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B L Marrs

Publications and source records attributed to B L Marrs.

27 records · Page 2Linked to original sources
PubMed1983

Isolation and characterization of enhanced fluorescence mutants of Rhodopseudomonas capsulata.

After enrichment by a tetracycline suicide under conditions nonpermissive for the growth of mutants defective in photosynthesis, colonies were screened for enhanced fluorescence in near-infrared light by using high-speed infrared photography. Twenty mutants were isolated, and the chromatophore membranes were analyzed by a new, rapid microprocedure that revealed many different phenotypes among the mutants. The enhanced fluorescence mutants typically possessed a functional light-harvesting II antenna, but showed reduced or absent light-harvesting I. Twelve isolates were also defective in reaction center polypeptides. An R-prime plasmid that bears 50 kilobases of Rhodopseudomonas capsulata DNA coding for components of the photosynthetic apparatus (B. L. Marrs, J. Bacteriol. 146:1003-1012, 1981), pRPS404, complemented all 20 enhanced fluorescence mutants as demonstrated by the quenching of fluorescence in mutants that had received the R-prime plasmid by conjugation. Fluorescence was regained upon loss of the 50-kilobase insert. Complementation of the fluorescent lesions implies that most or all of the genes necessary for the expression of the reaction center and the light-harvesting antennae are carried by the R-prime plasmid and that these genes are actively transcribed in the homologous organism. All 20 mutants are complemented by one of two pBR322 subclones of the R-prime plasmid, pRPSEB2 or pRPSE2. pRPSEB2 bears a 4.5-kilobase fragment of R. capsulata DNA including the rxcA locus, and pRPSE2 is a pBR322 derivative bearing a 7.5-kilobase R. capsulata DNA fragment bearing the rxcB locus. These fragments therefore carry sequences necessary for the normal synthesis of the light-harvesting and reaction center polypeptide complexes.

Bacterial Proteins↗
PubMed1983

Transcriptional regulation of several genes for bacteriochlorophyll biosynthesis in Rhodopseudomonas capsulata in response to oxygen.

Although it has been shown that bacteriochlorophyll synthesis in Rhodopseudomonas capsulata is repressed by oxygen and high light intensity, few details of regulation by these environmental factors are known, primarily owing to a lack of assays for the biosynthetic enzymes. We have examined regulation at the transcriptional level by isolating and studying fusions between the Mu d1(Apr lac) phage and various bch genes. In these strains, the lacZ gene of the phage is under the control of bch gene promoters. We have found that atmospheric oxygen tension (20% O2) reduces the expression of these fusions at least twofold compared with low oxygen tension (2% O2). Therefore, transcription of the bchA, bchB, bchC, bchG, and bchH genes is regulated in response to oxygen.

Bacteriochlorophylls↗
PubMed1980

Spectral and functional comparisons between the carotenoids of the two antenna complexes of Rhodopseudomonas capsulata.

The spectral and functional properties of carotenoids associated with each of the two light-harvesting complexes of the Rhodopseudomonas capsulata photosynthetic antenna system have been distinguished by studying mutants lacking one or the other complex. In mutants containing only the light-harvesting I complex (LH-I), the absorption spectrum of the carotenoids is blue-shifted compared to wild type. Carotenoid absorption in mutants possessing only the light-harvesting II complex (LH-II) complex is red-shifted. The circular dichroism spectrum of carotenoids in each complex is also distinctive. Although carotenoids in each complex function with approximately the same efficiency in harvesting and transmitting light energy for photosynthesis, only the carotenoids associated with LH-II undergo an electrochromic bandshift upon generation of a transmembrane potential. These observations are interpreted to indicate that both the orientation of carotenoid molecules with respect to the plane of the membrane, and the immediate electrochemical environment of these molecules differ in the two light-harvesting complexes.

Bacterial Chromatophores↗
PubMed1980

Biosynthesis of carotenoids derived from neurosporene in Rhodopseudomonas capsulata.

We have characterized the carotenoids accumulated by a series of mutants of Rhodopseudomonas capsulata as part of a study of the synthesis, structure, and function of the photosynthetic membranes of this bacterium. The carotenoids in this study were identified by visible and mass spectroscopy, chromatography, derivatization, and chemical analyses. We have located a new genetic region, crtF, necessary for the O-methylation of the carotenoids. Mutants with a lesion in crtF accumulate demethylspheroidene as their major carotenoid during anaerobic growth and demethylspheroidenone when grown in the presence of oxygen, a heretofore undescribed phenotype. The genetic region necessary for O-methylation maps adjacent to the known cluster of genes affecting carotenoid biosynthesis. In addition, we have identified methoxyneurosporene as the carotenoid that preferentially binds to the reaction centers of strain Ga, a green mutant of R. sphaeroides which accumulates three neurosporene-like carotenoids. A metabolic grid for carotenoid biosynthesis is proposed, based upon the intermediates accumulated in these mutants.

Alleles↗
PubMed1976

The branched respiratory system of photosynthetically grown Rhodopseudomonas capsulata.

Various respiratory electron transport activities of Rhodopseudomonas capsulata were studied in membrane fragments prepared from photosynthetically grown cells of a parental strain and two terminal oxidase-defective mutant strains. The NADH and succinate oxidase activities of the mutant having a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M6, were consideraly more sensitive to inhibition by either antimycin A or cyanide than the corresponding activities of the mutant lacking a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M7. The parental strain, Z-1, but not the mutants, showed biphasic inhibitory responses of NADH and succinate oxidase activities with either antimycin A or cyanide. In certain reactions no differences in inhibitor susceptibility were found among the strains tested, implying that the pathways involved were unaffected in the mutants. In this category were the actions of rotenone on NADH oxidase, antimycin A on cytochrome c reductase and, in M6 and Z-1, cyanide on N,N,N'N'-tetramethyl-p-phenylenediamine oxidase. These results suggest that the respiratory chain of the parental strain branches at the ubiquinone-cytochrome b region into two pathways, each branch goes to a distinct terminal oxidase, and either may be blocked independently by genetic mutation.

Antimycin A↗
PubMed1976

Isolation and description of a menaquinone mutant from Bacillus licheniformis.

A menaquinone mutant (SG1) of Bacillus licheniformis has been isolated by selecting for colonies that are resistant to low levels of kanamycin (1.5 mug/ml) but sensitive to the same concentration of kanamycin in the presence of shikimate (25 mug/ml). The wild type (IU1) contained 0.38 +/- 0.02 nmol of menaquinone-7 (MK-7) per mg (dry weight) of cells when grown +/- shikimate, whereas SG1 had less than 0.01 nmol of MK-7 per mg (dry weight) of cells when grown in the presence of shikimate. SG1 had a generation time of 85 min, as compared to 24 min for IU1 grown +/- shikimate. SG1 doubled with a generation time of 28 min when grown in the presence of shikimate. IU1 consumed O2 at various rates depending on the stage of growth. A triphasic O2 consumption curve with maxima at mid-exponential phase, the transition from exponential to stationary phase, and early stationary phase was found for IU1 +/- shikimate and SG1 + shikimate. SG1 grown without shikimate consumed O2 at a low level (10 to 20% of IU1). Normal respiration could be restored to SG1 8.5 min after shikimate addition, whereas normal growth was not restored until 40 min after shikimate addition. Electron microscopic studies of SG1 and IU1 have indicated a morphological alteration in the mutant. SG1 is a dwarf cell as compared to IU1, when grown without shikimate. However, SG1 grown with shikimate became morphologically indistinguishable from IU1.

Bacillus↗