Many bacteria secrete secondary metabolites, whose production is decoupled from active growth in laboratory cultures. Historically, the advantages of secondary metabolite production have mostly been explored in the context of cellular interactions, such as antibiotic effects on competing organisms, damage caused to host tissues during infection, or cell density-dependent signaling. However, recent studies in the opportunistic pathogen Pseudomonas aeruginosa have brought into focus the physiological effects of secondary metabolites on their producer and their implications for multicellular behavior. P. aeruginosa produces antibiotics called phenazines, which can act as mediators to transfer reducing power to an extracellular oxidant and thereby support bacterial survival when oxygen is not accessible. In the crowded environments of biofilms, communities of bacteria surrounded by self-made matrices, this property of phenazines could support energy generation for cells in anoxic subzones. As biofilm formation is a hallmark of P. aeruginosa colonization at various infection sites within the body, I was motivated to investigate the regulation of phenazine production at the level of synthesis and transport, the distribution of phenazines in P. aeruginosa biofilms, and the effects of individual phenazines on P. aeruginosa gene expression and colony biofilm morphogenesis. As part of this work, a novel electrochemical device was developed that enables direct detection of phenazines released from intact colony biofilms. Application of this device and other electrochemical techniques enabled detection of the reactive phenazine intermediate 5-Me-PCA, which was found to be the primary phenazine affecting P. aeruginosa colony morphogenesis. The production of this phenazine was found to be sufficient for activation of the redox-active transcription factor SoxR and full induction of the RND efflux pump MexGHI-OpmD. Finally, results described in this thesis show that 5-Me-PCA is transported by MexGHI-OpmD, constituting a unique demonstration of the self-protective role of an efflux pump in a gram-negative antibiotic-producing bacterium. These findings raise broad questions about the effects of individual phenazines on biofilm cell physiology and have implications for the contributions of individual phenazines to virulence and survival during infection. The technology developed also has potential applications in novel diagnostic and therapeutic approaches. Chapters 1-3 introduce and highlight advances made in understanding secondary metabolite production, with a focus on P. aeruginosa. Chapter 1 provides an introduction to antibiotic production, the concept of self-resistance and other physiological effects of antibiotics in their producers, and infections caused by P. aeruginosa. Chapter 2 reviews recent studies that have brought into focus the physiological effects of secondary metabolites on their producers and their implications for multicellular behavior. Chapter 3 provides an overview of our current understanding of the regulation of phenazine production in pseudomonads and other bacterial species. Chapter 4 describes the development of an integrated circuit-based platform for detection of redox-active metabolites released from multicellular samples, and demonstrates its application to mapping phenazines released from P. aeruginosa biofilms. The study described in Chapter 5 investigates the role of the P. aeruginosa SoxR regulon, which is induced by phenazines, in phenazine transport and shows that the understudied reactive phenazine 5-methylphenazine-1-carboxylic acid (5-Me-PCA) is transported by the RND efflux pump MexGHI-OpmD and is required for wild-type biofilm formation. Chapter 6 describes the development of an assay for 5-Me-PCA production and studies exploring the role of the regulator PsrA in controlling phenazine biosynthesis. Chapter 7 provides an overview of the findings and open questions to be explored in future research. The P. aeruginosa genome contains two nearly identical operons that encode biosynthetic enzymes for the production of phenazine-1-carboxylic acid, the precursor to all of the other phenazines. The study described in Appendix A characterizes the respective contributions of these operons to phenazine production in shaken liquid cultures and biofilms. Appendix B presents evidence that electron acceptor availability influences, and is influenced by, the morphogenesis of P. aeruginosa colony biofilms. Finally, Appendix C describes a screen for commercially available compounds that inhibit production of the phenazine pyocyanin by P. aeruginosa. Together, these findings reveal the unique physiological roles of specific phenazine-related genetic loci and regulatory proteins and of 5-Me-PCA, a phenazine that was previously overlooked due to the technical challenges associated with its detection. They have also uncovered novel aspects of phenazine production in both shaken liquid cultures and biofilms relevant for the development of therapeutics.

