唾液是犯罪现场常见的生物检验材料,在法医学案件调查中具有较高的应用价值。能够反映犯罪嫌疑人在现场的作案时间,为犯罪嫌疑人的犯罪事实提供证据。尽管许多研究人员已经提出了他们的实验方案来估计自唾液沉积(TsD)以来的时间,关于使用微生物来估计TsD的研究仍然相对缺乏。在目前的研究中,探讨了不同TsD值唾液中微生物群落的演替变化,以识别与唾液TsD相关的微生物标志物。我们收集了住在贵州的六个无关的健康汉族个体的唾液样本,在6个时间点(0、1、3、7、15和28天)将这些样品暴露于室内条件。通过16SrRNA测序(V3-V4区域)研究了这些样品中微生物组成的时间变化。通过评估属水平上微生物丰度的时间变化模式,四种细菌(布鲁氏菌,普雷沃氏菌,假单胞菌,和梭杆菌)在这些样品中观察到显示出良好的时间依赖性。此外,分层聚类和主坐标分析结果显示,这些唾液样本可分为t短(≤7天)和t长(>7天)组.最后,建立了随机森林模型来预测这些样本的TsD。对于模型,均方根误差,预测和实际TsD值之间的R2和平均绝对误差分别为1.5213、0.9851和1.1969。总而言之,我们在唾液样本中鉴定了TsD相关的微生物标记,这可以被视为推断唾液TsD的有价值的标志物。
Saliva is a common biological examination material at crime scenes and has high application value in forensic case investigations. It can reflect the suspect\'s time of crime at the scene and provide evidence of the suspect\'s criminal facts. Even though many researchers have proposed their experimental protocols for estimating the time since deposition (TsD) of saliva, there is still a relative lack of research on the use of microorganisms to estimate TsD. In the current study, the succession change of microbial community in saliva with different TsD values was explored to discern the microbial markers related to TsD of saliva. We gathered saliva samples from six unrelated healthy Han individuals living in Guizhou, China and exposed these samples to indoor conditions at six time points (0, 1, 3, 7, 15, and 28 days). Temporal changes of microbial compositions in these samples were investigated by 16S rRNA sequencing (V3-V4 regions). By assessing temporal variation patterns of microbial abundance at the genus level, four bacteria (Brucella, Prevotella, Pseudomonas, and Fusobacterium) were observed to show good time dependence in these samples. In addition, the hierarchical clustering and principal co-ordinates analysis results revealed that these saliva samples could be classified into t-short (≤7 days) and t-long (>7 days) groups. In the end, the random forest model was developed to predict the TsD of these samples. For the model, the root mean square error, R2, and mean absolute error between predicted and actual TsD values were 1.5213, 0.9851, and 1.1969, respectively. To sum up, we identified TsD-related microbial markers in saliva samples, which could be viewed as valuable markers for inferring the TsD of saliva.