Comparative analyses of H2 photoproduction in magnesium- and sulfur-starved Chlamydomonas reinhardtii cultures.

Magnesium (Mg)-deprived Chlamydomonas reinhardtii cells are capable to sustain hydrogen (H2 ) photoproduction at relatively high photosystem II (PSII) activity levels for an extended time period as compared with sulfur (S)-deprived cells. Herein, we present a comparative study of H2 photoproduction induced by Mg and S shortage to unravel the specific rearrangements of the photosynthetic machinery and cell metabolism occurring under the two deprivation protocols. The exhaustive analysis of photosynthetic activity and regulatory pathways, respiration and starch metabolism revealed the specific rearrangements of the photosynthetic machinery and cellular metabolism, which occur under the two deprivation conditions. The obtained results allowed us to conclude that the expanded time period of H2 production upon Mg-deprivation is due to the less harmful effects that Mg-depletion has on viability and metabolic performance of the cells. Unlike S-deprivation, the photosynthetic light and dark reactions in Mg-deprived cells remained active over the whole H2 production period. However, the elevated PSII activity in Mg-deprived cells was counteracted by the operation of pathways for O2 consumption that maintain anaerobic conditions in the presence of active water splitting.

Controlled influence of quantum dots on purple membranes at interfaces.

The development of bio-sensitized nanofilms engineered from biomembrane components and inorganic nanoparticles is a promising field of colloid and interface science and technologies. Recent nano-bioengineering approaches employing quantum dots (QDs) permit the enhancement of the purple membrane (PM) "light-harvesting capacity" compared to native PMs. The influence of QDs on the PM properties, especially the bacteriorhodopsin (bR) photocycle, has been found that has both fundamental (mechanisms of photoreception) and applied implications (including the fabrication of hybrid bionanomaterials). Samples of PM-QD complexes capable of energy transfer and characterized by increased rates of M-intermediate formation and decay have been obtained. The modified bR photocycle kinetic parameters may be explained by changes in the PM interface upon QD adsorption. The increase and decrease in absorption at 410 nm (or photopotential) for PM-QD complexes are, on average, several times more rapid than for PM suspensions or PM dry films. These results provide a strong impetus for the development of nanomaterials with advanced properties.