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Two different quantitative PCR platforms, droplet digital PCR (dd-PCR) and quantitative real-time PCR (qPCR), were compared in a mcrA-based methanogen community assay that quantifies ten methanogen sub-groups. Both technologies exhibited similar PCR efficiencies over at least four orders of magnitude and the same lower limits of detection (8 copies μL-DNA extract−1). The mcrA-based methanogen communities in three full-scale anaerobic digesters were examined using the two technologies. dd-PCR detected seven groups from the digesters, while qPCR did five groups, indicating that dd-PCR is more sensitive for DNA quantification. Linear regression showed quantitative agreements between both of the technologies (R2 = 0.59–0.98) in the five groups that were concurrently detected. Principal component analysis from the two datasets consistently indicated a substantial difference in the community composition among the digesters and revealed similar levels of differentiation among the communities. The combined results suggest that dd-PCR is more promising for examining methanogenic archaeal communities in biotechnological processes.

Methanotrophs are a biological resource as they degrade the greenhouse gas methane and various organic contaminants. Several non-methanotrophic bacteria have shown potential to stimulate growth of methanotrophs when co-cultured, and however, the ecology is largely unknown. Effects of Sphingopyxis sp. NM1 on methanotrophic activity and growth of Methylocystis sp. M6 were investigated in this study. M6 and NM1 were mixed at mixing ratios of 9:1, 1:1, and 1:9 (v/v), using cell suspensions of 7.5 × 1011 cells L−1. Methane oxidation of M6 was monitored, and M6 population was estimated using fluorescence in situ hybridization (FISH). Real-time PCR was applied to quantify rRNA and expression of transcripts for three enzymes involved in the methane oxidation pathway. NM1 had a positive effect on M6 growth at a 1:9 ratio (p

The depth profiles of the CH4 oxidation potentials and the methanotrophic community were characterized in a lab-scale soil mixture biocover. The soil mixture samples were collected from the top (0-10 cm), middle (10-40 cm), and bottom (40-50 cm) layers of the biocover where most of methane was oxidized at the top layer due to consumption of O2. Batch tests using serum bottles showed that the middle and bottom samples displayed CH4 oxidation activity under aerobic conditions, and their CH4 oxidation rates were 85 and 71% of the rate of top sample (8.40 μmol g dry sample-1 h-1), respectively. The numbers of methanotrophs in the middle and bottom were not significantly different from those in the top sample. There was no statistical difference in the community stability indices (diversity and evenness) among the methanotrophic communities of the three layer samples, even though the community structures were distinguished from each other. Based on microarray analysis, type I and type II methanotrophs were equally present in the top sample, while type I was more dominant than type II in the middle and bottom samples. We suggested that the qualitative difference in the community structures was probably caused by the difference in the depth profiles of the CH4 and O2 concentrations. The results for the CH4 oxidation potential, methanotrophic biomass, and community stability indices in the middle and bottom layer samples indicated that the deeper layer in the methanotrophic biocover serves as a bioresource reservoir for sustainable CH4 mitigation. [ABSTRACT FROM AUTHOR]