Evolution of Chlorella sp. RCC288 proteome and transcriptome during its adaptation to oil mill wastewater

Some species of microalgae, including Chlorella, can utilize a variety of dissolved organic carbon sources, such as sugars and organic acids, for growth. In the presence of both light and these organic substrates, they exhibit mixotrophic metabolism, combining heterotrophic assimilation of organic carbon with photosynthetic carbon fixation. In this study, we analyzed using proteomic and transcriptomic approaches the ability of Chlorella sp. to shift its metabolism when it was grown in photoautotrophy in BG-11 medium and mixotrophy in 30 % diluted olive mill wastewaters (OMWWs) pretreated with laccases. Using UniProt, InterPro, KEGG Pathway, and Gene Ontology databasesproteomic and transcriptomic data have been analyzed. In mixotrophy, over-expression of cell cycle, signaling, and transport proteins, as well as chaperone proteins, were identified and associated with an overall decrease in photosynthesis and carbohydrate/lipid metabolic pathways. In addition, the expression of light-independent protochlorophyllide reductase, malate synthase, acetyl-CoA carboxylase and pyruvate kinase were modulated. Surprisingly an upregulation of the ammonium transporter protein, which could play a role in OMWWs detoxification was detected. Homology modeling investigation of the three-dimensional structure of ammonium transporter protein revealed that it holds a functional trimeric structure with a lengthy C-terminal region that may be involved in the regulation and activation of ammonium transport.