Abstract
Bioconversion processes offer many economic, environmental, and societal advantages for production of fuels and chemicals. Successful commercialization of any biotechnology usually requires accurate characterization of cell growth dynamics, substrate conversion and production excretion rates. Despite recent advancements in analytical equipment, obtaining accurate measurement of gas component uptake or production rates remains challenging due to their high sensitivity to system pressure or volume changes. Specifically, the consumption and production of various gases will result in changes in system pressure (for batch operations) or off-gas flow rate (for continuous operations). These changes would cause significant errors in the estimated gas component uptake and production rates if they were not accounted for. In this work, we propose two easy-to-implement experimental protocols and associated calculation procedures to obtain accurate measurements of gas component consumption and production rates; one is for batch operation and one is for continuous operation. For depressurized (i.e., system pressure below 1 atm) batch cultures, nitrogen (or other inert gases) is used to repressurize the system to 1 atm before taking sample; while for continuous cultures, He (or other inert gases) is used as an internal tracer to accurately measure off-gas flow rate. The effectiveness and accuracy of the two protocols and associated calculation procedures are demonstrated using several case studies with both abiotic and biotic systems.
Highlights
Models (GEMs) as the cross membrane metabolic fluxes are commonly used constrains for GEMs development and refinement[2]
An example showing the detailed calculation procedure is provided in Supplementary Information S2
We propose two experimental protocols and associated calculation procedures to enable accurate measurements of gas component consumption and production rates in bioconversion processes
Summary
Models (GEMs) as the cross membrane metabolic fluxes are commonly used constrains for GEMs development and refinement[2]. The challenges with measuring gas component consumption and production rates are not caused by the precision of analytical equipment (e.g., gas chromatography) Instead, they are rooted in the fact that the consumption and/or production of gases alter the system headspace pressure (for batch processes) or gas phase flow rate (for continuous processes). They are rooted in the fact that the consumption and/or production of gases alter the system headspace pressure (for batch processes) or gas phase flow rate (for continuous processes) Such pressure or flow rate changes have not been explicitly or accurately accounted for in the available protocols for gas component measurements. For batch experiments that are conducted in closed-systems with constant volume such as vials, the system pressure often experiences significant reduction This can be caused by the overall gas consumption greater than gas production, as well as gas and/or liquid sampling. An aerobic methanotroph (Methylomicrobium buryatense 5GB1) serves as the model culture as it utilizes gaseous methane as the sole carbon and energy sources, consumes O2 and produces CO2 as a major product[4,7,8]
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