A method to compute instantaneous oxygen evolution rates in cyanobacterial cultures grown in shake flasks

Cyanobacteria have been attracting attention for various biotechnological applications due to their ability to carry out oxygenic photosynthesis. The oxygen evolution rate (OER) of cyanobacterial cultures is a key physiological parameter, which is typically measured offline by using oxygen electrodes. In situ measurement of OER has been reported in a photobioreactor fitted with a dissolved oxygen (DO) probe. Here, we show that the OER can be estimated from online measurements of the DO levels by using sensors fitted in shake flasks, which are widely used for preliminary characterization of microbial strains. We study how the DO levels change under diurnal light regime and different growth conditions in two strains of Synechococcus elongatus, namely, PCC 7942 and PCC 11801, in shake flasks. We use the DO levels coupled with the knowledge of the overall gas-liquid mass transfer coefficient for oxygen (k(L)a) to compute the OER. For the growth conditions tested, the cumulative oxygen evolved in a day correlated with the increase in biomass suggesting that the calculated OER, in turn, might provide an estimate of the organism's growth rate. We believe that the method may be widely applicable for the growth characterization of organisms that perform oxygenic photosynthesis.