Carbon distribution and metabolism mechanism of a novel mixotrophic Chlorella in municipal wastewater

Conventional wastewater treatment technologies primarily convert complex organic matter into dissolved inorganic carbon (DIC) and a more difficult gaseous state CO2. Most microalgae species can photosynthetically assimilate above inorganic carbon, but their heterotrophic metabolic processes often dominate in glucose-mediated mixotrophy. Herein, we investigated the carbon-fixing metabolic pathways of Chlorella sp. MIHQ61 in municipal wastewater containing complex carbon sources. The total carbon removal (73.0 %) peaked on the 6th day, and DIC removal exceeded 50.0 % as the carbon migrating amount from municipal wastewater into the microalgal cells peaked. The glucose and NaHCO3 combination promoted both autotrophic and heterotrophic metabolism. Headspace CO2 emission, enzyme activity and central carbon metabolism results implied heterotrophic metabolism occurred more actively in the early stage and autotrophic metabolism dominated late stage. Redefined mixotrophic carbon allocation by revealing time-dependent autotrophic/heterotrophic interplay. Carbon distribution and mixotrophic mechanism provided new thinking on how to utilize microalgae and wastewater resource.