Meral Yücel

Aspects of the metabolism of hydrogen production by Rhodobacter sphaeroides

Abstract Photosynthetic bacteria are favorable candidates for biological hydrogen production due to their high conversion efficiency and versatility in the substrates they can utilize. For large-scale hydrogen production, an integrated view of the overall metabolism is necessary in order to interpret results properly and facilitate experimental design. In this study, a summary of the hydrogen production metabolism of the photosynthetic purple non-sulfur (PNS) bacteria will be presented. Practically all hydrogen production by PNS bacteria occurs under a photoheterotrophic mode of metabolism. Yet results show that under certain conditions, alternative modes of metabolism—e.g. fermentation under light deficiency—are also possible and should be considered in experimental design. Two enzymes are especially critical for hydrogen production. Nitrogenase promotes hydrogen production and uptake hydrogenase consumes hydrogen. Though a wide variety of substrates can be used for growth, only a portion of these is suitable for hydrogen production. The efficiency of a certain substrate depends on factors such as the activity of the TCA cycle, the carbon-to-nitrogen ratio, the reduction-state of that material and the conversion potential of the substrate into alternative metabolites such as PHB. All these individual components of the hydrogen production interact and are subject to strict regulatory controls. An overall scheme for the hydrogen production metabolism is presented.

Antioxidant responses of tolerant and sensitive barley cultivars to boron toxicity

Abstract Effect of boron toxicity on antioxidant response of sensitive (Hamidiye) and tolerant (Anadolu) barley ( Holgarium vulgar ) cultivars was investigated. Eight days old hydroponically grown seedlings were subjected to 5 and 10 mM boric acid treatments for 5 days. Growth parameters (dry-wet weight), protein, proline, MDA, H 2 O 2 contents, membrane damage and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathion reductase (GR) was evaluated in root and shoot tissues. Compared with controls (no boric acid treatment) boron toxicity resulted in a reduction in root weights and did not cause any significant change in protein contents. Boric acid treatment did not cause significant ( P >0.05) changes in proline and H 2 O 2 contents of both tissues and cultivars. On contrary, MDA contents and electrolyte leakage exhibited a dose dependent increase in shoots whereas no significant change was observed in root tissues. Higher extend of membrane damage was observed in leaves of the sensitive cultivar. Total SOD, CAT and GR activities in shoot tissue of both cultivars did not change significantly whereas significantly higher APX activities was observed at 10 mM boric acid treatments. Significant increases in total SOD, CAT and decrease in GR activities was observed in roots of the sensitive cultivar. Roots of resistant cultivar, on contrary, exhibited enhanced CAT and decreased APX activity whereas no significant changes was observed in total SOD and GR activities. Our data suggest that, boron toxicity induced membrane damage in barley leaves, do not involve active oxygen species and antioxidant enzyme activity is not a critical factor in boron toxicity tolerance mechanism. To the best of our knowledge, this is the first report on antioxidant response of barley seedlings under boron toxicity.

Kinetics of biological hydrogen production by the photosynthetic bacterium Rhodobacter sphaeroides O.U. 001

The kinetics and the effects of various parameters on hydrogen production by Rhodobacter sphaeroides O.U. 001 were investigated in a batch column photobioreactor. In particular, the effect of the inoculum age and the implementation of a light–dark cycle illumination scheme for emulating natural sunlight have been investigated in detail. The possibility of using yeast extract to replace the rather expensive vitamin mixture in the medium was also studied. The results show that hydrogen production is decreased when the initially inoculated bacteria have a high culture age. Exposure of the bacterial culture to light–dark cycles increased the amount of hydrogen compared to continuous illumination, all other parameters remaining the same. Similarly, the use of yeast extract to replace the vitamins increased the growth and hydrogen production rates, however, with a slight reduction in the total amount of gas produced and the hydrogen fraction in the evolved gas.

