Hydrophobic Modification of Antenna Chlorophyll in Chlorobium During Growth with Acetylene

Frigaard, Niels-Ulrik; Ormerod, John G.

doi:10.1007/978-94-009-0173-5_36

Cited by 3 publications

(3 citation statements)

References 8 publications

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“…6B). A similar increase in the most highly methylated BChl c homologs was observed when the total BChl c synthesis was inhibited by acetylene treatment (Frigaard and Ormerod 1995).…”

Section: Pigment Analyses Of Mutant Strainssupporting

confidence: 63%

Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum

2009

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The first committed step in the biosynthesis of (bacterio-)chlorophyll is the insertion of Mg2+ into protoporphyrin IX by Mg-chelatase. In all known (B)Chl-synthesizing organisms, Mg-chelatase is encoded by three genes that are homologous to bchH, bchD, and bchI of Rhodobacter spp. The genomes of all sequenced strains of green sulfur bacteria (Chlorobi) encode multiple bchH paralogs, and in the genome of Chlorobaculum tepidum, there are three bchH paralogs, denoted CT1295 (bchT), CT1955 (bchS), and CT1957 (bchH). Cba. tepidum mutants lacking one or two of these paralogs were constructed and characterized. All of the mutants lacking only one of these BchH homologs, as well as bchS bchT and bchH bchT double mutants, which can only produce BchH or BchS, respectively, were viable. However, attempts to construct a bchH bchS double mutant, in which only BchT was functional, were consistently unsuccessful. This result suggested that BchT alone is unable to support the minimal (B)Chl synthesis requirements of cells required for viability. The pigment compositions of the various mutant strains varied significantly. The BChl c content of the bchS mutant was only approximately 10% of that of the wild type, and this mutant excreted large amounts of protoporphyrin IX into the growth medium. The observed differences in BChl c production of the mutant strains were consistent with the hypothesis that the three BchH homologs function in end product regulation and/or substrate channeling of intermediates in the BChl c biosynthetic pathway.

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“…6B). A similar increase in the most highly methylated BChl c homologs was observed when the total BChl c synthesis was inhibited by acetylene treatment (Frigaard and Ormerod 1995).…”

Section: Pigment Analyses Of Mutant Strainssupporting

confidence: 63%

Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum

2009

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“…BChl c biosynthesis is very strongly inhibited by anaesthetic gases, such as ethylene, acetylene, and nitrous oxide (10,26). When Chlorobium sp.…”

Section: Discussionmentioning

confidence: 99%

Chlorobium tepidum Mutant Lacking Bacteriochlorophyll c Made by Inactivation of the bchK Gene, Encoding Bacteriochlorophyll c Synthase

2002

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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 mol 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 lightharvesting antennae.

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“…If removal of the C-13 2 carboxylate moiety occurs after chelation, then Chlide a would seem to be the most logical substrate and would lead to the production of [3-vinyl] Anesthetic gases, such as ethylene, acetylene or N 2 O, have been found to inhibit BChl d synthesis but not BChl a formation in Chl. vibrioforme, and they cause the accumulation of Mg-Proto monomethyl ester (Ormerod et al, 1990;Frigaard and Ormerod, 1995). One interpretation of this observation is that the anesthetic gases inhibit an enzyme that is specifi c for BChl d biosynthesis, most likely the one involved 2 carboxylate or methylcarboxylate group.…”

Section: B Bacteriochlorophyll Biosynthesis Genes In Chloroflexus Aumentioning

confidence: 94%

Bacteriochlorophyll Biosynthesis in Green Bacteria

Frigaard

Chew

Maresca

et al.

Advances in Photosynthesis and Respiration

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Hydrophobic Modification of Antenna Chlorophyll in Chlorobium During Growth with Acetylene

Cited by 3 publications

References 8 publications

Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum

Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum

Chlorobium tepidum Mutant Lacking Bacteriochlorophyll c Made by Inactivation of the bchK Gene, Encoding Bacteriochlorophyll c Synthase

Bacteriochlorophyll Biosynthesis in Green Bacteria

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