A bacterial biofilm is a community of sessile cells encased in a matrix composed of polysaccharides, proteins, and extracellular DNA that develops according to a reproducible morphogenic program. This morphogenic program is deeply influenced by prevailing redox conditions within the biofilm, which are established by a gradient of terminal electron acceptor through the depth of the biofilm. Terminal electron acceptor limitation leads to redox stress, measured as an elevated ratio of reduced to oxidized forms of the metabolic cofactor nicotinamide adenine dinucleotide, NAD(H). In biofilms of the gram-negative bacterium Pseudomonas aeruginosa, redox stress is relieved by the presence of diffusible redox-cycling molecules, phenazines, that are able to act as an electrical conduit between intracellular NADH and oxygen in the aerobic zone of the biofilm. This is most apparent in the dramatically hyperspread and hyperwrinkled morphologies observed in colony biofilms unable to produce phenazines. However, the ability of phenazines to act as a biologically relevant redox couple between the reducing equivalents of metabolism and atmospheric oxygen also renders them toxic to producing cells. In order to avoid phenazine toxicity, P. aeruginosa encodes self-resistance mechanisms under the control of the redox-sensitive transcription factor SoxR. Two components of the SoxR regulon, the efflux pump MexGHI-OpmD and the monooxygenase PumA, are known to be major contributors to survival in the presence of toxic concentrations of phenazines. This work further details the role of the small protein MexG (Chapter 3) and PumA in phenazine resistance (Chapter 4), and presents an electrochemical platform for studying the effects of a phenazine redox gradient in biofilm morphogenesis (Chapter 5).

Made available in DSpace on 2014-06-11T19:29:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-02Bitstream added on 2014-06-13T19:38:31Z : No. of bitstreams: 1 sudano_mj_me_botfmvz.pdf: 7109768 bytes, checksum: 58bfc3ebf81e7505118cc8f8b907a3a3 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O objetivo deste estudo foi avaliar a suplementação de diferentes concentrações de soro fetal bovino (SFB) e do etossulfato de fenazina (PES), no meio de cultivo durante a produção in vitro (PIV) de embriões bovinos. Em um experimento fatorial 4x3, quatro concentrações de SFB (0%, 2,5%, 5% e 10%), e três períodos de exposição ao PES (Controle, a partir do 60 horas – PES D2,5, e a partir 96 horas – PES D4, de cultivo) foram avaliados sobre o desenvolvimento, acúmulo lipídico, criotolerância, e apoptose celular de embriões frescos e aquecidos. Tomando a fertilização in vitro como referência (D0), no D7 uma amostra dos embriões foi submetida a coloração de Sudan Black B (quantificação do conteúdo lipídico, n=15-60), e a técnica de TUNEL (apoptose, n=15-134). Os demais embriões (n=2647) foram vitrificados, para posterior aquecimento e re-cultivo em SOFaa a 10% de SFB por 12 horas. Passado este período, os embriões aquecidos foram avaliados quanto a re-expansão da blastocele e submetidos a técnica de TUNEL. Para a análise estatística, foi realizada ANOVA seguida do teste de Tukey, ou Kruskal-Wallis seguido do teste de Dunn. Para análise da correlação foi utilizado o teste de correlação linear de Pearson. Foi adotado o nível de significância de 5%. A elevação da suplementação do SFB no meio de cultivo embrionário aumentou (P<0,05) o número de gotas lipídicas citoplasmáticas pequenas, médias e grandes. Além disso, esta elevação do SFB reduziu (P<0,05) a taxa de re-expansão dos embriões vitrificados e aumentou (P<0,05) a taxa de apoptose dos embriões frescos e aquecidos. A adição do PES ao meio de cultivo a partir do D2,5 e a partir do D4 reduziram (P<0,05) o acúmulo lipídico nos embriões bovinos PIV. O uso do PES a partir do D2,5 prejudicou (P<0,05) o desenvolvimento embrionário e não favoreceu (P>0,05) a criotolerância... / The objective of this study was to evaluate the effect of four FCS concentrations and the use of phenazine ethosulfate (PES) in the culture media during in vitro production (IVP) of bovine embryos. In a 4x3 factorial experimental design, four FCS concentrations (0%, 2,5%, 5% and 10%), and three PES exposure periods (control, after 60 hours - PES D2,5, and after 96 hours - PES D4, of embryo culture) were evaluated by embryo development, lipid accumulation, cryotolerance, and fresh and warmed apoptosis. Taking the in vitro fertilization