Cell disruption by cationic surfactants affects bioproduct recovery from Synechocystis sp PCC 6803

Cationic surfactants can be used to improve extraction of high-value products from microalgae, but the best way to apply cationic surfactants has not been established. We evaluated the impacts of contact time and concentration for two cationic surfactants - dodecyltrimethylammonium bromide (DTAB) and hexadecyl-trimethylammonium bromide (CTAB) - on extraction of lipids and nonpolar pigments, carotenoids and chlorophyll a, from Synechocystis sp. PCC 6803. For the most dose-effective concentration, pigment extraction was better with the longer alkyl-chain length, i.e., CTAB > DTAB, because the longer alkyl chain of CTAB increased cell membrane permeability, causing cell lysis that allowed solvent-pigment contact. A CTAB dose of 25 mM and treatment for 5 h gave the highest pigment extraction, nearly 30 and 12 mg/g dried biomass for chlorophyll a and carotenoids, respectively. In contrast, lipid recovery was better with the shorter alkyl-chain length, DTAB > CTAB. DTAB disrupted the cells less, which allowed the solvent to access more lipids held in the cells. Thus, the selection of surfactant and dosing strategy depends on which products are targeted. With moderate cell disruption, a moderate dose of CTAB (10 mM) was effective for recovering pigments and lipids simultaneously.