A Portable Anaerobic Microbioreactor Reveals Optimum Growth Conditions for the Methanogen Methanosaeta concilii

ABSTRACT Conventional studies of the optimum growth conditions for methanogens (methane-producing, obligate anaerobic archaea) are typically conducted with serum bottles or bioreactors. The use of microfluidics to culture methanogens allows direct microscopic observations of the time-integrated response of growth. Here, we developed a microbioreactor (μBR) with ∼1-μl microchannels to study some optimum growth conditions for the methanogen Methanosaeta concilii. The μBR is contained in an anaerobic chamber specifically designed to place it directly onto an inverted light microscope stage while maintaining a N2-CO2 environment. The methanogen was cultured for months inside microchannels of different widths. Channel width was manipulated to create various fluid velocities, allowing the direct study of the behavior and responses of M. concilii to various shear stresses and revealing an optimum shear level of ∼20 to 35 μPa. Gradients in a single microchannel were then used to find an optimum pH level of 7.6 and an optimum total NH4-N concentration of less than 1,100 mg/liter (<47 mg/liter as free NH3-N) for M. concilii under conditions of the previously determined ideal shear stress and pH and at a temperature of 35°C.

Carbon Isotope Fractionation during Acetoclastic Methanogenesis by Methanosaeta concilii in Culture and a Lake Sediment

ABSTRACT The isotope enrichment factors (ε) in Methanosaeta concilii and in a lake sediment, where acetate was consumed only by Methanosaeta spp., were clearly less negative than the ε usually observed for Methanosarcina spp. The fraction of methane produced from acetate in the sediment, as determined by using stable isotope signatures, was 10 to 15% lower when the appropriate ε of Methanosaeta spp. was used.