Utilization of blue light-emitting diodes in Ensifer meliloti cultivation for enhanced production of antioxidant biopolymers

Abstract

In this work, we present a pioneering study about the application of blue light-emitting diodes (LED) in the submerged cultivation of the diazotrophic bacterium Ensifer meliloti SEMIA 135. We hypothesize that applying blue light can modify the physiological parameters of cultivation, increasing extracellular polymeric substances (EPS) production and improving its antioxidant activity. Firstly, blue LED was applied during all 96 h of cultivation, which promoted higher biomass concentration and specific growth rates than the one without illumination. However, a clear influence of blue light intensity was not observed in the production of polymeric substances. A novel strategy was proposed, consisting of the application of blue LED only up to the first 24 h of cultivation (exponential phase). In such conditions, cultures exposed to 50 μmol m⁻² s⁻¹ showed a maximum EPS production (4.79 g L⁻¹) at 72 h, while the control without illumination showed 3.17 g L⁻¹ at 96 h. Finally, the effects of the EPS produced through cultivation under blue LED incidence were evaluated regarding antioxidant activity by capturing DPPH^• and ABTS^• radicals and reducing power. A dose-dependent behavior was observed for all antioxidant assays performed. However, only DPPH^• radical antioxidant assay showed a positive influence when blue LED at 50 μmol m⁻² s⁻¹ was applied. These results showed that cultivation associated with blue LED could improve EPS synthesis and their antioxidant activity. The results expand the opportunities for EPS applications as a thickener, stabilizer, emulsifier, or antioxidant agent and demonstrate the advantages of high productivity associated with an eco-friendly approach.