Evaluation of disruption/permeabilization methodologies for Microcystis aeruginosa as alternatives to obtain high yields of microcystin release

Abstract

The extraction of the wide range of useful bioactive compounds produced by cyanobacteria is still a major bottleneck at industrial scale. In addition to the high costs, extraction efficiencies are also commonly low, with low cell disruption efficiencies playing a particularly significant role in intracellular compounds' release. To increase the chances of an extended use of the cyanobacteria toxin microcystin in several biotechnological fields, we aimed to optimize five different disruption techniques: bead milling, microwave, freeze-thaw cycles, high-speed homogenization, and sonication. For each of the methods tested, the conditions that maximized the intracellular organic matter release were: i) 20% of beads and treatment time of 7 min (bead milling); ii) 800 W for 1.5 min (microwave); iii) three 12-h freeze-thaw cycles at −20 °C; iv) 15,000 rpm for 7 min (high-speed homogenization); and v) 40 kHz for 10 min (sonication).Sonication and freeze-thaw cycles followed by sonication revealed to be the most effective methodologies to ensure a maximum intracellular organic matter release and, consequently, microcystin availability for being extracted. The decrease of cells' viability was however more evident in freeze-thaw cycles, freeze-thaw cycles followed by sonication, and microwave where only 0.3, 0.05 and 0.9% of the initial cells, respectively, maintained their viability after being treated. On the other hand, sonication and bead milling reduced the viability of the original culture to 5 and 15.5%, respectively, while high-speed homogenization did not show any significant differences compared to control.According to the results obtained in this study, the most suitable methodology to maximize the release of microcystin was therefore the use of sonication (40 kHz) during 10 min.