LIGHT ENVIRONMENT AND SYNTHESIS OF BACTERIOCHLOROPHYLL BY POPULATIONSOF CHROMATIUM-OKENII UNDER NATURAL ENVIRONMENTAL-CONDITIONS

In the meromictic alpine Lake Cadagno a dense layer of phototrophic ba cteria, mainly Chromatium okenii and Amoebobacter purpureus, develop a nnually at the chemocline at about 10 to 11 m depth. Radiometric spect ral profiles of the incident sunlight demonstrate different attenuatio n coefficients in the mixolimnion and in the chemocline not only for t he visible light effective at each depth (photosynthetically available radiation), but also for selected photosynthetically active wavelengt hs used by oxygenic and anoxygenic phototrophs. Phototrophic bacteria sampled from the upper part of the layer at the maximum of cell concen tration were incubated in transparent bottles at the sampling depth an d at a lower depth where the light intensity is only a few percent of the one at the sampling depth. Within 4 h the specific bacteriochlorop hyll concentration (Bchl protein(-1)) increased up to 50% depending on the difference in Light intensity between the sampling and the incuba tion depth. The specific bacteriochlorophyll concentration in the uppe r part of the layer remained constant (53.0 mg Bchl g(-1) protein, S.D . = 4.8) in spite of large changes in cell concentrations in the lake water over the season. These observations illustrate the phenomenon of light-regulated pigment synthesis under natural conditions.