Glycerolipid remodeling is crucial for acclimation to naphthenic acid exposure in Chlorella pyrenoidosa and Chlamydomonas reinhardtii

Abstract

Naphthenic acids (NAs) serve as natural components of petroleum, and have turned into essential pollutants in wastewater discharged from various petroleum industries. Some NAs could elicit toxicity towards multiple organisms. Microalgae from culture collections and the indigenous algal strains have been tested for their capacity to tolerate and biodegrade NAs. It is necessary to comprehensively assess the physiological response of microalgae to NA exposure, especially the glycerolipid metabolism. In this study, the representative algal strain for wastewater treatment, Chlorella pyrenoidosa and the model green alga, Chlamydomonas reinhardtii, were used to evaluate their responses to a model NA, cyclohexanecarboxylic acid (CHCA), involving growth, photosynthetic activity, cell morphology and glycerolipid metabolism. The results showed that, C. pyrenoidosa cells were not affected in growth performance and cell structure during 9 days of CHCA exposure. However, the growth of C. reinhardtii was retarded, and the surface of the enlarged cells got damaged within 3 days of CHCA treatment. Their photosynthetic activity both remained stable when subjected to CHCA stress. More importantly, the fatty acyl profiles of total lipids, membrane lipids and neutral lipids were all remodeled and C18:3n3 in the two algae serves as the potential biomarker in response to CHCA treatment. Thus, C. pyrenoidosa presented more superior tolerance to CHCA exposure relative to C. reinhardtii, and they both reconstructed the glycerolipid components for acclimation to CHCA stress. Overall, glycerolipid remodeling is crucial for green microalgae to accommodate the NAs-contaminated environment. This study offers valuable insights into the potential tolerance and physiological response of green algae to NA stress, especially in glycerolipid remodeling, which will benefit improved monitoring of NAs pollution in aquatic ecosystems and effective treatment of NA-contaminated wastewater.