Effects of biological and physical properties of microalgae on disruption induced by a low-frequency ultrasound

Abstract

Ultrasonication has drawn an increasing attention as one of cell disruption methods for extracting cellular compounds or controlling algal blooms. However, the effects of biological and physical properties of microalgae on cell disruption were not well understood. In this work, cell disruption of six microalgae, namely, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Microcystis aeruginosa (three strains: PCC 7806, FACHB 469, and FACHB 1343), and Synechococcus elongatus, was compared mutually based on their characteristics induced by a low-frequency ultrasound (35 kHz, 0.043 W mL−1). Results showed that the most sensitive strain was C. reinhardtii which has a hydroxyproline-rich-glycoproteins cell wall and a larger cell size (normally 10 μm in diameter). More than 80% of the cells of C. reinhardtii were ruptured after sonication for 5 min. In comparison, C. pyrenoidosa, a cellulose-rich-wall algal species with a medium size of 4–6 μm, and M. aeruginosa FACHB 1343, a peptidoglycan-wall species with a smaller average size of 2.3 μm, were highly resistant to ultrasound. Only 7.5 and 7.7% of cell disruption were achieved for C. pyrenoidosa and M. aeruginosa FACHB 1343, respectively, when they were sonicated for 60 min. Declumping effect was dominant in these strains. This suggested that cellulose-rich-wall algal species might be much more resistant than hydroxyproline-rich glycoproteins, and peptidoglycan-wall species to sonication. It also revealed that the larger cell size was more susceptible to sonication the cell would be. This research provides useful insights into choosing the low-cost microalgae for extraction or controlling specific microalgal blooms in water systems using ultrasound.