Abstract
We determined the wavelength dependence of the specific growth rate of Rhodopseudomonas sphaeroides (the action spectrum of growth). A half-maximal (light-limited) growth rate was obtained when the culture vessel was illuminated with photon intensities between 0.8 x 10(14) and 3.5 x 10(14) photons cm-2 s-1 in the wavelength region between 400 and 950 nm. In the action spectrum, measured at 1.25 x 10(14) photons cm-2 s-1, distinct peaks could be observed at 480, 580, 800, and 870 nm, and minima could be found at 420, 540, 640 to 730, 830, and 940 nm. Both the pigment content and pigment composition of R. sphaeroides varied, depending on the wavelengths of the actinic light used for growth. This demonstrates that chromatic adaptation occurs in this bacterium.