In situ, High-Resolution Quantification of CO₂Uptake Rates via Automated Off-Gas Analysis Illuminates Carbon Uptake Dynamics in Cyanobacterial Cultures

Quantification of CO2 fixation rates by cyanobacteria is vital to determining their potential as industrial strains in a circular bioeconomy. Currently, however, CO2 fixation rates are most often determined through indirect and/or low-resolution methods, resulting in an incomplete picture of both dynamic behaviors and total carbon fixing potential. To address this, we developed a novel, low-cost system for in situ off-gas analysis which supports the automated acquisition of high-resolution and CO2 uptake rates from cyanobacterial cultures. Carbon fixation data obtained via this system was independently verified by elemental analysis of cultivated biomass. Using Synechococcus sp. PCC 7002 and Synechocystis sp. PCC 6803, we demonstrate that phototrophic CO2 uptake rates accelerate linearly to a maximum before then decaying monotonically to cessation by stationary phase. Furthermore, consistent with the expected stoichiometry, we found that strong correlations exist between both the rates and total levels of cell growth and carbon fixation. This system simultaneously provides a high-resolution growth curve, accurate carbon fixation rates, as well as the total amount of carbon fixed in a cyanobacterial batch culture, thus illuminating the parameters with which cyanobacterial researchers can exploit use to realize their full potential in industrial applications.