Fixation of high concentration CO2 using Chlorella – Bacteria symbiosis system

The mutualistic interaction between microalgae and bacteria provides a new strategy for improving carbon fixation by microalgae. In this study, Chlorella was co-cultured with natural flora at 15 % (v/v) CO₂ concentration for 120 d. Three Chlorella symbiotic bacteria strains were identified and were co-cultured with Chlorella vulgaris HL02 (C. vulgaris HL02) to fix high concentrations of CO₂. The results showed that the symbiotic bacteria significantly enhanced the fixation of 15 % CO₂ by Chlorella, with C. vulgaris HL02 + Aeromonas GS-HL01 having the highest carbon fixation efficiency, which was 22.31 % higher than that of the sterile control, followed by C. vulgaris HL02 + Bacillus GS-F03, and C. vulgaris HL02 + Microbacterium GS-H02 (which was also 16.36 % higher than the sterile control). The composition of harvested Chlorella was not altered significantly following co-culturing with bacteria. Scanning electron microscopy and Excitation–emission matrix spectra analyses showed that at high concentrations of CO₂, Microalgae and bacteria promote mutual growth and CO₂ fixation mainly through extracellular secretion of organic matter. Our results provided a new strategy to improve the efficiency of microalgae in fixing high concentration of CO₂.