In Situ, High-Resolution Quantification of CO₂ Uptake Rates via Automated Off-Gas Analysis Illuminates Carbon Uptake Dynamics in Cyanobacterial Cultures

Quantification of cyanobacterial CO₂ fixation rates 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 fixation potential. To address this, we developed the "Automated Carbon and CO₂ Experimental Sampling System" (ACCESS); a low-cost system for in situ off-gas analysis that supports the automated acquisition of high-resolution volumetric CO₂ uptake rates from multiple cyanobacterial cultures in parallel. Carbon fixation data obtained via ACCESS were first independently validated by elemental analysis of cultivated biomass. Using ACCESS, we then demonstrate how the volumetric CO₂ uptake rate of two model cyanobacteria, Synechococcus sp. PCC 7002 and Synechocystis sp. PCC 6803, accelerates linearly to a maximum before then decaying monotonically to cessation by stationary phase. Furthermore, consistent with the expected stoichiometry, strong correlations were also found to exist between cell growth and carbon fixation, both in terms of rates as well as total levels. The novel insights made possible via ACCESS will aid other cyanobacterial researchers in diverse fundamental and applied research efforts.