Photobiotechnology: Algal Hydrogen Production and Photoconductivity of Metalized Chloroplasts

Sustained hydrogen photoevolution from Chlamydomonas reinhardtii and C. moewusii was measured under an anoxic, CO₂-containing atmosphere. It has been discovered that light intensity and temperature influence the partitioning of reductant between the hydrogen photoevolution pathway and the Calvin cycle. Under low incident light intensity (1-3 W m^-2) or low temperature (approx. 0°C), the flow of photosynthetic reductant to the Calvin cycle was reduced, and reductant was partitioned to the hydrogen pathway as evidenced by sustained H₂ photoevolution. Under saturating light (25 W m^-2) and moderate temperature 20 ± 5°C, the Calvin cycle became the absolute sink for reductant with the exception of a burst of H₂ occurring at light on. A novel photobiophysical phenomenon was observed in isolated spinach chloroplasts that were metalized by precipitating colloidal platinum onto the surface of the thylakoid membranes. A two-point irradiation and detection system was constructed in which a continuous beam helium-neon laser (λ = 632.8 nm) was used to irradiate the platinized chloroplasts at varying perpendicular distances from a single linear platinum electrode in pressure contact with the platinized chloroplasts. No external voltage bias was applied to the system. The key objective of the experiments reported in this report was to measure the relative photoconductivity of the chloroplast-metal composite matrix.