as reference (D0), a sample of D7 embryos was submitted to Sudan Black B stain (lipid content, n=15-60), and to TUNEL reaction (apoptosis, n=15-134). The remaining embryos (n=2647) were vitrified / warmed and re-cultured in SOFaa with 10% of FCS for 12 hours. After this period, re-expansion and warmed apoptosis rate were determined. For statistical analysis, data were tested using ANOVA followed by Tukey´s test, or Kruskal-Wallis followed by Dunn´s test. For correlation analysis Pearson correlation test was used. It was adopted the significance level of 5%. The raise of FCS concentration increased (P<0.05) the number of small, medium and large cytoplasmic lipid droplets. Moreover, this raise of FCS reduced (P<0.05) the re-expansion rate and increased (P<0.05) the fresh and warmed apoptosis rate. The addition of PES in the culture media from D2,5 and D4 reduced (P<0.05) the lipid accumulation. The use of PES from D2,5 affected (P<0.05) embryo development and did not improve (P>0.05) cryotolerance. However, the PES treatment that started at D4 did not affect (P>0.05) embryo development and increased (P<0.05) embryo survival after vitrification. The increase of lipid accumulation had a strong and a moderate correlation with fresh and warmed apoptosis, respectively. However, the fresh apoptosis rate had a very strong correlation with the warmed apoptosis... (Complete abstract, click electronic access below)

Orientador: Fernanda da Cruz Landin e Alvarenga / Banca: Roberto Sartori Filho / Banca: Rui Machado / Resumo: O objetivo deste estudo foi avaliar a suplementação de diferentes concentrações de soro fetal bovino (SFB) e do etossulfato de fenazina (PES), no meio de cultivo durante a produção in vitro (PIV) de embriões bovinos. Em um experimento fatorial 4x3, quatro concentrações de SFB (0%, 2,5%, 5% e 10%), e três períodos de exposição ao PES (Controle, a partir do 60 horas - PES D2,5, e a partir 96 horas - PES D4, de cultivo) foram avaliados sobre o desenvolvimento, acúmulo lipídico, criotolerância, e apoptose celular de embriões frescos e aquecidos. Tomando a fertilização in vitro como referência (D0), no D7 uma amostra dos embriões foi submetida a coloração de Sudan Black B (quantificação do conteúdo lipídico, n=15-60), e a técnica de TUNEL (apoptose, n=15-134). Os demais embriões (n=2647) foram vitrificados, para posterior aquecimento e re-cultivo em SOFaa a 10% de SFB por 12 horas. Passado este período, os embriões aquecidos foram avaliados quanto a re-expansão da blastocele e submetidos a técnica de TUNEL. Para a análise estatística, foi realizada ANOVA seguida do teste de Tukey, ou Kruskal-Wallis seguido do teste de Dunn. Para análise da correlação foi utilizado o teste de correlação linear de Pearson. Foi adotado o nível de significância de 5%. A elevação da suplementação do SFB no meio de cultivo embrionário aumentou (P<0,05) o número de gotas lipídicas citoplasmáticas pequenas, médias e grandes. Além disso, esta elevação do SFB reduziu (P<0,05) a taxa de re-expansão dos embriões vitrificados e aumentou (P<0,05) a taxa de apoptose dos embriões frescos e aquecidos. A adição do PES ao meio de cultivo a partir do D2,5 e a partir do D4 reduziram (P<0,05) o acúmulo lipídico nos embriões bovinos PIV. O uso do PES a partir do D2,5 prejudicou (P<0,05) o desenvolvimento embrionário e não favoreceu (P>0,05) a criotolerância... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The objective of this study was to evaluate the effect of four FCS concentrations and the use of phenazine ethosulfate (PES) in the culture media during in vitro production (IVP) of bovine embryos. In a 4x3 factorial experimental design, four FCS concentrations (0%, 2,5%, 5% and 10%), and three PES exposure periods (control, after 60 hours - PES D2,5, and after 96 hours - PES D4, of embryo culture) were evaluated by embryo development, lipid accumulation, cryotolerance, and fresh and warmed apoptosis. Taking the in vitro fertilization as reference (D0), a sample of D7 embryos was submitted to Sudan Black B stain (lipid content, n=15-60), and to TUNEL reaction (apoptosis, n=15-134). The remaining embryos (n=2647) were vitrified / warmed and re-cultured in SOFaa with 10% of FCS for 12 hours. After this period, re-expansion and warmed apoptosis rate were determined. For statistical analysis, data were tested using ANOVA followed by Tukey's test, or Kruskal-Wallis followed by Dunn's test. For correlation analysis Pearson correlation test was