Genome sequence of Halobacterium species NRC-1.

We report the complete sequence of an extreme halophile, Halobacterium sp. NRC-1, harboring a dynamic 2,571,010-bp genome containing 91 insertion sequences representing 12 families and organized into a large chromosome and 2 related minichromosomes. The Halobacterium NRC-1 genome codes for 2,630 predicted proteins, 36% of which are unrelated to any previously reported. Analysis of the genome sequence shows the presence of pathways for uptake and utilization of amino acids, active sodium-proton antiporter and potassium uptake systems, sophisticated photosensory and signal transduction pathways, and DNA replication, transcription, and translation systems resembling more complex eukaryotic organisms. Whole proteome comparisons show the definite archaeal nature of this halophile with additional similarities to the Gram-positive Bacillus subtilis and other bacteria. The ease of culturing Halobacterium and the availability of methods for its genetic manipulation in the laboratory, including construction of gene knockouts and replacements, indicate this halophile can serve as an excellent model system among the archaea.

A fusion inhibitor (FP-21399) for the treatment of human immunodeficiency virus infection: a phase I study.

FP-21399 is a bis(disulfonaphthalene) derivative that prevents human immunodeficiency virus (HIV) infection of uninfected cells by blocking entry of the virus. FP-21399 shows an affinity for lymph nodes. In this phase I study, FP-21399 was administered intravenously over 1 h as a single dose (0.9, 1.7, 2.8, and 4.2 mg/kg) or as a once-weekly infusion (1, 2, and 3 mg/kg) for 4 consecutive weeks to 34 HIV-1 infected patients with CD4(+) cell counts of 50-400 cells/microL. Concomitant antiretroviral therapy was permitted but not required. The most frequent adverse events involved the transient, dose-dependent appearance of drug- or metabolite-related color in the urine and skin. Plasma drug levels were linear with dose. The drug was cleared, with an elimination half-life of 4 h and a terminal half-life of 1.5-2 days; the terminal half-life represented redistribution and clearance from tissues. FP-21399 administered weekly for 4 weeks was well tolerated. Further studies are necessary to define the role of this fusion inhibitor in the treatment of HIV infection.

Photocytotoxicity of curcumin.

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-diene-3,5-dione, is a yellow-orange dye derived from the rhizome of the plant Curcuma longa. Curcumin has demonstrated phototoxicity to several species of bacteria under aerobic conditions (Dahl, T. A., et al., 1989, Arch. Microbiol. 151 183), denoting photodynamic inactivation. We have now found that curcumin is also phototoxic to mammalian cells, using a rat basophilic leukemia cell model, and that this phototoxicity again requires the presence of oxygen. The spectral and photochemical properties of curcumin vary with environment, resulting in the potential for multiple or alternate pathways for the exertion of photodynamic effects. For example, curcumin photogenerates singlet oxygen and reduced forms of molecular oxygen under several conditions relevant to cellular environments. In addition, we detected carbon-centered radicals, which may lead to oxidation products (see accompanying paper). Such products may be important reactants in curcumin's phototoxicity since singlet oxygen and reduced oxygen species alone could not explain the biological results, such as the relatively long lifetime (t1/2 = 27 s) of the toxicant responsible for decreased cell viability.

Spectral and photochemical properties of curcumin.

