Shaken not stirred - effect of different mixing modes during the cultivation of methanogenic pure cultures.

Numerous cultivation techniques for aerobic microorganisms have been extensively investigated in the field of microbiology. Optimisation of these techniques is important for scientific and economic reasons. Methanogenic archaea, however, are obligate anaerobic microorganisms requiring different cultivation techniques than aerobic organisms due to the fundamental differences in physiology. Mixing of aerobic cultures is generally considered as very important as it provides organisms with essential oxygen; however, for anaerobic microorganisms lacking the ability to grow with oxygen, this point in cultivation was widely neglected. This work aimed at investigating the effect of different mixing modes on cultures of the methanogenic archaea Methanomethylovorans thermophila, Methanosarcina acetivorans, Methanosarcina thermophila and Methanococcus vannielii by cultivating them anaerobically in the modes standing/lying, shaken/unshaken and large/small serum flask in order to analyse their impact on the methane and biomass production. This study showed that a shaken incubation mode had a positive impact on methane production and resulted in its accelerated production, especially in hydrogenotrophic cultures; however, higher methane production did not necessarily lead to higher biomass production.