Hydrogen peroxide and salinity stress act synergistically to enhance lipids production in microalga by regulating reactive oxygen species and calcium

Abstract

The main purpose of the present study is to evaluate the effects of the combined salt stress and hydrogen peroxide (H2O2) treatment on the accumulation of lipids in Monoraphidium sp. QLY-1. Furthermore, to study the regulatory networks involved in the growth and development of microalgae, the relationships between reactive oxygen species (ROS), Ca2+ and mitogen-activated protein kinase (MAPK) under salinity stress were also analyzed. The results showed that the maximal lipid productivity (107.25 mg L−1 d−1) was achieved under combined 1 mM H2O2 and 171.12 mM (10 g L−1) NaCl treatment, which was 14.28% and 43.31% higher than the 171.12 mM NaCl treatment alone and the control, respectively. The protein content and levels of endogenous ROS, Ca2+ were increased and the expression levels of four lipogenic genes and MAPK were enhanced, while the contents of carbohydrate and chlorophyll were decreased under H2O2 and NaCl treatment. Further research indicated that the increased cytosolic Ca2+ level could alleviate the H2O2-induced oxidative stress under salinity stress by activating glutathione (GSH) activity and modulating calmodulin (CaM) and MAPK expression levels, resulting in biomass modulation and lipid accumulation. The present study provides an effective strategy to improve the lipid production in Monoraphidium sp. QLY-1 using combined H2O2 treatment with salinity stress, and offers evidence of crosstalk between ROS, Ca2+ in the regulation of cell growth and lipid synthesis in microalgae under abiotic stress.