Scaling-up and proteomic analysis reveals photosynthetic and metabolic insights toward prolonged H2 photoproduction in Chlamydomonas hpm91 mutant lacking proton gradient regulation 5 (PGR5).

Clean and sustainable H2 production is crucial to a carbon-neutral world. H2 generation by Chlamydomonas reinhardtii is an attractive approach for solar-H2 from H2O. However, it is currently not large-scalable because of lacking desirable strains with both optimal H2 productivity and sufficient knowledge of underlying molecular mechanism. We hereby carried out extensive and in-depth investigations of H2 photoproduction of hpm91 mutant lacking PGR5 (Proton Gradient Regulation 5) toward its up-scaling and fundamental mechanism issues. We show that hpm91 is at least 100-fold scalable (up to 10 L) with continuous H2 collection of 7287 ml H2/10L-HPBR in averagely 26 days under sulfur deprivation. Also, we show that hpm91 is robust and active during sustained H2 photoproduction, most likely due to decreased intracellular ROS relative to wild type. Moreover, we obtained quantitative proteomic profiles of wild type and hpm91 at four representing time points of H2 evolution, leading to 2229 and 1350 differentially expressed proteins, respectively. Compared to wild type, major proteome alterations of hpm91 include not only core subunits of photosystems and those related to anti-oxidative responses but also essential proteins in photosynthetic antenna, C/N metabolic balance, and sulfur assimilation toward both cysteine biosynthesis and sulfation of metabolites during sulfur-deprived H2 production. These results reveal not only new insights of cellular and molecular basis of enhanced H2 production in hpm91 but also provide additional candidate gene targets and modules for further genetic modifications and/or in artificial photosynthesis mimics toward basic and applied research aiming at advancing solar-H2 technology.

[Influence of glucose concentration on the inhibition of Streptococcus oligofermentans on Streptococcus mutans].

OBJECTIVE: To investigate the inhibition of Streptococcus oligofermentans (So) on Streptococcus mutans (Sm) and the producibility of hydrogen peroxide by So under the influence of glucose concentration environment. METHODS: The inhibition between So and Sm was observed by plating method under the different glucose concentration environment. The initial synthesis rates and production of hydrogen peroxide by So were determined under the different glucose concentration environment by 4-aminoantipyine-horseradish peroxidase method at A(510). RESULTS: Under 0, 10 and 50 mmol/L glucose environment, the inhibition of So on Sm was evident. When both Sm and So were inoculated at the same time, the ratio of inhibition area by bacterial membrane area was 0.202 ± 0.005, 0.467 ± 0.025, 0.468 ± 0.028 under 0, 10, 50 mmol/L glucose environment. When So was cultivated first and then Sm applied, the ratio was 0.394 ± 0.004, 0.811 ± 0.075 and 0.816 ± 0.007 under 0, 10 and 50 mmol/L glucose environment respectively. The inhibition under 10 and 50 mmol/L glucose environment were more significant than that under non-glucose environment. There was no significant difference between these two glucose concentrations (P > 0.05). The initial synthesis rates of H2O2 by So under the 10 mmol/L [(23.573 ± 0.263) µmo×L(-1)×min(-1)] and 50 mmol/L [(23.337 ± 0.473) µmol×L(-1)×min(-1)] glucose were higher than without glucose[(10.513 ± 0.516) µmol×L(-1)×min(-1)], P < 0.05. H2O2 was not detected in 1000 mmol/L glucose. However, the production of H2O2 by So under 0 mmol/L glucose was higher than other glucose concentrations (P < 0.05). CONCLUSIONS: The capability of the inhibition of So on Sm was affected by glucose environment and was much stronger under certain glucose concentrations (10, 50 mmol/L).

[The influence of oxygen on the inhibition between Streptococcus oligofermentans and Streptococcus mutans].

OBJECTIVE: To investigate the effect of environmental oxygen on the inhibition between Streptococcus oligofermentans (So) and Streptococcus mutans (Sm) and the producibilities of hydrogen peroxide by So. METHODS: The aerobic and anaerobic environment was established by the carbon dioxide cultivation. The inhibition between So and Sm was observed by plating method. The production and synthesis rates of hydrogen peroxide by So were determined in both aerobic and anaerobic environment by 4-ATTP-horseradish peroxidase method at A(510). RESULTS: When both Sm and So were inoculated at the same time, Sm was not inhibited under the anaerobic environment, vice versa. Sm was slightly inhibited by So under the aerobic environment, the inhibition area was 1/5 of all bacterial membrane. When So was cultivated first and then Sm applied, So could inhibite Sm growth under both anaerobic and aerobic conditions. The inhibition area was 1/5 of bacterial membrane under the anaerobic environment, and 4/5 under the aerobic environment. When Sm was cultivated first and then So applied, So was unable to proliferate under both conditions. During the logarithmic phase, the production of H2O2 by So under the aerobic environment was higher than under the anaerobic environment (P < 0.05). The initial synthesis rate of H2O2 by So during growth cycle under the anaerobic condition was (11.84 ± 3.97) µmol/L per minute, which was only 49% of that under the aerobic environment [(24.13 ± 4.46) µmol/L per minute]. CONCLUSIONS: The oxygen has the effect on the inhibition between So and Sm, and the inhibition in the aerobic environment is much stronger than in the anaerobic environment. The synthesis ability of hydrogen peroxide by So under the aerobic environment is higher than under the anaerobic environment.