Investigation of diverse bacterial communities in the leachate from pig decomposition by using high-throughput sequencing

The leachate generated by the decomposition of animal carcass has been implicated as an environmental contaminant around the burial site. The organic degradation of carcass by environmental factors including microbes generates a leachate, and this product may affect the other soil microorganisms and environmental characters. Therefore, this study was conducted to investigate the microbial communities in leachate originated from pig carcass decomposition by using high-throughput sequencing. The leachate samples were collected once per week during 98 days, and the microbial communities in the leachate were investigated for 14 weeks by 16S rRNA gene analysis. A total of 51,230 reads were obtained from extracted DNA of 6 different samples (1, 2, 3, 4, 6 and 14 weeks), phylum of Firmicutes was predominated induring sampling periods. The diversity of bacterial community in leachate was the highest at 6 weeks, whereas the diversity of communities in 2 weeks and 14 weeks were lower than other samples. The relative abundance of Firmicutes was reduced, while the proportions of Bacteroidetes and Proteobacteria were increased from 3 weeks to 6 weeks. The composition of community was seem to be returned after 14 weeks at phylum level, however, the difference of community structure between the samples of 14 weeks and early stage (1-2 weeks) could be investigated clearly at family, genus and species level. The pH of lechate could be related to the shift of microbial community. Most of the bacteria were anaerobic bacteria belonging to the families of Tissierella, Clostridiales and Peptostreptococcus. The genus of Peptostreptococcus was increased at 14 weeks sample, uncultured Tissierella was increased from 2 weeks to 4 weeks samples. The changes of bacterial community were also investigated by PCoA plots using UniFrac distance and community similarity analysis. These results indicated that the bacterial communities in leachate generated from pig decomposition were continuously shifted during the period of decomposition and this change could be influenced to burial sites.

动物尸体腐败过程中产生的渗滤液，已被证实为墓葬遗址周边的一类环境污染物。在包括微生物在内的各类环境因子作用下，尸体发生有机降解并产生渗滤液，该产物可对其他土壤微生物及环境特征造成影响。因此，本研究采用高通量测序（high-throughput sequencing）技术，对猪尸体腐败产生的渗滤液内的微生物群落展开探究。本研究在98天的周期内每周采集一次渗滤液样本，并通过16S rRNA基因（16S ribosomal RNA gene）分析，对覆盖14周时长的渗滤液微生物群落进行研究；最终从1、2、3、4、6及14周共6个不同样本的提取DNA中，获得了总计51230条测序读段（reads）。在整个采样周期内，厚壁菌门（Firmicutes）始终为优势菌群。渗滤液中细菌群落的多样性在6周时达到峰值，而2周和14周样本的群落多样性低于其余采样样本。从3周过渡至6周期间，厚壁菌门的相对丰度逐渐降低，拟杆菌门（Bacteroidetes）与变形菌门（Proteobacteria）的占比则逐步升高。在门分类水平上，14周样本的群落组成似乎恢复至初始状态；但在科、属、种分类水平上，14周样本与早期样本（1-2周）的群落结构差异仍可被清晰辨识。渗滤液的pH值可能与微生物群落的演替存在关联。绝大多数检出的细菌为厌氧细菌，分属于蒂瑟菌属（Tissierella）、梭菌目（Clostridiales）及消化链球菌属（Peptostreptococcus）。其中，消化链球菌属在14周样本中的丰度显著提升，未培养的蒂瑟菌属则在2周至4周的样本中丰度逐步上升。本研究还通过基于UniFrac距离的主坐标分析（PCoA）图及群落相似性分析，对细菌群落的动态变化进行了探究。上述结果表明，猪尸体腐败产生的渗滤液内的细菌群落随腐败进程持续发生演替，且该演替过程可对墓葬遗址造成影响。