To effectively mitigate global warming and climate change, society must develop new science and technologies for transitioning from a fossil carbon-based to a CO2-based economy. CO2 captured from point sources or directly from the air can be utilized as a feedstock in CO2 reduction to make carbon-based products using renewable electricity. Significant amounts of renewable electricity, generated by wind, solar, or hydropower, is becoming available at costs cheaper than fossil-based electricity, allowing for fossil-fuel independent, economically viable-electrification of fuel production and chemical syntheses. To achieve effective CO2 conversion, metabolism of methanogenic archaea and acetogenic bacteria provides a unique opportunity to convert CO2 into useful fuels and chemical precursors with high selectivity at ambient conditions, thus, eliminating the need for high energy-dependent chemical and separation processes. For example, by feeding H2 generated by electrolysis via renewable electricity and combining with CO2 recycled from sources such as anaerobic digestors, landfill, and fermentation facilities, microbes can synthesize valuable products such as methane (by methanogenesis) or acetate (by acetogenesis). Such biocatalytic processes represent promising solutions to produce carbon-neutral commodity chemicals and fuels from CO2, in particular of compounds that are amenable for long-term energy storage for intermittent renewable energy sources (CH4). To promote the application of methanogen, in this seminar, I will describe how substrate flux (i.e., feed inflow) affects the physiology - metabolic activity, biomass synthesis and composition - of methanogens using a quantitative and systemic biology approach. In addition, I will present preliminary results of how intermittent starvation affects the activity of methanogens.