used. It was adopted the significance level of 5%. The raise of FCS concentration increased (P<0.05) the number of small, medium and large cytoplasmic lipid droplets. Moreover, this raise of FCS reduced (P<0.05) the re-expansion rate and increased (P<0.05) the fresh and warmed apoptosis rate. The addition of PES in the culture media from D2,5 and D4 reduced (P<0.05) the lipid accumulation. The use of PES from D2,5 affected (P<0.05) embryo development and did not improve (P>0.05) cryotolerance. However, the PES treatment that started at D4 did not affect (P>0.05) embryo development and increased (P<0.05) embryo survival after vitrification. The increase of lipid accumulation had a strong and a moderate correlation with fresh and warmed apoptosis, respectively. However, the fresh apoptosis rate had a very strong correlation with the warmed apoptosis... (Complete abstract, click electronic access below) / Mestre

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2009. / "August, 2009." Title from electronic dissertation title page (viewed 9/23/2009) Advisor, Stephen Z. D. Cheng; Committee members, Alexei P. Sokolov, Gustavo A. Carri, Darrell H. Reneker, Weiping Zheng; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Les maladies constituent présentement la cause la plus importante de perte économique en aquaculture moderne. Chez certaines espèces, notamment les salmonidés (Oncorhynchus sp. et Salmo sp.), on rapporte des pertes annuelles atteignant cinquante pour cent de la production. À l’heure actuelle, les infections fongiques occupent le second rang derrière les maladies bactériennes en fonction de leur importance économique. Ces poissons sont particulièrement vulnérables à une infection fongique causée par Saprolegnia sp. qui infecte habituellement les oeufs morts. Le saprophyte ubiquitaire se propage ensuite aux oeufs sains et aux individus matures. Malheureusement, le traitement efficace de cette infection, souvent primaire et parfois secondaire, est de plus en plus difficile en raison de nouvelles réglementations restrictives entourant le vert de malachite. Jadis, ce colorant constituait le fongicide le plus efficace dans la lutte contre la saprolégniose, mais son potentiel cancérigène en limite maintenant l’utilisation. Jusqu'à présent, aucun traitement disponible n’est aussi efficace que le vert de malachite pour le contrôle de la saprolégniose. Récemment, nous sommes parvenus à isoler trois bactéries capables d’inhiber la croissance de Saprolegnia sp. in vitro. Ces trois Pseudomonas fluorescens proviennent d’une pisciculture dans laquelle survenaient des cas d’infections à Saprolegnia parasitica. En poussant la caractérisation de l’activité grâce à des analyses de chromatographie liquide haute performance et de spectrométrie de masse, nous avons réussi à isoler et à identifier la molécule responsable. L’acide phénazine-1-carboxylique (PCA), sécrété par deux de nos trois souches, cause l’inhibition de la croissance de Saprolegnia. / Disease is the single largest cause of economic losses in aquaculture, and fungal infections are second only to bacterial diseases in economic importance. Fifty percent per year losses due to fungal infections have been reported in a number of species including salmonids, (Oncorhynchus sp., Salmo sp.) which are particularly susceptible to Saprolegnia sp. The ubiquitous saprophyte commonly infects dead fish eggs and spreads to healthy eggs and fry resulting in a deadly, usually secondary, infection. The ability to effectively treat fungal infections has become increasingly difficult with the accrual of restrictions on the use of the most effective fungicide available, namely malachite green due to concerns regarding its carcinogenicity. Hitherto, no new treatment as effective as malachite green has been available to fish farmers. Recently, we have isolated three Pseudomonas fluorescens bacterial strains, from a Saprolegnia parasitica-infected fish farm, adept at the inhibition of the growth of this oomycete in vitro. The inhibitory activity was found to be present in the culture supernatant of the three strains. Further characterization by high performance liquid chromatography and mass spectrometry has been performed to identify the nature of the inhibition. Phenazine-1-carboxylic acid (PCA), produced by two of the three isolates, was found to be able of inhibiting the growth of Saprolegnia. The causal factor producing inhibition for the third isolate remains a mystery.

