Soil bacterial and fungal succession during carrion decomposition in central South Africa: implications for microbial postmortem interval estimation

Background Accurate estimation of the postmortem interval remains a major challenge in forensic investigations, particularly during advanced decomposition when conventional methods become less reliable. Microbial succession has emerged as a promising supplementary approach for postmortem interval estimation; however, limited data are available from sub-Saharan African environments. This study investigated bacterial and fungal succession in gravesoil beneath decomposing pig carcasses in central South Africa using metabarcoding of the 16S ribosomal RNA and internal transcribed spacer gene regions. Three pig carcasses were monitored during autumn, and soil samples were collected across five decomposition stages: fresh, bloat, active decay, advanced decay, and dry/remains. Results Although decomposition rates differed among carcasses, consistent microbial succession patterns were observed throughout decomposition. Overall bacterial and fungal taxonomic richness declined in decomposition-affected soils compared with controls. Beta diversity analyses suggested clear stage-associated shifts in microbial community composition. Bacterial communities underwent substantial restructuring, with Firmicutes becoming increasingly dominant during later decomposition stages, particularly advanced decay and dry/remains. Fungal communities also exhibited distinct successional changes, with Ascomycota remaining the dominant phylum throughout decomposition. Marked microbial transitions were associated with carcass rupture and the release of decomposition fluids, which altered the soil environment and promoted the emergence of decomposition-associated taxa. Several microbial taxa previously reported as decomposition indicators were identified, together with taxa that may be characteristic of the regional environment. Conclusions The findings demonstrate that decomposition-associated bacterial and fungal succession patterns are detectable under central South African environmental conditions and remain discernible despite biological variability among carcasses. Distinct microbial shifts occurred across decomposition stages, particularly during advanced decomposition, supporting the potential forensic value of microbial metabarcoding as a supplementary approach for postmortem interval estimation. This study provides important baseline data on gravesoil microbial succession in South Africa and contributes to the development of region-specific microbial reference frameworks for forensic applications.