scholarly journals The Bound Electron Acceptors in Green Sulfur Bacteria: Resolution of the g-Tensor for the FX Iron-Sulfur Cluster in Chlorobium tepidum

2000 ◽  
Vol 78 (6) ◽  
pp. 3160-3169 ◽  
Author(s):  
Ilya R. Vassiliev ◽  
Michael T. Ronan ◽  
Günter Hauska ◽  
John H. Golbeck
Keyword(s):  
Green Sulfur Bacteria ◽  
Electron Acceptors ◽  
Chlorobium Tepidum ◽  
Iron Sulfur Cluster ◽  
Sulfur Cluster ◽  
Sulfur Bacteria ◽  
Iron Sulfur ◽  
Green Sulfur ◽  
Bound Electron

scholarly journals Genetic Manipulation of Carotenoid Biosynthesis in the Green Sulfur Bacterium Chlorobium tepidum

2004 ◽  
Vol 186 (16) ◽  
pp. 5210-5220 ◽  
Author(s):  
Niels-Ulrik Frigaard ◽  
Julia A. Maresca ◽  
Colleen E. Yunker ◽  
A. Daniel Jones ◽  
Donald A. Bryant
Keyword(s):  
Genetic Manipulation ◽  
Sequence Similarity ◽  
Carotenoid Biosynthesis ◽  
Green Sulfur Bacteria ◽  
Chlorobium Tepidum ◽  
Sequence Motifs ◽  
Green Sulfur Bacterium ◽  
Sulfur Bacteria ◽  
Carotenoid Composition ◽  
Green Sulfur

ABSTRACT The green sulfur bacterium Chlorobium tepidum is a strict anaerobe and an obligate photoautotroph. On the basis of sequence similarity with known enzymes or sequence motifs, nine open reading frames encoding putative enzymes of carotenoid biosynthesis were identified in the genome sequence of C. tepidum, and all nine genes were inactivated. Analysis of the carotenoid composition in the resulting mutants allowed the genes encoding the following six enzymes to be identified: phytoene synthase (crtB/CT1386), phytoene desaturase (crtP/CT0807), ζ-carotene desaturase (crtQ/CT1414), γ-carotene desaturase (crtU/CT0323), carotenoid 1′,2′-hydratase (crtC/CT0301), and carotenoid cis-trans isomerase (crtH/CT0649). Three mutants (CT0180, CT1357, and CT1416 mutants) did not exhibit a discernible phenotype. The carotenoid biosynthetic pathway in C. tepidum is similar to that in cyanobacteria and plants by converting phytoene into lycopene using two plant-like desaturases (CrtP and CrtQ) and a plant-like cis-trans isomerase (CrtH) and thus differs from the pathway known in all other bacteria. In contrast to the situation in cyanobacteria and plants, the construction of a crtB mutant completely lacking carotenoids demonstrates that carotenoids are not essential for photosynthetic growth of green sulfur bacteria. However, the bacteriochlorophyll a contents of mutants lacking colored carotenoids (crtB, crtP, and crtQ mutants) were decreased from that of the wild type, and these mutants exhibited a significant growth rate defect under all light intensities tested. Therefore, colored carotenoids may have both structural and photoprotection roles in green sulfur bacteria. The ability to manipulate the carotenoid composition so dramatically in C. tepidum offers excellent possibilities for studying the roles of carotenoids in the light-harvesting chlorosome antenna and iron-sulfur-type (photosystem I-like) reaction center. The phylogeny of carotenogenic enzymes in green sulfur bacteria and green filamentous bacteria is also discussed.

scholarly journals Two Genes Encoding New Carotenoid-Modifying Enzymes in the Green Sulfur Bacterium Chlorobium tepidum

2006 ◽  
Vol 188 (17) ◽  
pp. 6217-6223 ◽  
Author(s):  
Julia A. Maresca ◽  
Donald A. Bryant
Keyword(s):  
Green Sulfur Bacteria ◽  
The Other ◽  
Chlorobium Tepidum ◽  
Green Sulfur Bacterium ◽  
Gene Encoding ◽  
Anoxygenic Phototrophs ◽  
Sulfur Bacteria ◽  
Genes Encoding ◽  
Green Sulfur ◽  
Predicted Function

ABSTRACT The green sulfur bacterium Chlorobium tepidum produces chlorobactene as its primary carotenoid. Small amounts of chlorobactene are hydroxylated by the enzyme CrtC and then glucosylated and acylated to produce chlorobactene glucoside laurate. The genes encoding the enzymes responsible for these modifications of chlorobactene, CT1987, and CT0967, have been identified by comparative genomics, and these genes were insertionally inactivated in C. tepidum to verify their predicted function. The gene encoding chlorobactene glucosyltransferase (CT1987) has been named cruC, and the gene encoding chlorobactene lauroyltransferase (CT0967) has been named cruD. Homologs of these genes are found in the genomes of all sequenced green sulfur bacteria and filamentous anoxygenic phototrophs as well as in the genomes of several nonphotosynthetic bacteria that produce similarly modified carotenoids. The other bacteria in which these genes are found are not closely related to green sulfur bacteria or to one another. This suggests that the ability to synthesize modified carotenoids has been a frequently transferred trait.

scholarly journals The bchU Gene of Chlorobium tepidum Encodes the C-20 Methyltransferase in Bacteriochlorophyll c Biosynthesis

2004 ◽  
Vol 186 (9) ◽  
pp. 2558-2566 ◽  
Author(s):  
Julia A. Maresca ◽  
Aline Gomez Maqueo Chew ◽  
Marta Ros Ponsatí ◽  
Niels-Ulrik Frigaard ◽  
John G. Ormerod ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stop Codon ◽  
Green Sulfur Bacteria ◽  
Infrared Light ◽  
Chlorobium Tepidum ◽  
Spontaneous Mutant ◽  
Reading Frame ◽  
Sulfur Bacteria ◽  
Light Intensities ◽  
Green Sulfur

ABSTRACT Bacteriochlorophylls (BChls) c and d, two of the major light-harvesting pigments in photosynthetic green sulfur bacteria, differ only by the presence of a methyl group at the C-20 methine bridge position in BChl c. A gene potentially encoding the C-20 methyltransferase, bchU, was identified by comparative analysis of the Chlorobium tepidum and Chloroflexus aurantiacus genome sequences. Homologs of this gene were amplified and sequenced from Chlorobium phaeobacteroides strain 1549, Chlorobium vibrioforme strain 8327d, and C. vibrioforme strain 8327c, which produce BChls e, d, and c, respectively. A single nucleotide insertion in the bchU gene of C. vibrioforme strain 8327d was found to cause a premature, in-frame stop codon and thus the formation of a truncated, nonfunctional gene product. The spontaneous mutant of this strain that produces BChl c (strain 8327c) has a second frameshift mutation that restores the correct reading frame in bchU. The bchU gene was inactivated in C. tepidum, a BChl c-producing species, and the resulting mutant produced only BChl d. Growth rate measurements showed that BChl c- and d-producing strains of the same organism (C. tepidum or C. vibrioforme) have similar growth rates at high and intermediate light intensities but that strains producing BChl c grow faster than those with BChl d at low light intensities. Thus, the bchU gene encodes the C-20 methyltransferase for BChl c biosynthesis in Chlorobium species, and methylation at the C-20 position to produce BChl c rather than BChl d confers a significant competitive advantage to green sulfur bacteria living at limiting red and near-infrared light intensities.

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