Les maladies constituent présentement la cause la plus importante de perte économique en aquaculture moderne. Chez certaines espèces, notamment les salmonidés (Oncorhynchus sp. et Salmo sp.), on rapporte des pertes annuelles atteignant cinquante pour cent de la production. À l’heure actuelle, les infections fongiques occupent le second rang derrière les maladies bactériennes en fonction de leur importance économique. Ces poissons sont particulièrement vulnérables à une infection fongique causée par Saprolegnia sp. qui infecte habituellement les oeufs morts. Le saprophyte ubiquitaire se propage ensuite aux oeufs sains et aux individus matures. Malheureusement, le traitement efficace de cette infection, souvent primaire et parfois secondaire, est de plus en plus difficile en raison de nouvelles réglementations restrictives entourant le vert de malachite. Jadis, ce colorant constituait le fongicide le plus efficace dans la lutte contre la saprolégniose, mais son potentiel cancérigène en limite maintenant l’utilisation. Jusqu'à présent, aucun traitement disponible n’est aussi efficace que le vert de malachite pour le contrôle de la saprolégniose. Récemment, nous sommes parvenus à isoler trois bactéries capables d’inhiber la croissance de Saprolegnia sp. in vitro. Ces trois Pseudomonas fluorescens proviennent d’une pisciculture dans laquelle survenaient des cas d’infections à Saprolegnia parasitica. En poussant la caractérisation de l’activité grâce à des analyses de chromatographie liquide haute performance et de spectrométrie de masse, nous avons réussi à isoler et à identifier la molécule responsable. L’acide phénazine-1-carboxylique (PCA), sécrété par deux de nos trois souches, cause l’inhibition de la croissance de Saprolegnia. / Disease is the single largest cause of economic losses in aquaculture, and fungal infections are second only to bacterial diseases in economic importance. Fifty percent per year losses due to fungal infections have been reported in a number of species including salmonids, (Oncorhynchus sp., Salmo sp.) which are particularly susceptible to Saprolegnia sp. The ubiquitous saprophyte commonly infects dead fish eggs and spreads to healthy eggs and fry resulting in a deadly, usually secondary, infection. The ability to effectively treat fungal infections has become increasingly difficult with the accrual of restrictions on the use of the most effective fungicide available, namely malachite green due to concerns regarding its carcinogenicity. Hitherto, no new treatment as effective as malachite green has been available to fish farmers. Recently, we have isolated three Pseudomonas fluorescens bacterial strains, from a Saprolegnia parasitica-infected fish farm, adept at the inhibition of the growth of this oomycete in vitro. The inhibitory activity was found to be present in the culture supernatant of the three strains. Further characterization by high performance liquid chromatography and mass spectrometry has been performed to identify the nature of the inhibition. Phenazine-1-carboxylic acid (PCA), produced by two of the three isolates, was found to be able of inhibiting the growth of Saprolegnia. The causal factor producing inhibition for the third isolate remains a mystery.

A produção in vitro (PIV) de embriões tem sido utilizada amplamente no Brasil como ferramenta para acelerar o melhoramento genético do rebanho. Quando associada à criopreservação, a PIV permite maior flexibilidade da biotecnologia e possibilita estabelecer um banco de embriões. Há a possibilidade que a alta sensibilidade à criopreservação dos embriões bovinos seja influenciada principalmente pela grande quantidade de lipídeos intracitoplasmáticos, sendo isso relacionado especialmente às condições de cultivo in vitro. O Etossulfato de Fenazina (PES) consiste em um regulador do metabolismo de lipídeos. Através da oxidação de NADPH, estimula a via da pentose-fosfato e assim inibe a síntese de ácidos graxos, podendo levar a efeitos benéficos na criopreservação de embriões bovinos produzidos in vitro. O Fator de transcrição denominado proteína de ligação do elemento regulatório de esterol (SREBP-1c), regula preferencialmente a transcrição de genes da síntese de triacilglicerol e fosfolipídios e, a enzima Estearoil Co-A desaturase (SCD1) promove a síntese de ácidos graxos monoinsaturados, conferindo fluidez às membranas celulares. O objetivo desse trabalho foi avaliar a suplementação de diferentes concentrações do etossulfato de fenazina (PES) no meio de cultivo, durante a produção in vitro de embriões bovinos, e verificar o efeito do PES na taxa de gestação, buscando melhorar a qualidade do embrião para a criopreservação através da redução do acúmulo de lipídeos. Foram avaliadas as taxas de desenvolvimento inicial de embriões produzidos in vitro provenientes de ovários de abatedouro, e as taxas de gestação com