Biohydrogen production by purple non-sulfur bacteria Rhodobacter sphaeroides: Effect of low-intensity electromagnetic irradiation

The present work was focused on the effects of low-intensity (the flux capacity was of 0.06 mW cm− 2) electromagnetic irradiation (EMI) of extremely high frequencies or millimeter waves on the growth and hydrogen (H2) photoproduction by purple non-sulfur bacteria Rhodobacter sphaeroides MDC6521 (from Armenian mineral springs). After exposure of R. sphaeroides, grown under anaerobic conditions upon illumination, to EMI (51.8 GHz and 53.0 GHz) for 15 min an increase of specific growth rate by ~ 1.2-fold, in comparison with control (non-irradiated cells), was obtained. However, the effect of EMI depends on the duration of irradiation: the exposure elongation up to 60 min caused the delay of the growth lag phase and the decrease specific growth rate by ~ 1.3-fold, indicating the bactericidal effect of EMI. H2 yield of the culture, irradiated by EMI for 15 min, determined during 72 h growth, was ~ 1.2-fold higher than H2 yield of control cells, whereas H2 production by cultures, irradiated by EMI for 60 min was not observed during 72 h growth. This difference in the effects of extremely high frequency EMI indicates a direct effect of radiation on the membrane transfer and the enzymes of these bacteria. Moreover, EMI increased DCCD-inhibited H+ fluxes across the bacterial membrane and DCCD-sensitive ATPase activity of membrane vesicles, indicating that the proton FoF1-ATPase is presumably a basic target for extremely high frequency EMI related to H2 production by cultures.