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a natural yellow-orange dye derived from the rhizome of Curcuma longa, an East Indian plant. In order to understand the photobiology of curcumin better we have studied the spectral and photochemical properties of both curcumin and 4-(4-hydroxy-3-methoxy-phenyl)-3-buten-2-one (hC, half curcumin) in different solvents. In toluene, the absorption spectrum of curcumin contains some structure, which disappears in more polar solvents, e.g. ethanol, acetonitrile. Curcumin fluorescence is a broad band in acetonitrile (lambda max = 524 nm), ethanol (lambda max = 549 nm) or micellar solution (lambda max = 557 nm) but has some structure in toluene (lambda max = 460, 488 nm). The fluorescence quantum yield of curcumin is low in sodium dodecyl sulfate (SDS) solution (phi = 0.011) but higher in acetonitrile (phi = 0.104). Curcumin produced singlet oxygen upon irradiation (lambda > 400 nm) in toluene or acetonitrile (phi = 0.11 for 50 microM curcumin); in acetonitrile curcumin also quenched 1O2 (kq = 7 x 10(6) M-1 s-1). Singlet oxygen production was about 10 times lower in alcohols and was hardly detectable when curcumin was solubilized in a D2O micellar solution of Triton X-100. In SDS micelles containing curcumin no singlet oxygen phosphorescence could be observed. Curcumin photogenerates superoxide in toluene and ethanol, which was detected using the electron paramagnetic resonance/spin-trapping technique with 5,5-dimethyl-pyrroline-N-oxide as a trapping agent. Unidentified carbon-centered radicals were also detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct exposure of mammalian cells to pure exogenous singlet oxygen (1 delta gO2).

Mammalian cells attached to membrane filters or deposited on filters without attachment were exposed to gas-phase singlet oxygen (1O2) in the absence of any other reactants. Cells were exposed in a monolayer or less, in the absence of external medium, during steady-state 1O2 generation, ensuring that singlet oxygen impinged directly and equally on all cells simultaneously. The current methodology for cell exposure ensures that 1O2 is initially the only reactive species to which the cells are exposed. Results seen with this system can therefore be attributed solely and unambiguously to events initiated by 1O2. Further, all cells in the sample receive the same magnitude of exposure per surface area per time interval, which supports calculations of the amount of 1O2 required for irreversible cell damage, based on measured 1O2 flux and exposed cell surface area. Exposure to pure 1O2 irreversibly damaged a variety of cell types, including rat basophilic leukemia, human squamous carcinoma and Chinese hamster lung fibroblast cell lines, and murine primary hepatocytes. Cell survival curves following exposure to 1O2 followed apparent first-order kinetics. A large number of singlet oxygen collisions (approximately 10(12)-10(13) were required to inactivate a cell, on average, indicating a low probability that singlet oxygen collision will reduce cell survival. Regardless of cell type or the survival endpoint measured, lethal toxicity required a fairly constant number of 1O2 collisions per cell. This poses a serious caveat in the assignment of causality in correlating 1O2-initiated cellular damage with mechanism of death, i.e. most damage observed will not be related to death.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotoxicity of volatile and secondary reactive oxygen species generated by photosensitization.

Reactive oxygen species were generated in the gas phase by photosensitization involving illumination of Rose Bengal. Depending on whether the chromophore is dry or solubilized, this system produces either energy-transfer reactions leading to generation of singlet oxygen specifically, or a combination of energy-transfer and electron-transfer reactions, providing both singlet oxygen and reduced forms of oxygen, such as superoxide anion and hydrogen peroxide. In neither case were the reactive species mutagenic in strain TA104 of Salmonella typhimurium, which had been previously shown to be reverted by oxygen species generated by the hypoxanthine-xanthine oxidase system in aqueous medium. However, mixed oxygen species induced an increased lethality in a variety of DNA repair-deficient Escherichia coli strains. This genotoxic effect, mainly reparable by the uvrA and recA mechanisms, was efficiently prevented by the thiol N-acetyl-L-cysteine. Singlet oxygen itself failed to exert direct genotoxic effects, although secondary reactants produced by its reaction with cell components enhanced lethality in some repair-deficient bacteria. Distance-dependence analyses provided measurements of the lifetimes of the oxygen species generated in the gas phase.

Biological inactivation by singlet oxygen: distinguishing O2(1 delta g) and O2(1 sigma g+)

Experiments were performed to determine whether bacterial inactivation in the separated-surface-sensitizer system for singlet oxygen generation is due to O2(1 delta g) or O2(1 sigma g+). The rates of inactivation of Gram-negative Salmonella typhimurium LT-2 and a nonpigmented strain of Gram-positive Sarcina lutea were found to increase linearly with the concentration of 1 delta g. The gas phase lifetime of the inactivating agent was found to be within the range of values expected for the gas phase lifetime of 1 delta g rather than 1 sigma g+. These measurements conclusively demonstrate that bacterial inactivation in this system is due predominantly to 1 delta g. Therefore, studies of bacterial inactivation with this singlet oxygen generating system can be used to assess the role of singlet oxygen in various biological and medically relevant situations.

