Effect of culture conditions at lab-scale on metabolite composition and antibacterial and antibiofilm activities of Dunaliella tertiolecta

Dunaliella tertiolecta RCC6 was cultivated indoors in glass bubble column photobioreactors operated under batch and semi-continuous regimens and using two different conditions of light and temperature. Biomass was harvested by centrifugation, frozen, and then lyophilized. The soluble material was obtained by sequential extraction of the lyophilized biomass with solvents with a gradient of polarity (hexane, ethyl acetate, and methanol) and its metabolic composition was investigated through nuclear magnetic resonance (NMR) spectroscopy. The effect of light on chlorophyll biosynthesis was clearly shown through the relative intensities of the H-1 NMR signals due to pheophytins. The highest signal intensity was observed for the biomasses obtained at lower light intensity, resulting in a lower light availability per cell. Under high temperature and light conditions, the H-1 NMR spectra of the hexane extracts showed an incipient accumulation of triacylglycerols. In these conditions and under semi-continuous regimen, an enhancement of beta-carotene and sterols production was observed. The antibacterial and antibiofilm activities of the extracts were also tested. Antibacterial activity was not detected, regardless of culture conditions. In contrast, the minimal biofilm inhibitory concentrations (MBICs) against Escherichia coli for the hexane extract obtained under semi-continuous regimen using high temperature and irradiance conditions was promising.

Automated summary

The metabolic composition of Dunaliella tertiolecta RCC6 was investigated through NMR spectroscopy by cultivating it under different light and temperature conditions and extracting the active ingredients. The results showed that light had a clear effect on chlorophyll biosynthesis, with higher chlorophyll content obtained under lower light intensity. Under high temperature and light conditions, there was an accumulation of triacylglycerols in the hexane extracts. Furthermore, the hexane extract obtained under high temperature and irradiance conditions in the semi-continuous regimen showed promising minimal biofilm inhibitory concentrations (MBICs) against Escherichia coli.