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Öğe Effect of Light Intensity, Wavelength and Illumination Protocol on Hydrogen Production in Photobioreactors(Bentham Science Publ, 2012) Uyar, Basar; Yucel, Meral; Gunduz, Ufuk; Eroglu, InciPhotofermentative hydrogen production is a bioprocess in which photosynthetic purple nonsulfur bacteria grow heterotrophically on organic acids like acetic acid, lactic acid and butyric acid and produce hydrogen using light energy under anaerobic conditions. Two enzymes are specifically involved in hydrogen production, namely nitrogenase and hydrogenase. While nitrogenases produce hydrogen under nitrogen-limited conditions acting as ATP-dependent hydrogenase, hydrogenases have the ability for both production and consumption of molecular hydrogen depending on the type of hydrogenase and physiological conditions. Photofermentation process can be achieved in a wide variety of conditions such as in batch or continuous mode, upon artificial or solar illumination, utilizing various carbon and nitrogen sources including food industry wastewater and dark fermentation effluents. Panel and tubular photobioreactors are the most applicable bioreactor types since they ensure simple design, reasonable material and production costs and high light energy utilization. Physiological parameters such as pH, temperature, medium composition and light intensity control the yield and hydrogen productivity of the bacteria. Hydrogen productivity and yield can also be increased by using genetically modified bacterial strains or immobilization of bacteria. Genetic studies focus on development of mutant strains by disrupting the uptake hydrogenase genes, altering pigmentation and blocking alternative by-product biosynthesis. Techno-economic evaluations show that photofermentative hydrogen production process is very near to the commercialization stage, however demo scale experience is necessary to solve some problems such as low rate of hydrogen production and the cost associated with photobioreactor scale-up. Furthermore, recent studies are trying to integrate photofermentation to dark fermentation to have an enhanced hydrogen production yield. Finally, the whole process could end up with a fuel cell application where the produced hydrogen is stored for future uses.Öğe Effect of Nerium oleander distillate on MCF-7 breast cancer cell lines(CURRENT BIOLOGY LTD, 2011) Kars, Meltem Demirel; Kars, Gokhan; Gunduz, Ufuk; Uney, Kamil; Bas, Ahmet Levent[Abstract not Available]Öğe Evaluation of hydrogen production by Rhodobacter sphaeroides OU001 and its hupSL deficient mutant using acetate and malate as carbon sources(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Kars, Goekhan; Gunduz, Ufuk; Yucel, Meral; Rakhely, Gabor; Kovacs, Kornel L.; Eroglu, InciRhodobacter sphaeroides O.U.001 is one of the candidates for photobiological hydrogen production among purple non-sulfur bacteria. Hydrogen is produced by Mo-nitrogenase from organic acids such as malate or lactate. A hupSL in frame deletion mutant strain was constructed without using any antibiotic resistance gene. The hydrogen production potential of the R. sphaeroides O.U.001 and its newly constructed hupSL deleted mutant strain in acetate media was evaluated and compared with malate containing media. The hupSL(-) R. sphaeroides produced 2.42 l H-2/l culture and 0.25 l H-2/l culture in 15 mM malate and 30 mM acetate containing media, respectively, as compared to the wild type cells which evolved 1.97 l H-2/l culture and 0.21 l H-2/l culture in malate and acetate containing media, correspondingly. According to the results, hupSL- R. sphaeroides is a better hydrogen producer but acetate alone does not seem to be an efficient carbon source for photo-heterotrophic H-2 production by R. sphaeroides. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.Öğe A microarray based expression profiling of paclitaxel and vincristine resistant MCF-7 cells(ELSEVIER SCIENCE BV, 2011) Kars, Meltem Demirel; Iseri, Ozlem Darcansoy; Gunduz, UfukResistance to the broad spectrum of chemotherapeutic agents in cancer cell lines and tumors has been called multiple drug resistance (MDR). In this study, the molecular mechanisms of resistance to two anticancer agents (paclitaxel and vincristine) in mammary carcinoma cell line MCF-7 were investigated. Drug resistant sublines to paclitaxel (MCF-7/Pac) and vincristine (MCF-7/Vinc) that were developed from sensitive MCF-7 cells (MCF-7/S) were used. cDNA microarray analysis was performed for the RNA samples of sensitive and resistant cells in duplicate experiments. GeneSpring GX 7.3.1 Software was used in data analysis. The results indicated that the upregulation of MDR] gene is the dominating mechanism of the paclitaxel and vincristine drug resistance. Additionally the upregulation of the genes encoding the detoxifying enzymes (i.e. GSTP1) was observed. Significant downregulation of apoptotic genes (i.e. PDCD2/4/6/8) and upregulation of some cell cycle regulatory genes (CDKN2A, CCNA2 etc.) was seen which may be in close relation to MDR in breast cancer. Drug resistant cancer cells exhibit different gene expression patterns depending on drug treatment, and each drug resistance phenotype is probably genetically different. Further functional studies are needed to demonstrate the complete set of genes contributing to the drug resistance phenotype in breast cancer cells. (C) 2011 Elsevier B.V. All rights reserved.Öğe Paclitaxel Resistance in MCF-7/Pac Cell Line is Reversed Successfully by Saikosaponin A and Saikosaponin D(AKAD DOKTORLAR YAYINEVI, 2013) Kars, Meltem D.; Kars, Gokhan; Gunduz, UfukCancer cells demonstrate multiple drug resistance phenotype frequently after chemotherapy. The resistance of cancer cells to various chemotherapeutic agents is defined as multiple drug resistance. The purpose of this study is to investigate the potential reversal effects of active agents, that are found high amount in plants, on resistant MCF-7 cell lines. The effects of potential MDR modulators combined with anticancer drugs were also evaluated. Flow cytometry, fluorescence microscopy and checkerboard combination assays were performed to study the reversal of drug resistance and for investigation of the antiproliferative effects of the combination of anticancer drugs with the modulators. Paclitaxel and potential MDR modulators (verapamil, saikosaponin A, D and isoquercitrin) were applied to the sublines in combination. Fluorescence accumulation levels and fractional inhibitory indices show that saikosaponin A and D are effective MDR reversal agents that may be used together with paclitaxel in drug resistant mammary carcinoma subline. In conclusion this report represents saikosaponin A and D from natural resources are valuable reagents that may improve the success of chemotherapy.Öğe Towards a super H-2 producer: Improvements in photofermentative biohydrogen production by genetic manipulations(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Kars, Goekhan; Gunduz, UfukPhotofermentative hydrogen production by purple non-sulfur bacteria is a potential candidate among biological hydrogen production methods. Hydrogen is produced under anaerobic conditions in light using different organic substrates as carbon source. The hydrogen evolution occurs mainly through the catalytic activity of the nitrogenases under non-repressive concentrations of ammonia. However, total hydrogen production is constrained due to several reasons in purple non-sulfur (PNS) bacteria, such as consumption of hydrogen by uptake hydrogenase, inefficient hydrogen production capacity of nitrogenase, limited electron flow to the nitrogenase, sensitivity of nitrogenase towards ammonia, etc. Hence, PNS bacteria need to be manipulated genetically to overcome these limitations and to make the process practically feasible. This review focuses on various approaches for the genetic improvement of biohydrogen production by PNS bacteria. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