Readily available fluorescein isothiocyanate-conjugated antibodies can be easily converted into targeted phototoxic agents for antibacterial, antiviral, and anticancer therapy.

Fluorescein-labeled antibodies have little, if any, photodynamic effect because energy acquired by light absorption is rapidly dissipated in fluorescence. However, they can be easily and efficiently converted to selective photodynamic sensitizers by iodination under mild conditions. We have outlined general experimental procedures that can be used to turn a fluorescein-labeled anti-Escherichia coli antibody into a photodynamic sensitizer that selectively kills E. coli while sparing closely related Salmonella typhimurium. These results demonstrate that iodination did not destroy the specificity or activity of the antibody. This technique should be applicable to the large number of fluoresceinated antibodies that are commercially available. Thus, this strategy provides a simple way to rapidly prepare a large number of targeted phototoxic agents that can be used for the selective destruction with light of nearly any type of tissue or organism.

Partition of rose bengal anion from aqueous medium into a lipophilic environment in the cell envelope of Salmonella typhimurium: implications for cell-type targeting in photodynamic therapy.

Photodynamic therapy employs photosensitizers for the selective destruction of tumor tissue while sparing the surrounding healthy tissue. Photosensitization may also be applied to the selective eradication of microorganisms. Photosensitized inactivation requires that the sensitizer bind to the target and therefore the factors that determine photosensitizer binding are critical to photosensitization selectivity. This paper reports the determination of some features of the binding site of the potent photosensitizer, Rose Bengal, in Salmonella bacteria and describes some of the factors that affect this binding. The shift in the wavelength of maximum fluorescence and experiments with the fluorescence quencher TNBS indicate that Rose Bengal is located in a non-aqueous compartment such as the outer membrane. The dye does not seem to significantly accumulate inside the cell, but rather to accumulate in the outer membrane. Time-dependent changes in sensitizer localization in two strains of Salmonella typhimurium that differ in cell wall formation, LT-2 and TA1975, correspond to their differences in susceptibility to photosensitized killing. Therefore these results provide clues to the factors that determine photosensitization selectivity. Understanding this phenomenon is essential for the efficient design of selective photosensitizers and for optimizing antitumor and antiviral photodynamic therapy.

Singlet oxygen induced mutagenesis of benzo[a]pyrene derivatives.

Singlet oxygen activates the mutagenicity of several benzo[a]pyrene (BP) derivatives in the absence of mammalian metabolic action. This has been demonstrated using a separated-surface-sensitizer system for generating chemically pure singlet oxygen, eliminating most of the complications that arise with singlet oxygen generation by conventional photosensitization. Salmonella typhimurium bacteria were exposed to singlet oxygen in the presence of certain BP derivatives and the mutation frequency determined with an azaguanine forward mutation assay. The mutation frequency was increased by exposure to singlet oxygen compared to light-only controls for those BP derivatives that were saturated at either the 7,8 or 9,10 positions but not both. The increase in mutation frequency depends on both the concentration of BP derivative and on the dose of singlet oxygen. Mutation frequency was also significantly increased when bacteria were treated with a solution of trans-7,8-dihydrodiol-BP that had been separately exposed to singlet oxygen, unequivocally demonstrating that the mutagenicity is due to the formation of a product of BP derivative oxidation by singlet oxygen and that this product has a lifetime at least on the order of minutes in acetonitrile. The requirement for singlet oxygen rather than some other form of reactive oxygen was confirmed by determination of the gas phase lifetime of the intermediate responsible for activating mutagenicity. This was performed by measuring the dependence of the mutation frequency on the distance separating the sensitizer from the target. This gives a value of 88 +/- 35 ms, which is in excellent agreement with the mean value of 89 ms calculated from previous independent determinations of the gas phase lifetime of singlet oxygen reported in the literature.

