Aims Microbial consortia can be more efficient at biological processes than single isolates. The purposes of this study were to design and evaluate a synthetic microbial consortium containing the methanotroph Methylocystis sp. M6 and the helper Hyphomicrobium sp. NM3, and develop a novel methanotrophic process for this consortium utilizing a dialysis membrane. Methods and Results Hyphomicrobium increased the methane-oxidation rate (MOR), biomass and stability at a dilution rate of 0.067 day(-1) in fed-batch co-culture. qRT-PCR showed that Methylocystis population increased gradually with time, whereas Hyphomicrobium population remained stable despite cell washing, confirming synergistic population interaction. At 0.1 day(-1), spiking of Hyphomicrobium effectively increased the methanotrophic activity, after which Hyphomicrobium population decreased with time, indicating that the consortium is optimal at Hyphomicrobium was grown in dialysis membrane within the bioreactor, MOR increased linearly up to 155.1 +/- 1.0 mmol l(-1) day(-1) at 0.067, 0.1, 0.2 and 0.4 day(-1), which is the highest observed value for a methanotrophic reactor. Conclusions Hyphomicrobium sp. NM3 is a promising helper micro-organism for methanotrophs. Hyphomicrobium-methanotroph consortia used concurrently with existing methods can produce an efficient and stable methane oxidation system. Significance and Impact of the Study This novel methanotrophic process is superior to those previously reported in the literature, and can provide efficient and stable methane oxidation.