Genomic complexity among strains of the facultative photoheterotrophic bacterium Rhodobacter sphaeroides

Pulsed-field gel electrophoresis following the use of rare cutting restriction endonucleases together with Southern hybridization, using markers distributed on chromosomes I and II of Rhodobacter sphaeroides 2.4.1, has been used to examine approximately 25 strains of R. sphaeroides in an effort to assess the occurrence of genome complexity in these strains. The results suggest that genome complexity is widespread and is accompanied by substantial genomic heterogeneity.

A bacteriophage of Rhodopseudomonas blastica

A bacteriophage, øBHG1, was isolated from a small eutrophic pond from which its host, Rhodopseudomonas blastica, was originally obtained. It is a lytic bacteriophage specific for R. blastica which also causes non-specific lysis of Rhodobacter sphaeroides 8253. øBHG1 has an icosahedral head of 62 nm diameter and a short 39 nm tail. Caesium chloride density gradient centrifugation of infected cell lysates gave a single bacteriophage band at a density of 1.385 g cm^-3, but also occasionally a second band was observed at a lower density. No differences were apparent between bacteriophage taken from either of the two bands. øBHG1 contained double-stranded DNA with a size of 48 kb and a G + C content of 50.6 mol%. The bacteriophage adsorbed to both photosynthetically and chemoheterotrophically grown R. blastica at an identical rate of 1.39 × 10^-9 ml^-1 min^-1. One-step growth curves and kinetic studies of the bacteriophage under these physiological regimes showed no differences in the latent and rise periods and only slight changes in the burst size. Adsorption of this bacteriophage is cell-surface specific and attachment only occurs to the 'older' pole of the budding reproductive cell.

A microbiologist's odyssey: Bacterial viruses to photosynthetic bacteria

Perspective can be defined as the relationships or relative importance of facts or matters from any special point of view. Thus, my Personal perspective reflects the threads I followed in a 50-year journey of research in the complex tapestry of bioenergetics and various aspects of microbial metabolism. An early interest in biochemical and microbial evolution led to the fertile hunting grounds of anoxygenic photosynthetic bacteria. Viewed as a physiological class, these organisms show remarkable metabolic versatility in that certain individual species are capable of using all the known major types of energy conversion (photosynthetic, respiratory, and fermentative) to support growth. Since such anoxyphototrophs are readily amenable to molecular genetic/biological manipulation, it can be expected that they will eventually provide important clues for unraveling the evolutionary relationships of the several kinds of energy conversion. I gradually came to believe that understanding the evolution of phototrophs would require detailed knowledge not only of how light is converted to chemical energy, but also of a) pathways of monomer production from extracellular sources of carbon and nitrogen and b) mechanisms cells use for integrating ATP regeneration with the energy-requiring biosyntheses of biological macromolecules. Serendipic observation of photoproduction of H2 from organic compounds by Rhodospirillum rubrum in 1949 led to discovery of N2 fixation by anoxyphototrophs, and this capacity was later exploited for the isolation of hitherto unknown species of photosynthetic prokaryotes, including the heliobacteria. Recent studies on the reaction centers of the heliobacteria suggest the possibility that these bacteria are descendents of early phototrophs that gave rise to oxygenic photosynthetic organisms.

Susceptibility of Rhodobacter sphaeroides to beta-lactam antibiotics: isolation and characterization of a periplasmic beta-lactamase (cephalosporinase)

Thirteen strains of the gram-negative, facultative phototrophic bacterium Rhodobacter sphaeroides were examined fro susceptibility to beta-lactam antibiotics. All strains were sensitive to the semisynthetic penicillins ampicillin, carbenicillin, oxacillin, cloxacillin, and methicillin, but 10 of the 13 strains were resistant to penicillin G, as well as a number of cephalosporins, such as cephalothin, cephapirin, and cephalosporin C. A beta-lactamase (EC 3.5.2.6) with strong cephalosporinase activity was detected in all of the resistant strains of R. sphaeroides. With strain Y-1 as a model, it was shown that the beta-lactamase was inducible by penicillin G, cephalosporin C, cephalothin, and to some minor extent, cephapirin. The beta-lactamase was located in the periplasmic space, from which it could be extracted by osmotic shock disruption. By using this fraction, the beta-lactamase was purified 34-fold to homogeneity by steps involving batch adsorption to and elution from DEAE-Sephadex A50, chromatography on Q-Sepharose, and preparative polyacrylamide gel electrophoresis. The molecular masses of the native and denatured enzymes were determined to be 38.5 kilodaltons by gel filtration and 40.5 kilodaltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively, indicating a monomeric structure. The isoelectric point was estimated to be at pH 4.3. In Tris hydrochloride buffer, optimum enzyme activity was measured at pH 8.5. The beta-lactamase showed high activity in the presence of the substrates cephalothin, cephapirin, cephalosporin C, and penicillin G, for which the apparent Km values were 144, 100, 65, and 110 microM, respectively. Cephalexin, cepharidine, and cephaloridine were poor substrates. The beta-lactamase was strongly inhibited by cloxacillin and oxacillin but only slightly inhibited by phenylmethylsulfonyl fluoride or thiol reagents such as iodoacetate and p-chloromercuribenzoate.