Characterization of two cell-envelope fractions from chemotrophically grown Rhodospirillum rubrum

A rapid method for the extraction and analysis of carotenoids and other hydrophobic substances suitable for systems biology studies with photosynthetic bacteria

A simple, rapid, and inexpensive extraction method for carotenoids and other non-polar compounds present in phototrophic bacteria has been developed. The method, which has been extensively tested on the phototrophic purple non-sulphur bacterium Rhodospirillum rubrum, is suitable for extracting large numbers of samples, which is common in systems biology studies, and yields material suitable for subsequent analysis using HPLC and mass spectroscopy. The procedure is particularly suitable for carotenoids and other terpenoids, including quinones, bacteriochlorophyll a and bacteriopheophytin a, and is also useful for the analysis of polar phospholipids. The extraction procedure requires only a single step extraction with a hexane/methanol/water mixture, followed by HPLC using a Spherisorb C18 column, with a mobile phase consisting of acetone-water and a non-linear gradient of 50%-100% acetone. The method was employed for examining the carotenoid composition observed during microaerophilic growth of R. rubrum strains, and was able to determine 18 carotenoids, 4 isoprenoid-quinones, bacteriochlorophyll a and bacteriopheophytin a as well as four different phosphatidylglycerol species of different acyl chain compositions. The analytical procedure was used to examine the dynamics of carotenoid biosynthesis in the major and minor pathways operating simultaneously in a carotenoid biosynthesis mutant of R. rubrum.

Localization of cytochromes to the outer membrane of anaerobically grown Shewanella putrefaciens MR-1

In gram-negative bacteria, numerous cell functions, including respiration-linked electron transport, have been ascribed to the cytoplasmic membrane. Gram-negative bacteria which use solid substrates (e.g., oxidized manganese or iron) as terminal electron acceptors for anaerobic respiration are presented with a unique problem: they must somehow establish an electron transport link across the outer membrane between large particulate metal oxides and the electron transport chain in the cytoplasmic membrane. When the metal-reducing bacterium Shewanella putrefaciens MR-1 is grown under anaerobic conditions and membrane fractions are purified from cells lysed by an EDTA-lysozyme-polyoxyethylene cetyl ether (Brij 58) protocol, approximately 80% of its membrane-bound cytochromes are localized in its outer membrane. These outer membrane cytochromes could not be dislodged by treatment with chaotropic agents or by increased concentrations of the nonionic detergent Brij 58, suggesting that they are integral membrane proteins. Cytochrome distribution in cells lysed by a French press protocol confirm the localization of cytochromes to the outer membrane of anaerobically grown cells. This novel cytochrome distribution could play a key role in the anaerobic respiratory capabilities of this bacterium, especially in its ability to mediate manganese and iron reduction.

Porin isolated from the cell envelope of Rhodopseudomonas capsulata

The isolate major outer membrane protein from Rhodopseudomonas capsulata St. Louis (ATCC 23782) has a high porin activity in reconstituted phospholipid liposomes. The pore size of the homooligomeric porin with subunits of Mr 33,000 was determined to be about 0.8 nm in radius. Circular dichroism data revealed major portions of the beta structure. Heating of the oligomer resulted in monomer formation, loss of porin activity (60 to 70 degrees C), and change to alpha structure (100 degrees C).

Differences in the architecture of cytoplasmic and intracytoplasmic membranes of three chemotrophically and phototrophically grown species of the Rhodospirillaceae

Freeze-fracture faces of membranes of either chemotrophically or phototrophically grown Rhodospirillum rubrum, Rhodopseudomonas sphaeroides, and Rhodospirillum tenue were analyzed. All three species differed from each other with respect to size as well as numerical density (number per square micrometer) of intramembrane particles. In R. rubrum the number of particles on exoplasmic fracture faces of the cytoplasmic membrane stayed nearly constant (about 900 particles per microns2), but on the plasmic fracture face there were 4,700 and 6,264 particles per microns2, respectively, under chemotrophic and phototrophic conditions. The increase in number was largely a result of an enhanced occurrence of particles 10 nm in diameter. This diameter corresponds to the mean diameter of the predominant class of particles visible on the plasmic fracture faces of intracytoplasmic membrane formed under phototrophic conditions. In R. sphaeroides the number of particles on both of the fracture faces of cytoplasmic membranes stayed nearly constant. The mean diameter of articles appeared to be slightly increased under phototrophic conditions. Particles of cytoplasmic and intracytoplasmic membranes of phototrophically grown cells were of similar diameter. The number of particles, however, on plasmic fracture faces of intracytoplasmic membranes (6,674/microns2) was significantly higher than that on cytoplasmic membranes (5,708/microns2). R. tenue, on the other hand, which does not produce intracytoplasmic membranes, showed on exoplasmic fracture faces 543 and 3,765 particles per micron2 under chemotrophic and phototrophic conditions, respectively, whereas the corresponding numerical densities of plasmic fracture faces were 4,043 and 3,711 particles per microns2. The increased number of articles on exoplasmic fracture faces was mainly the result of an increased occurrence of particles with diameters greater than or equal to 10 nm. The results are interpreted to allow for the different modes of intractyoplasmic membrane development in Rhodospirillum rubrum and Rhodopseudomonas sphaeroides, respectively.

