RESUMEN
The pigment composition of "Candidatus Chlorothrix halophila," a filamentous anoxygenic phototrophic bacterium found in Baja California Sur, Mexico, was determined. Previous work showed that bacteriochlorophyll c (BChl c) was the major pigment in "Ca. Chlorothrix halophila," but it was not clear if this bacterium also contains BChl a (J. A. Klappenbach and B. K. Pierson, Arch. Microbiol. 181:17-25, 2004). Here we show that in addition to BChl c, a small amount of a pigment that is spectrally indistinguishable from BChl a is present in cell extracts of "Ca. Chlorothrix halophila." Nevertheless, the BChl a-like pigment from "Ca. Chlorothrix halophila" has a different molecular weight and a different high-performance liquid chromatography elution time than BChl a from other photosynthetic bacteria. Based on mass spectrometry and other spectroscopic analysis, we determined that the BChl a-like pigment in "Ca. Chlorothrix halophila" contains a tetrahydrogeranylgeraniol tail rather than the phytol tail that is present in BChl a. The carotenoids and major BChl c homologs in "Ca. Chlorothrix halophila" were also identified. BChls c were found to be farnesol esterified and geranylgeraniol esterified.
Asunto(s)
Chloroflexi/metabolismo , Pigmentos Biológicos/análisis , Proteínas Bacterianas/análisis , Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Bacterioclorofila A/análisis , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Bacterioclorofilas/análisis , Bacterioclorofilas/química , Bacterioclorofilas/metabolismo , Carotenoides/análisis , Carotenoides/química , Carotenoides/metabolismo , Chloroflexi/ultraestructura , Cromatografía Líquida de Alta Presión , Microscopía Electrónica de Transmisión , Estructura Molecular , Pigmentos Biológicos/química , Pigmentos Biológicos/metabolismo , Espectrometría de Masa por Láser de Matriz Asistida de Ionización DesorciónRESUMEN
Chlorophyll d-producing cyanobacteria are a recently described group of phototrophic bacteria that is a major focus of photosynthesis research, previously known only from marine environments in symbiosis with eukaryotes. We have discovered a free-living member of this group from a eutrophic hypersaline lake. Phylogenetic analyses indicated these strains are closely related to each other but not to prochlorophyte cyanobacteria that also use an alternative form of chlorophyll as the major light-harvesting pigment. We have also demonstrated that these bacteria acquired a fragment of the small-subunit rRNA gene encoding a conserved hairpin in the bacterial ribosome from a proteobacterial donor at least 10 million years before the present. Thus, our most widely used phylogenetic marker can be a mosaic of sequence fragments with widely divergent evolutionary histories.