Chlorobium tepidum mutant lacking bacteriochlorophyll c made by inactivation of the bchK gene, encoding bacteriochlorophyll c synthase
Research output: Contribution to journal › Journal article › Research › peer-review
The gene encoding bacteriochlorophyll (BChl) c synthase was identified by insertional inactivation in the photosynthetic green sulfur bacterium Chlorobium tepidum and was named bchK. The bchK mutant of C. tepidum was rusty-orange in color and completely lacked BChl c. Because of the absence of the BChl c antenna, the mutant grew about seven times slower than the wild type at light intensities that were limiting to the wild type (< 90 micromol m(-2) s(-1)). Various pheophorbides, which probably represent precursors of BChl c which had lost magnesium, accumulated in the mutant cells. A small fraction of these pheophorbides were apparently esterified by the remaining chlorophyll (Chl) a and BChl a synthases in cells. The amounts of BChl a, Chl a, isoprenoid quinones, carotenoids, Fenna-Matthews-Olson protein, and chlorosome envelope protein CsmA were not significantly altered on a cellular basis in the mutant compared to in the wild type. This suggests that the BChl a antennae, photosynthetic reaction centers, and remaining chlorosome components were essentially unaffected in the mutant. Electron microscopy of thin sections revealed that the mutant lacked normal chlorosomes. However, a fraction containing vestigial chlorosomes, denoted "carotenosomes," was partly purified by density centrifugation; these structures contained carotenoids, isoprenoid quinones, and a 798-nm-absorbing BChl a species that is probably protein associated. Because of the absence of the strong BChl c absorption found in the wild type, the bchK mutant should prove valuable for future analyses of the photosynthetic reaction center and of the roles of BChl a in photosynthesis in green bacteria. An evolutionary implication of our findings is that the photosynthetic ancestor of green sulfur bacteria could have evolved without chlorosomes and BChl c and instead used only BChl a-containing proteins as the major light-harvesting antennae.
Original language | English |
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Journal | Journal of Bacteriology |
Volume | 184 |
Issue number | 12 |
Pages (from-to) | 3368-3376 |
Number of pages | 8 |
ISSN | 0021-9193 |
DOIs | |
Publication status | Published - 2002 |
Bibliographical note
Keywords: Bacterial Proteins; Bacteriochlorophylls; Carbon-Oxygen Ligases; Chlorobi; Light-Harvesting Protein Complexes; Microscopy, Electron; Mutation; Organelles; Photosynthetic Reaction Center Complex Proteins; Pigments, Biological
ID: 14095611