Substrate consumption rates for hydrogen production by Rhodobacter sphaeroides in a column photobioreactor

The effect of l-malic acid and sodium glutamate, which serve as the carbon and nitrogen source, respectively, on hydrogen production by Rhodobacter sphaeroides O.U.001 has been investigated in a batch water jacketed glass column photobioreactor (PBR), which has an inner volume of 400 ml. The PBR was operated at different carbon to nitrogen ratios at 32°C with a tungsten lamp at a light intensity of 200 W m−2. Carbon to nitrogen ratio was found to be an important parameter for bio-hydrogen production. Moreover, hydrogen gas production was dependent on certain threshold concentrations of sodium glutamate. l-malic acid consumption was found to be first order with respect to l-malic acid concentration, whereas sodium glutamate consumption was found to be second order with respect to glutamate concentration. It was concluded that there is a close relationship between the hydrogen production rate and substrate consumption rates. A kinetic model is developed, which relates hydrogen gas production per amount of biomass, l-malic acid, and sodium glutamate concentrations.

Photobiological hydrogen production by using olive mill wastewater as a sole substrate source

Abstract In the present work olive mill wastewater (OMW) collected from West Anatolia—Turkey during 2001, containing 36.02 g carbon, 5.26 g hydrogen, and 0.96 g nitrogen in 100 g suspended solid was used as a sole substrate for the production of hydrogen gas by Rhodobacter sphaeroides O.U.001 in 400 ml glass, column-photobioreactors. Hydrogen production studies on diluted-OMW were investigated in the range of 20% (v/v) and 1% (v/v) OMW containing media. Below 5% OMW containing media, bacterial growth rate fitted well to the logistic model where hydrogen production was observed for the ones below 4% OMW. A maximum hydrogen production potential (HPP) of 13.9 l H 2 / l OMW was obtained at 2% OMW. During the biological hydrogen production process, chemical oxygen demand (COD) of the diluted wastewater decreased from 1100 to 720 mg / l ; biochemical oxygen demand (BOD) decreased from 475 to 200 mg / l , and the total recoverable phenol content (ortho- and meta-substitutions) decreased from 2.32 to 0.93 mg / l . In addition, valuable by-products such as carotenoid (40 mg / l OMW ) and polyhydroxybutyrate (PHB) (60 mg / l OMW ) were obtained. According to these results, OMW was concluded to be a very promising substrate source for biohydrogen production process, with additional benefits of its utilization with regard to environmental and economical aspects.

Antioxidant responses of shoots and roots of lentil to NaCl-salinity stress

The effect of salt stress (100 mM and 200 mM NaCl) on antioxidant responses in shoots and roots of 14-day-old lentil (Lens culinaris M.) seedlings was investigated. Salt stress caused a significant decrease in length, wet-dry weight and an increase in proline content of both shoot and root tissues. In leaf tissues, high salinity treatment resulted in a 4.4 fold increase in H2O2 content which was accompanied by a significant level of lipid peroxidation and an increase in electrolyte leakage. Root tissues were less affected with respect to these parameters. Leaf tissue extracts exhibited four activity bands, of which two were identified as Cu/Zn-SOD and others as Fe-SOD and Mn-SOD. Fe-SOD activity was missing in root extracts. In both tissues Cu/Zn-SOD activity comprised 70–75% of total SOD activity. Salt stress did not cause a significant increase in total SOD activity of leaf tissues but a significant enhancement (88%) was observed in roots mainly due to an enhancement in Cu/ZnSOD isoforms. Compared to leaf tissues a significantly higher constitutive ascorbate peroxidase (APX) and glutathion reductase (GR) activity was observed in root tissues. Upon salt stress no significant change in the activity of APX, catalase (CAT) and GR was observed in root tissues but a higher APX activity was present when compared to leaf tissues. On the other hand, in leaf tissues, with the exception of CAT, salt stress caused significant enhancement in the activity of other antioxidant enzymes. These results suggested that, root tissues of lentil are protected better from NaCl stress induced oxidative damage due to enhanced total SOD activity together with a higher level of APX activity under salinity stress. To our knowledge this is the first report describing antioxidant enzyme activities in lentil.

