Microalgae is promising source of biofuel and high value chemicals. The major limitation for large scale algal production is to cultivate microalgae at low biomass density, which impacts its economic feasibility at industrial scale. Locally isolated microalgal strain Cyanobacterium aponinum CCC734 was tested for mass cultivation. Nitrogen and phosphorus in the ratio of 12:1 was optimized for maintaining sustained algal biomass productivity. The molecular characterization of growth as a function of the exometabolite dynamics has been poorly characterized component of algal growth. To understand density associated cultivation bottlenecks, secretome dynamics were monitored at biomass densities from 0.6±0.1 to 7±0.1 g/L (2 to 22 OD) in batch mode. Liquid chromatography coupled with mass spectrometry, identified 880 exometabolites in the supernatant of C. aponinum CCC734. A statistical analysis by PCA biplot and clustering showed similarity between exometabolite profiles at low (1.2±0.2 and 2.5±0.2 g/L) and mid biomass (3.8±0.2 and 5±0.5 g/L), whereas high biomass concentration (6.5±0.2 and 7±0.1 g/L) was distinctly separate. Sets of exometabolites were identified based on their role in influencing growth and relative mass signal intensity. Taking cues from exometabolite dynamics, 5±0.5 g/L biomass concentration (16 OD) was found optimal for C. aponinum CCC734 cultivation and continuous operation was demonstrated in semi-turbidostat mode. Secretomics based monitoring tool proposed in this manuscript is first comprehensive growth studies of exometabolite accumulation at the molecular level at variable biomass densities. This tool could be utilized in analyzing and directing algal cultivation strategies at high density and reduction in overall operation cost.
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