Hydrogen Sulfide Promotes Cell Division and Photosynthesisof Nannochloropsis oceanica with 15% Carbon Dioxide

To improve microalgal growth and CO2 fixation in syngas from coal gasification in the coal chemical industry, the influence of H2S impurities in syngas from coal gasification on the cell division and photosynthesis of Nannochloropsis oceanica was investigated. After N. oceanica cells started an unfolded protein response to overcome the 10 h suppression period for H2S toxicity adaption, the effective photosynthetic electron transport rate and biomass yield increased by 59.6% and 28.2% (in response to 0.5 mM NaHS as the H2S donor). Such a low H2S concentration effectively promoted synthetic reactions of DNA and RNA, translation initiated by eIF-2 with ribosomal proteins, and cytoplasmic division guided by FtsZ, thus accelerating cell division and decreasing cell size. H2S also enhanced the cellular light absorption capacity by up-regulating the contents of both photosynthetic pigments and light-harvesting proteins. Both maximum quantum yield of PSII photochemistry (F-v/F-m) and nonphotochemical quenching (NPQ) increased by 65.5% and 8.8-fold with H2S. H2S alleviated D1 protein degradation by enhancing the electron transfer between the donor side and the recipient side. H2S up-regulated ferredoxin, ferredoxin-NADP(+) reductase, and thioredoxin contents for providing more NADPH and strengthening the Rubisco activity regulation process with the ferredoxinthioredoxin system, which promoted growth under CO2 fixation.