Bacterial community dynamics in a long-term operated soil biocover packed with an engineered soil. biofilm metagenome

An engineered soil (a mixture of tobermolite, landfill soil and earthworm cast) was developed as a bed material for methane-removal biocover. In order to evaluate the engineered soil, methane-oxidizing performance and bacterial community were monitored for 134 days. There were three different stages: methane only (stage 1, 39 days), methane with trimethylamine (TMA) (stage 2, 65 days) and methane with TMA and dimethyl sulfide (DMS) (stage 3, 29 days). The methane removal efficiencies were 59.8?9.4 % (elimination capacity: 220.4?34.5 g CH4•m-2•d-1), 74.2?4.2 % (273.6?15.4 g CH4•m-2•d-1) and 70.7?2.5 % (260.9?9.3 g CH4•m-2•d-1) in the stages 1, 2 and 3, respectively. Depth profiles of gases indicated that methane was stably oxidized at the top layer (0-10 cm), while TMA and DMS were completely removed at the bottom layer (40-50 cm). Quantitative PCR indicated that bacterial populations did not differ among stages at each layer. Ribosomal tag pyrosequencing showed that Methylocaldum was most abundant at the top layer in all stages, while Pseudoxanthomonas, Methylocaldum and methylobacter were dominant at the stages 1, 2 and 3, respectively at the bottom layer. Principal component analysis and Mantel test revealed that both total bacterial and methanotrophic community compositions were highly conserved among stages at the top layer, while substantially varied at the bottom layer due to the added volatile organic compounds. These results indicated that the performance of biocover remained stable owing to the community stability at the top layer. Therefore, the stability of methane-oxidizing performance and microbial community suggests that the engineered soil is promising as a bed material for methane removal as well as volatile organic compounds.