Role of ground and excited singlet state oxygen in the red light-induced stimulation of Escherichia coli cell growth

Irradiation of selected Escherichia coli defective strains with red-light i nduces a stimulation of the cell growth rate. Such effect is wavelength-dep endent and is accompanied by a transient increase of the cell volume and so me enzymic activities. The presence of oxygen appears to be essential for t he occurrence of a significant photostimulatory effect. The results obtaine d upon irradiation in the presence of quenchers (tryptophan, histidine, azi de) or enhancers (deuterium oxide) of singlet oxygen (O-1(2)) strongly sugg est that this activated oxygen derivative is generated by excitation of end ocellular chromophores (possibly cytochromes), The reaction of O-1(2) with nearby cellular targets could induce a sublethal cell damage which in turn promotes an accelerated cell metabolism. (C) 1999 Academic Press.