Bacteria and antibiotic resistance genes during carcass decomposition

Carcass decomposition in water may cause serious environmental pollution, which will pose a great threat to water quality and public health. However, water microbial community succession and antibiotic resistance genes (ARGs) during carcass decomposition process are less explored. Using high-throughput sequencing and high-throughput quantitative PCR techniques, the temporal succession of bacterial communities and ARGs profiles in experimental groups (fish carcasses) and control groups (no fish carcasses) containing two different types of water (the Yellow River water and tap water) from 3th to 19th day were studied. Our results showed that three parameters (pH, TOC and ORP) had linear correlations with decomposition time. Comamonas, Bacteroides and Pseudomonas significantly increased during carcass decomposition process. Alpha diversity (phylogenetic diversity and observed species (OTUs) indexes) of experimental groups was significantly lower than that in control groups. Time and treatment significantly influenced the bacterial community structures, and community dissimilarities between groups decreased over time, indicating that microbial community convergence. NH3-N, time and treatment were most important factors in determining bacteria community structures. The relative abundance of seven detected ARGs (cmlA1-01, floR, sul1, sul2, tetG-01, tetM-01 and tetQ) in the experimental groups were higher than those in the control groups. The ARGs concentrations in the experimental groups were even enriched 19-fold (minimum) to 148-fold (maximum) compared to tetQ of the Yellow River water in the control groups on 3th day. Redundancy analysis (RDA) indicated that two bacterial phyla (Firmicutes and Bacteroidetes) and environmental factors (NH3-N, ORP, CON, TDS and salinity) were significantly correlated with all detected ARGs. This study emphasizes that long-term input of nutrients causing by carcass decomposition in water firstly shifted the microbial community composition especially potential pathogens and then effected the ARGs profiles via microbial communities and environmental factors, thereby uncovering the harmful effects of related water pollution for human health.

水体中动物尸体腐败可引发严重环境污染，对水质及公众健康构成巨大威胁。然而，目前针对尸体腐败过程中水体微生物群落演替与抗生素抗性基因（antibiotic resistance genes，ARGs）的研究仍较为匮乏。本研究采用高通量测序与高通量定量PCR技术，针对两种水体（黄河水与自来水）中的实验组（添加鱼尸体）与对照组（无鱼尸体），于第3天至第19天期间的细菌群落时间演替规律与抗生素抗性基因谱特征展开分析。研究结果显示，pH、总有机碳（Total Organic Carbon，TOC）与氧化还原电位（Oxidation Reduction Potential，ORP）这三项参数与腐败时间呈线性相关。腐败过程中，丛毛单胞菌属（Comamonas）、拟杆菌属（Bacteroides）与假单胞菌属（Pseudomonas）的相对丰度显著升高。实验组的α多样性（包括系统发育多样性与观测物种数[OTUs]指数）显著低于对照组。采样时间与处理方式显著影响细菌群落结构，且组间群落相异度随时间推移逐渐降低，表明微生物群落存在趋同演替现象。氨氮（NH3-N）、采样时间与处理方式是决定细菌群落结构的最关键影响因子。实验组中7种检测到的抗生素抗性基因（cmlA1-01、floR、sul1、sul2、tetG-01、tetM-01与tetQ）的相对丰度均高于对照组。相较于对照组第3天黄河水中的tetQ基因，实验组的抗生素抗性基因浓度最高富集了148倍，最低也达到19倍。冗余分析（Redundancy Analysis，RDA）结果显示，两个细菌菌门——厚壁菌门（Firmicutes）与拟杆菌门（Bacteroidetes）——以及环境因子（氨氮[NH3-N]、氧化还原电位[ORP]、电导率[Conductivity，CON]、总溶解固体[Total Dissolved Solids，TDS]与盐度）与所有检测到的抗生素抗性基因均呈显著相关。本研究表明，水体中动物尸体腐败所引发的营养盐持续输入，首先会改变微生物群落组成（尤其是潜在致病菌），随后通过微生物群落与环境因子影响抗生素抗性基因谱特征，从而揭示了此类水体污染对人体健康的潜在危害。