidence using the RDP classifier.</p

Richness and diversity of soil microbial communities below decomposing cadavers.

<p>A. Chao1 richness estimate, and B. Inverse of the Simpson diversity index, both calculated on libraries of equal size (121,340 sequences). Gut samples were also included for comparison. Mean and standard deviation of n = 4 cadavers are presented for each stage; means with the same letter are not significantly different (p < 0.05, mixed model ANOVA, Tukey-Kramer post-hoc). The light grey bar is the mean and standard deviation of the control (no cadaver) soil libraries throughout the duration of the study (n = 8).</p

Functional and Structural Succession of Soil Microbial Communities below Decomposing Human Cadavers

<div><p>The ecological succession of microbes during cadaver decomposition has garnered interest in both basic and applied research contexts (e.g. community assembly and dynamics; forensic indicator of time since death). Yet current understanding of microbial ecology during decomposition is almost entirely based on plant litter. We know very little about microbes recycling carcass-derived organic matter despite the unique decomposition processes. Our objective was to quantify the taxonomic and functional succession of microbial populations in soils below decomposing cadavers, testing the hypotheses that a) periods of increased activity during decomposition are associated with particular taxa; and b) human-associated taxa are introduced to soils, but do not persist outside their host. We collected soils from beneath four cadavers throughout decomposition, and analyzed soil chemistry, microbial activity and bacterial community structure. As expected, decomposition resulted in pulses of soil C and nutrients (particularly ammonia) and stimulated microbial activity. There was no change in total bacterial abundances, however we observed distinct changes in both function and community composition. During active decay (7 - 12 days postmortem), respiration and biomass production rates were high: the community was dominated by Proteobacteria (increased from 15.0 to 26.1% relative abundance) and Firmicutes (increased from 1.0 to 29.0%), with reduced Acidobacteria abundances (decreased from 30.4 to 9.8%). Once decay rates slowed (10 - 23 d postmortem), respiration was elevated, but biomass production rates dropped dramatically; this community with low growth efficiency was dominated by Firmicutes (increased to 50.9%) and other anaerobic taxa. Human-associated bacteria, including the obligately anaerobic <i>Bacteroides</i>, were detected at high concentrations in soil throughout decomposition, up to 198 d postmortem. Our results revealed the pattern of functional and compositional succession in soil microbial communities during decomposition of human-derived organic matter, provided insight into decomposition processes, and identified putative predictor populations for time since death estimation.</p></div

Bacterial phyla in soils below cadavers at different stages of decomposition.

<p>The data are the mean relative abundances of the 12 most abundance phyla from four cadavers.</p

Microbial community structure in soils below decomposing cadavers.

<p>A. NMDS ordination of Bray Curtis dissimilarities between the relative abundance of bacterial OTUs. Shapes denote the 4 cadavers: A3 (square), B4 (diamond), C5 (hex), D6 (circle). Crossed symbols are control (no cadaver) samples. B. Second stage NMDS comparing the stages of decomposition, with arrows denoting order of stages through time.</p

Bacterial OTUs that significantly change between stages of decomposition.

<p>Mean relative abundances (n = 4) of OTUs that are significantly different between stages (p < 0.05, ANOVA, Tukey-Kramer post-hoc). Only OTUs with more than 0.001% mean relative abundance in at least one stage and an effect size of 0.50 or larger are included here.</p