Photoproduction of hydrogen from sugar refinery wastewater by Rhodobacter sphaeroides O.U. 001

Pretreated sugar refinery wastewater (SRWW) was used for the production of hydrogen by Rhodobacter sphaeroides O.U.001 in a 0.4 l column photobioreactor. Hydrogen was produced at a rate of 0.001 l hydrogen/h/l culture in 20% dilution of SRWW. To adjust the carbon concentration to 70 mM and nitrogen concentration to 2 mM, sucrose or L-malic acid was added as carbon source and sodium glutamate was added as nitrogen source to the 20% dilution of SRWW. By these adjustments, hydrogen production rate was increased to 0.005 l hydrogen/h/l culture. Continuous hydrogen production was achieved in the same medium for 100 days at three different dilution rates. The maximum hydrogen produced was 2.67 l (in 100 days) at a dilution rate of 0.0013 h−1.

Effect of clay pretreatment on photofermentative hydrogen production from olive mill wastewater

The aim of this paper was to gain further insight into the effect of the clay pretreatment process on photofermentative hydrogen production. This two-stage process involved a clay pretreatment step followed by photofermentation which was performed under anaerobic conditions with the illumination by Tungsten lamps. Rhodobacter sphaeroides O.U.001 was used for photofermentation. Higher amounts of color (65%), total phenol (81%) and chemical oxygen demand (31%) removal efficiencies were achieved after clay pretreatment process. During photofermentative hydrogen production with the effluent of clay pretreatment process, the main organic compounds resulting higher hydrogen production rates were found to be acetic, lactic, propionic, and butyric acids. Compared to photofermentation using raw olive mill wastewater ( 16LH2/LOMW), the amount of photofermentative hydrogen production was doubled by using the effluent of the clay pretreatment process (31.5LH2/LOMW). The reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols; minor removal of organic acids, sugars and amino acids that are known to enhance photofermentative hydrogen production; and the color depletion of raw OMW which might cause a shadowing effect on the photosynthetic bacteria.

Identification of by-products in hydrogen producing bacteria; Rhodobacter sphaeroides O.U. 001 grown in the waste water of a sugar refinery

Rhodobacter sphaeroides O.U. 001 is able to produce hydrogen anaerobically upon illumination. The cells were screened for the presence of valuable by-products such as poly-β-hydroxy (PHB) butyric acid aiming to improve the feasibility of the system. Also waste water from a sugar refinery was used for bacterial growth to further increase the feasibility. Under aerobic conditions the standard growth media containing l-malic acid and sodium glutamate in 7.5/10 and 15/2 molar ratios and a medium containing 30% waste water from sugar refinery were used. In this case the maximum concentration of PHB produced were approximately 0.2 g l− 1 in both of the standard media whereas it was 0.3 g l− 1 in medium containing 30% waste water. By using the medium containing 30% waste water, PHB and hydrogen productions were determined under anaerobic conditions. The maximum concentration of PHB produced was around 0.5 g l− 1 and the amount of gas collected was 35 ml in 108 h. From these results it can be concluded that PHB can be collected during hydrogen production. The use of waste water from sugar refinery increased the yield.

Transformation of lentil ( Lens culinaris M.) cotyledonary nodes by vacuum infiltration of Agrobacterium tumefaciens

Lentil cotyledonary nodes are some of the most regenerative tissues in legumes. Attempts to transform them by vacuum filtration have been limitedly successful. This report describes a rapid and convenient transient expression protocol based on vacuum infiltration ofAgrobacterium cells into lentil cotyledonary nodes. Vacuum-infiltrated tissues had significantly (P<.05) higher transient GUS expression than did noninfiltrated tissues. Under optimal conditions (infiltration at 200 mmHg for 20 min), 95% of theAgrobacterium-infiltrated explants exhibited an average of 16 blue foci. We believe this to be the first report of this technique for transient gene expression in lentil cotyledonary nodes.