Simazine Enhances Dark Fermentative H(2) Production by Unicellular Halotolerant Cyanobacterium Aphanothece halophytica

The halotolerant cyanobacterium Aphanothece halophytica is a potential H(2) producer that induces H(2) evolution under nitrogen deprivation. H(2) is mainly produced via the catabolism of stored glycogen under dark anaerobic condition. H(2) evolution is catalyzed by O(2)-sensitive bidirectional hydrogenase. The aim of this study was to improve H(2) production by A. halophytica using various kinds of inhibitors. Among all types of inhibitors, simazine efficiently promoted the highest H(2) production under dark conditions. High simazine concentration and long-term incubation resulted in a decrease in cell and chlorophyll concentrations. The optimal simazine concentration for H(2) production by A. halophytica was 25 µM. Simazine inhibited photosynthetic O(2) evolution but promoted dark respiration, resulting in a decrease in O(2) level. Hence, the bidirectional hydrogenase activity and H(2) production was increased. A. halophytica showed the highest H(2) production rate at 58.88 ± 0.22 µmol H(2) g(−1) dry weight h(−1) and H(2) accumulation at 356.21 ± 6.04 μmol H(2) g(−1) dry weight after treatment with 25 µM simazine under dark anaerobic condition for 2 and 24 h, respectively. This study demonstrates the potential of simazine for the enhancement of dark fermentative H(2) production by A. halophytica.