o uso de embriões bovinos produzidos in vitro a partir da Aspiração folicular de vacas Holandesas e vitrificados. A análise da expressão de genes relacionados com biossíntese de triacilglicerol, SCD1 e SREBP-1c, teve como finalidade auxiliar nos conhecimentos básicos dos mecanismos de ação do Etossulfato de Fenazina, e foi realizada através de PCR quantitativo em Tempo Real, utilizando pools de cinco embriões para cada grupo. Para a análise estatística, foi realizada ANOVA seguida de teste de médias, e o teste qui-quadrado para as taxas de gestação. Não houve diferença estatística na taxa de clivagem e blastocisto entre o grupo controle e os grupos tratados com 0,2µM; 0,3µM; 0,5µM de PES no meio de cultivo in vitro. A taxa de gestação, utilizando-se embriões criopreservados, transferidos para receptoras, não foi alterada pelo uso de PES. A expressão tanto do SREBP-1c, quanto da SCD1 manteve níveis similares na presença ou ausência de PES durante o cultivo in vitro. Sendo assim faz-se necessário novos estudos para investigar mais detalhadamente o mecanismo de ação do PES nos genes da via de biossíntese de lipídeos e se é viável sua utilização a campo. / The in vitro production (IVP) of embryos has been widely used in Brazil as a tool to accelerate the genetic breeding. When combined with cryopreservation, the IVP allows greater flexibility of biotechnology and enable to establish a bank of embryos. There is a possibility that the greater sensitivity to cryopreservation of bovine embryos is influenced mainly by the large amount of intracytoplasmic lipids, and that is especially related to in vitro culture conditions. The phenazine ethosulfate (PES) consists of a lipid metabolism regulator. By NADPH oxidation, stimulates the pentose-phosphate pathway and thus inhibits the fatty acids synthesis, leading to beneficial effects on cryopreservation of bovine embryos in vitro produced. The transcription factor called sterol regulatory element binding proteins (SREBP-1c), preferably regulates the gene transcription of phospholipids and triacylglycerol synthesis and the stearoyl-Co A desaturase (SCD1) enzyme promotes the monounsaturated fatty acids synthesis, giving fluidity to cell membranes. The aim of this study was to evaluate the supplementation of different concentrations of phenazine ethosulfate (PES) in the culture medium during in vitro production of bovine embryos, and determine the effect of PES in the pregnancy rate, aiming to improve the the embryo quality to cryopreservation by reducing the lipids accumulation. We evaluated the early development rates of in vitro produced embryos and pregnancy rates after inovulation of vitrified in vitro produced embryos derived from the Ovum Pick Up of Holstein cows. Expression analysis of triacylglycerol biosynthesis related genes, SCD1 and SREBP-1c, had the purpose to increase the basic knowledge on phenazine ethosulfate mechanisms of action, and was performed by Quantitative Real-Time PCR using pools of five embryos for each group. For statistical analysis, was performed ANOVA followed by mean test, and the chi-square test for pregnancy rates. There was no statistical difference in the cleavage rate and blastocyst rate between the control group and the groups treated with 0,2µM; 0,3µM; 0,5µM of PES in the medium in vitro culture. The pregnancy rate, using cryopreserved embryos transferred to recipient was not altered by the use of PES. The expression of the SREBP-1c as well as SCD1 remained similar in the presence or absence of the PES during in vitro cultivation. Therefore it is necessary further studies to investigate in more details the PES mechanism of action in the genes of lipid biosynthesis pathway and whether it is feasible to use the field.

<p>The focus of this study is to synthesize a novel hinged polymer actuator. The linking molecule (hinge) is phenazine with interconnected dipyrrole units.</p>

Photodynamic therapy (PDT) is a promising approach used in the treatment of cancer, age related macular degeneration, psoriasis, and other diseases. Our research is focused on the discovery of new photonucleases for use in PDT. This study evaluates the photo-induced DNA cleaving abilities of a series of acridine and phenazine-based chromophores. The extended, aromatic ring systems of these compounds are expected to intercalate between adjoining base pairs in the DNA double-helix. Once irradiated, strand breakage, or nicking of plasmid DNA is achieved at micromolar concentrations of compound (pH 7.0 and 22 °C). Our scavenger experiments show that this process occurs as a result of direct electron transfer to oxygen and/or by means of energy transfer which results in the production of singlet oxygen. Three of the photonucleases being examined were designed to chelate metal. These exhibited increased levels of DNA photocleavage in the presence of copper(II).