Pigment variation in the photosynthetic sulfur bacterium Chlorobium phaeobactereoides from Lake Kinneret

Abstract

The photosynthetic sulfur bacterium Chlorobium phaeobactereoides found in Lake Kinneret harbors three homologues of bacteriochlorophyll e (Bchl e). The ratios between the Bchl e homologues found in samples from the metalimnion are approximately constant and perennially stable. The proportion of Bchl e homologues in a laboratory isolate of Ch. phaeobactereoides was different from that found in the lake population, but resistant to changes in light, even if cultures were exposed to light intensity 2-3 orders of magnitude higher than the intensity experienced by the bacterium under natural conditions. Exposure of cultures in the lake did not induce changes in the proportion of pigments, indicating that the isolate maintained in the culture collection is intrinsically different from the genotypes that build up most of Ch.phaeobactereoides in Lake Kinneret. We found a positive relationship between light intensity and carotenoid content in laboratory experiments implying the photoprotective role of those compounds. The laboratory isolate also showed two unknown carotenoids, never found before in lake samples. Those carotenoids are less polar than -carotene, and showed absorption peaks at 427 and 451 nm, and 429 and 451 nm, in methanol.