Ecology and Physiology of the Competition for Light Between Chlorobium limicola and Chlorobium phaeobacteroides in Natural Habitats

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Abstract
Accurate studies of the pigment composition and isolation in pure cultures of Chlorobiaceae from samples of 8 Spanish lakes show that there are 2 main coexisting groups of green and brown Chlorobium spp., represented, respectively, by C. limicola and C. phaeobacteroides. Laboratory experiments with pure and mixed cultures of the isolated strains show that light quality plays a selective role on the species composition among Chlorobiaceae. This selection depends on the pigment composition which determines the in vivo absorption spectrum of the cells and on their ability to adjust the intracellular concentration of light-harvesting pigments to the spectral distribution and energy of light. Correlation analysis performed with field data resulted in significant, but low, correlation coefficients. Nevertheless, they were consistent with laboratory data showing that brown Chlorobiaceae were dominant in deep layers in meromictic lakes and green Chlorobiaceae dominated in layers nearer the surface or underneath plates of Chromatiaceae. These laboratory and field observations stress the role of biological light filtering in determining the species composition among Chlorobiaceae in lakes.