Quantitative analysis of methane monooxygenase (MMO) explains process robustness in continuous and feast-famine bioreactors treating methane

Abstract

The ability of methanotrophs to rapidly respond to intentional or accidental stress conditions caused by operational failures or process fluctuations is of utmost importance to guarantee the robustness of CH4 abatement biotechnologies. In this study, the performance of a continuous and two feast-famine (5:5 days feast-famine cycles) stirred tank reactors treating diluted CH4 emissions (4–5% v/v) was comparatively assessed for 149 days. The robustness of the three bioreactors towards a 5 days CH4 deprivation episode was thoroughly evaluated at a molecular level (pmoA gene expression level) and correlated to macroscopic process performance. The bioreactors recovered their steady-state abatement performance (in terms of CH4 elimination capacity and CO2 production rate) within 1.5–2 h following CH4 supply resumption concomitantly with a maximum in pmoA gene expression, regardless of the previous operational mode. However, while methanotrophs from the continuous unit maintained higher basal levels of pmoA expression as a strategy for a rapid CH4 metabolism initiation, the strategy of the feast-famine adapted-methanotrophs consisted on a more accurate regulation of their pmoA transcripts levels along with a higher and/or more rapid induction of the pmoA gene by CH4 availability.