High light and temperature enhancing astaxanthin production in Microcystis aeruginosa—Providing a potential thought for controlling cyanobacterial blooms through resource utilization

Abstract

Artificial salvage is the common method to control cyanobacterial blooms that easily outbreak in summer, but the salvaged cyanobacteria are not effectively utilized. Microcystis aeruginosa is a typical species in cyanobacterial blooms and can accumulate astaxanthin. To promote cyanobacterial blooms control through producing astaxanthin as resource utilization manner, the algal cell growth, photosynthetic abilities, astaxanthin and its precursor levels as well as related gene expression in M. aeruginosa was investigated under high light (HL) and high temperature (HT), the typical conditions in summer. Under HL and HT conditions, M. aeruginosa cell growth and photosynthetic abilities were reduced, due to the declined chlorophyll content and down-regulated photosynthesis-related gene expression. During the 5 days, the astaxanthin content was gradually increased with elevating the light intensity and temperature, reaching the maximum level under HL at 1000 μmol·m−2·s−1 and HT at 35 °C. However, the precursor (β-carotene and zeaxanthin) levels were gradually decreased. This indicated that HL and HT can promote astaxanthin generation and the precursor transformation, as the expression of the genes related with methylerythritol-4-phosphate pathway and astaxanthin formation was up-regulated. Therefore, summer weather can promote astaxanthin accumulation in cyanobacteria by raising related gene expression. During cyanobacterial blooms in summer, their enormous biomass and high astaxanthin level provide a potential for astaxanthin production, while the cyanobacteria salvaged in other seasons can be cultured under HL (1000 μmol·m−2·s−1) and HT (35 °C) conditions to improve astaxanthin content for extracting the high-value compound, which are beneficial to promoting cyanobacterial blooms control through salvage and resource utilization.