Optimization of the cultivation conditions for Synechococcus sp. PCC7942 (cyanobacterium) to be used as feedstock for biodiesel production

Abstract

Cyanobacteria have several advantages as lipid feedstock for biodiesel production compared to microalgae. These benefits include the ability to increase lipid content via genetic manipulation, a high growth rate, nitrogen-fixation and a simpler cell wall, which aids in lipid extraction. Moreover, these bacteria have the capability to convert solar energy into biomass that is two times greater than microalgae and ten times greater than corn and sugar cane. The aim of this study was to optimize the cultivation conditions of Synechococcus sp. PCC7942 and to evaluate the lipid feedstock to generate biodiesel via an enzymatic route. For this purpose, the effect of light intensity (50–150μmolm−2s−1) and the concentration of Na2CO3 (0.5–1.5gL−1) were studied according to a 22 full-factorial design. Under optimized conditions, the biomass productivity (QP) of 124.0±3.2mgL−1day−1, lipid content of 29.0±2.1% and lipid productivity of 35.9±0.5mgL−1day−1 were obtained. The fatty acid profile indicated differences when the medium was enriched with Na2CO3 and cultured in high light intensity, resulting in an increase in unsaturated fatty acids, particularly linoleic acid, which accounts for 40% of the fatty acids in Synechococcus sp. PCC7942. The lipid feedstock was characterized and used as feedstock for biodiesel synthesis using Novozym® 435 as a catalyst and ethanol as an acyl acceptor. The biocatalyst was able to form ethyl esters from all of the fatty acids present in the lipid feedstock, attaining a conversion of 97.1%. Analysis of Synechococcus sp. PCC7942 lipids indicated the potential of this cyanobacterium as a biodiesel feedstock. The primary fatty acids of this cyanobacterium were C16–C18, which is suitable for the production of good-quality biodiesel.