Evaluations and comparisons of microbial diversities in four types of body fluids based on two 16S rRNA gene...

Body fluids are one of the common biological traces at crime scenes. Understanding the types of these biological traces could provide key clues for the investigations of the forensic cases. In recent years, partial hypervariable regions of 16S rRNA gene sequencing and full-length 16S rRNA gene sequencing have attracted the interests of researchers and we intend to explore which method can be better applied to forensic researches.

In this study, the 16S rRNA gene V3-V4 (short-read) sequencing based on next-generation sequencing and the full-length 16S rRNA gene sequencing based on single molecule real-time sequencing were used to classify microbes in saliva, peripheral blood, vaginal secretion and menstrual blood samples.

Alpha diversity metrics in short-read sequencing were larger than those of full-length sequencing. Phylum-level bacteria in four kinds of body fluids obtained from the two platforms were similar, while their abundances were different. The results of principal coordinates analysis and analysis of molecular variance indicated the microbial compositions of vaginal secretion and menstrual blood samples were similar, and the microbial compositions among saliva, peripheral blood, vaginal secretion or menstrual blood samples were significantly different. The linear discriminant analysis effect size showed the differential bacteria screened among the four kinds of body fluids were variant in two sequencing results.

Both sequencing methods could be used to detect bacterial diversities in four different types of body fluids and provide potential tools for microbes to identify the four kinds of body fluids in forensic investigation, in which full-length sequencing could provide more accurate taxonomy.