Comparison of killing of gram-negative and gram-positive bacteria by pure singlet oxygen.

Gram-negative and gram-positive bacteria were found to display different sensitivities to pure singlet oxygen generated outside of cells. Killing curves for Salmonella typhimurium and Escherichia coli strains were indicative of multihit killing, whereas curves for Sarcina lutea, Staphylococcus aureus, Streptococcus lactis, and Streptococcus faecalis exhibited single-hit kinetics. The S. typhimurium deep rough strain TA1975, which lacks nearly all of the cell wall lipopolysaccharide coat and manifests concomitant enhancement of penetration by some exogenous substances, responded to singlet oxygen with initially faster inactivation than did the S. typhimurium wild-type strain, although the maximum rates of killing appeared to be quite similar. The structure of the cell wall thus plays an important role in susceptibility to singlet oxygen. The outer membrane-lipopolysaccharide portion of the gram-negative cell wall initially protects the bacteria from extracellular singlet oxygen, although it may also serve as a source for secondary reaction products which accentuate the rates of cell killing. S. typhimurium and E. coli strains lacking the cellular antioxidant, glutathione, showed no difference from strains containing glutathione in response to the toxic effects of singlet oxygen. Strains of Sarcina lutea and Staphylococcus aureus that contained carotenoids, however, were far more resistant to singlet oxygen lethality than were both carotenoidless mutants of the same species and other gram-positive species lacking high levels of protective carotenoids.

Photokilling of bacteria by the natural dye curcumin.

Curcumin is a yellow-orange compound derived from the root of Curcuma longa (Zingiberaceae family), that has been used as a medicine, spice and coloring agent. Curcumin has proved nontoxic in a number of cell culture and whole animal studies. Curcumin has, however, been reported to have bactericidal effects at very high concentrations. When illuminated, curcumin exerted potent phototoxic effects in micromolar amounts. Gram-negative bacteria displayed greater resistance to curcumin phototoxicity relative to Gram-positive bacteria. Oxygen was required for curcumin phototoxicity. Curcumin binding to cells was not required for photokilling; the reactive intermediate therefore must be relatively long-lived. The mechanism(s) of curcumin phototoxicity may involve hydrogen peroxide production. Singlet excited oxygen was not detected.

Pure exogenous singlet oxygen: nonmutagenicity in bacteria.

Singlet oxygen (1 delta gO2) is the lowest energy-excited state of molecular oxygen, and more reactive than the triplet ground-state molecule. Although singlet oxygen has been implicated in a variety of biological effects, including reactions with DNA or some of its components, evidence for mutagenesis by singlet oxygen has remained unclear. We have previously described a system for bacterial exposure to pure exogenous singlet oxygen that eliminates ambiguity regarding the identity of the reactive species responsible for observed results. Despite the potent toxicity of pure singlet oxygen for several different strains of bacteria, we have found no evidence for mutagenicity of singlet oxygen in 26 Salmonella typhimurium histidine-auxotrophic strains killed to 35% survival. These strains included a variety of base-pair substitution or frameshift target sequences for reversion, including targets responsive to oxidative damage and targets rich in GC base pairs. Some strains combined histidine mutations with one or more mutations affecting DNA-repair capacity. 4 strains possessing the hisG46 mutation also were not mutated when exposed to dose ranges killing less than 28% and up to 99% of the bacteria. The relative frequency of small inphase deletions was assayed in hisG428 bacteria exposed to single oxygen and found to be the same as the spontaneous level. In addition to lack of induction of mutation in these strains, the 8-azaguanine forward mutation assay yielded no evidence of mutagenesis by singlet oxygen in strains killed to 15% survival. No induction of genetic changes by singlet oxygen was seen in an assay for duplication of approximately 1/3 of the bacterial chromosome. Tests for the ability of singlet oxygen to induce lambda prophage in E. coli K12 also proved negative. These studies collectively indicate that pure singlet oxygen generated outside the bacterial cell does not react significantly with the bacterial chromosome in ways leading to base-pair substitutions, frameshift mutations, small or large deletions, large duplications, or damage that interferes with DNA replication and induces the SOS system.