Arsenic (As) is a potential contaminant in sewage sludge that may affect waste treatment and limit the use of these waste materials as soil amendments. Anaerobic digestion (AD) is an important and effective process for the treatment of sewage sludge and the chemical speciation of As is particularly important in sludge AD. However, the biotransformation genes of As in sludge during AD has not been fully explored. In this study, the influent and effluent sludge of anaerobic digester in a wastewater treatment plant (WWTP) was collected to investigate the species transformations of As, the abundance and diversity of As biotransformation genes was explored by real-time PCR (qPCR) and metagenomic sequencing, separately. The results showed that arsenite [As(III)] and arsenate [As(V)] were predominant in the influent sludge, whereas the relative abundance of monomethylarsenic acid (MMA) increased by 25.7% after digestion. As biotransformation genes were highly abundant, and the As(III) S-adenosylmethionine methyltransferase (arsM) gene was the predominant which significantly increased after AD by qPCR analysis. Metagenomic analysis indicated that the diversity of the arsM-like sequences also increased significantly after AD. Most of the arsM-like sequences in all the influent and effluent sludge samples were related to Bacteroidetes and Alphaproteobacteria. Furthermore, co-occurrence network analysis indicated a strong correlation between the microbial communities and As. This study provides a direct and reliable reference on As biotransformation genes and microbial community in the AD of sludge.

砷（As）是污水污泥中的潜在污染物，可能会影响废物处理并限制这些废物作为土壤改良剂的使用。厌氧消化（AD）是处理污水污泥的重要而有效的过程，As的化学形态在污泥AD中尤其重要。然而，AD中污泥中As的生物转化基因尚未得到充分研究。本研究收集废水处理厂厌氧消化池的进水和出水污泥，以研究As的物种转化，并通过实时PCR（qPCR）和宏基因组学探索As生物转化基因的丰度和多样性分别进行排序。结果表明，进水污泥中砷[As（III）]和砷酸盐[As（V）]占主导地位，消化后，单甲基砷酸（MMA）的相对丰度增加了25.7％。由于生物转化基因非常丰富，As（III）S-腺苷甲硫氨酸甲基转移酶（通过qPCR分析，AD后显着增加了arsM）基因。元基因组学分析表明，在AD后，类似arsM的序列的多样性也显着增加。所有进水和出水污泥样品中的大多数arsM样序列都与拟杆菌和Alphaproteobacteria有关。此外，共现网络分析表明微生物群落与砷之间有很强的相关性。该研究为污泥AD中As的生物转化基因和微生物群落提供了直接可靠的参考。