Membranes of Rhodopseudomonas sphaeroides. V. Identification of bacteriochlorophyll alpha-depleted cytoplasmic membrane in phototrophically grown cells

The separation of membrane fragments was investigated in extracts of phototropically grown Rhodopseudomonas sphaeroides to determine if the plasma membrane contains discrete regions. A highly purified fraction of bacteriochlorophyll alpha-deficient membrane fragments was isolated by differential centrifugation, chromatography on Sepharose 2B, reaggregation, and isopycnic sedimentation on sucrose gradients. Significant levels of b- and c-type cytochromes and succinate dehydrogenase were demonstrated in the isolated membrane fragments and their appearance in electron micrographs, their polypeptide profile in dodecyl sulfate-polyacrylamide gel electrophoresis, and overall chemical composition were essentially identical to a similar fraction isolated from aerobically grown cells. Their polypeptide profiles were distinct from those of the intracytoplasmic chromatophore and outer membranes, and on the basis of bacteriochlorophyll content the phototrophic fraction was contaminated with chromatophores by less than 9%. The membrane fragments contained no diaminopimelic acid or glucosamine. It is condluded that the membrane fragments isolated from phototrophically growing Rp. sphaeroides have arisen from photosynthetic pigment-depleted regions of the plasma membrane structurally and functionally differentiated from the intracytoplasmic chromatophore membrane. These regions represent conserved chemotrophic cytoplasmic membrane whose synthesis continues under photoheterotrophic conditions.

Intracellular location of flexirubins in Flexibacter elegans (Cytophagales)

The inner and outer membranes of 2 strains of Gram-negative Flexibacter elegans, Fx e1 and Fx 3/4, could be separated on sucrose density gradients after the cells had been converted into spheroplasts, and the spheroplasts had been lysed in presence of EDTA and the detergent Brij 58. The light fraction (rho = 1.14 g . cm-3) contained the components of the respiratory chain in high concentrations, but only low amounts of the lipopolysaccharide component, 2-keto-3-deoxyoctonic acid, and was thus mainly material from the inner membrane. The heavy fraction (rho = 1.175 g . cm-3) contained only traces of respiratory chain enzymes, but the majority of the 2-keto-3-deoxyoctonic acid, and was thus mainly material from the outer membrane. The flexirubin pigments were found almost quantitatively in the latter fraction. Strain Fx 3/4 produced carotenoids in addition to flexirubins; in this case the flexirubins were located in the outer, and the carotenoids in the inner membrane.

Proteins exposed at the surface of chromatophores of Rhodospirillum rubrum: the orientation of isolated chromatophores

The exposure of proteins at the surface of isolated chromatophores (i.e., the cytoplasmic face of intracytoplasmic membranes) of Rhodospirillum rubrum was studied by proteolysis as well as by enzymatic iodination with 125I. Analyses were performed after polyacrylamide gel electrophoresis of chromatophore proteins solubilized with sodium dodecyl sulfate. Reversible light induced proton uptake by partially digested chromatophores was used as a criterion for the integrity of the permeability barrier and thus, as evidence for proteolysis only of proteins outside of this barrier. Trypsin or alpha-chymotrypsin completely cleaved four proteins which were identified as the heavy subunit of succinate dehydrogenase (Mr = 64 000), the alpha- and beta-subunits of coupling factor ATPase (Mr = 55 000 and 51 000), and the heavy (H) subunit of photochemical reaction centers (Mr = 31 000). alpha-Chymotrypsin, in addition, attacked the protein (Mr = 9000) of light harvesting bacteriochlorophyll preparations. By enzymatic iodination, the same proteins were labeled as were digested with trypsin or alpha-chymotrypsin except for the protein of Mr = 9000. In addition, significant label was incorporated into three more proteins, one of which (Mr = 41 000) could be identified as a major protein of the cell wall. The complete cleavage with trypsin of four proteins exposed at the surface indicated that isolated chromatophores were homogeneously oriented regardless of the method employed for cell breakage, i.e., passage through a French pressure cell at different forces or osmotic shock of sphaeroplasts.

Isolation and characterization of light harvesting bacteriochlorophyll.protein complexes from Rhodopseudomonas capsulata

The isolation of two native light harvesting bacteriochlorophyl.protein complexes from Rhodopseudomonas capsulata is described. The light harvesting bacteriochlorophyll I (B 875) has been isolated from the blue-green mutant A1a+ lacking both carotenoids and light harvesting bacteriochlorophyll II. Light harvesting bacteriochlorophyll I is associated with a protein (light harvesting band 2) of 12 000 molecular weight. Light harvesting bacteriochlorophyll II complex has been isolated from the mutant Y5 lacking a reaction center and light harvesting bacteriochlorophyll I. Light harvesting bacteriochlorphyll II (B 800 + 850) together with carotenoids is associated with two polypeptides (light harvesting bands 3 and 4) having molecular weights of about 8000 and 10 000 (sodium dodecyl sulfate polyacrylamide gel electrophoresis). A third protein (light harvesting band 1) is in the purified light harvesting II fraction (mol. wt. approx. 14 000), but not associated with bacteriochlorophyll or carotenoids. The amino acid composition of the 3 antenna pigment II proteins is given. The polarity of these proteins was found to be 48%. From the amino acid composition the following molecular weights were calculated band 1: 17 350, band 3: 13 350 and band 4: 10 500.

The early formation of the photosynthetic apparatus in Rhodospirillum rubrum

The time dependent assembly of the photosynthetic apparatus was studied in Rhodospirillum rubrum after transfer of cells growing aerobically in the dark to low aeration. While bacteriochlorophyll (Bchl) cellular levels increase continuously levels of soluble cytochrome C2 do not change significantly. Absorption spectra of membranes isolated at different times after transfer reveal that incorporation of carotenoids lags behind incorporation of Bchl. However, a carotenoid fraction exhibiting spectral properties of spirilloxanthin isomers was isolated apart from membranes. This carotenoid fraction even was present in homogenates from Bchl-free, aerobically grown cells. Incorporation of U-14C-proteinhydrolyzate into membrane proteins showed that proteins are mainly formed which are specific for photosynthetic membranes. Although the proportion of reaction center (RC) Bchl per light harvesting (LH) Bchl does not change the proportions of membrane proteins present in RC and LH preparations change initially. But later on the proportions of the different proteins also reach constant values. Concerning proteins characteristic for cytoplasmic membranes a differential incorporation of label can be observed. The data indicate that the photosynthetic apparatus in Rhodospirillum rubrum is assembled through a sequential mechanism.

Early formation of intracytoplasmic membranes in Rhodospillum rubrum

Cytoplasmic and intracytoplasmic membranes were isolated from Rhodospirillum rubrum by equilibrium sucrose density gradient centrifugation. Immediately after the induction of photosynthetically active intracytoplasmic membranes, bacteriochlorophyll is incorporated predominantly into the cytoplasmic membrane. With increasing pigment concentrations the newly arising intracytoplasmic membranes become sites of preferential bacteriochlorophyll incorporation. During this process the infrared absorption band of the pigment shows a red shift. The shift is more pronounced with intracytoplasmic than with cytoplasmic membranes. Pulse-chase of cytoplasmic membrane proteins reveals that such proteins become constituents of intracytoplasmic membranes.

Membranes of Rhodospirillum rubrum: isolation and physicochemical properties of membranes from aerobically grown cells

Highly purified preparations of cytoplasmic and outer membrane were isolated from aerobically grown Rhodospirillum rubrum lysed by sequential treatment with lysozyme, ethylenediaminetetraacetate, and Brij 58. The membranes were resolved and separated from other cellular constitutents by a combination of velocity and isopyknic sedimentation in sucrose density gradients. On the basis of their appearance in electron micrographs and their protein profiles in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, these preparations appear to be quite similar to those obtained from other gram-negative bacteria. The cytoplasmic membrane fraction contained the majority of the total membrane-bound succinic dehydrogenase activity and was 10-fold enriched in b- and c-type cytochrome with respect to the outer membrane. The latter fraction was characterized by a much greater carbohydrate content and the presence of arachidic acid, which is typical of R. rubrum lipopolysaccharide. Their protein fatty acid, and overall chemical compositions suggested that these preparations were freer from cross-contamination than those obtained from R. rubrum with currently available methods.