Effect of ethanol and hydrogen peroxide on poly(3-hydroxybutyrate) biosynthetic pathway in <Emphasis Type="Italic">Cupriavidus necator</Emphasis> H16

Exposition of Cupriavidus necator to ethanol or hydrogen peroxide at the beginning of the stationary phase increases poly(3-hydroxybutyrate) (PHB) yields about 30%. Hydrogen peroxide enhances activity of pentose phosphate pathway that probably consequently increases intracellular ratio NADPH/NADP⁺. This effect leads to stimulation of the flux of acetyl-CoA into PHB biosynthetic pathway and to an increase of enzymatic activities of β-ketothiolase and acetoacetyl-CoA reductase while activity of PHB synthase remains uninfluenced. During ethanol metabolisation, in which alcohol dehydrogenase is involved, acetyl-CoA and reduced coenzymes NAD(P)H are formed. These metabolites could again slightly inhibit TCA cycle while flux of acetyl-CoA into PHB biosynthetic pathway is likely to be supported. As a consequence of TCA cycle inhibition also less free CoA is formed. Similarly with hydrogen peroxide, activities of β-ketothiolase and acetoacetyl-CoA reductase are increased which results in over-production of PHB. Molecular weight of PHB produced under stress conditions was significantly higher as compared to control cultivation. Particular molecular weight values were dependent on stress factor concentrations. This could indicate some interconnection among activities of β-ketothiolase, acetoacetyl-CoA reductase and PHB molecular weight control in vivo.     

Urea Hydrogen Peroxide Reduces the Numbers of Lactobacilli, Nourishes Yeast, and Leaves No Residues in the Ethanol Fermentation

Urea hydrogen peroxide (UHP) at a concentration of 30 to 32 mmol/liter reduced the numbers of five Lactobacillus spp. (Lactobacillus plantarum, L. paracasei, Lactobacillus sp. strain 3, L. rhamnosus, and L. fermentum) from ~10⁷ to ~10² CFU/ml in a 2-h preincubation at 30°C of normal-gravity wheat mash at ~21 g of dissolved solids per ml containing normal levels of suspended grain particles. Fermentation was completed 36 h after inoculation of Saccharomyces cerevisiae in the presence of UHP, even when wheat mash was deliberately contaminated (infected) with L. paracasei at ~10⁷ CFU/ml. There were no significant differences in the maximum ethanol produced between treatments when urea hydrogen peroxide was used to kill the bacteria and controls (in which no bacteria were added). However, the presence of L. paracasei at ~10⁷ CFU/ml without added agent resulted in a 5.84% reduction in the maximum ethanol produced compared to the control. The bactericidal activity of UHP is greatly affected by the presence of particulate matter. In fact, only 2 mmol of urea hydrogen peroxide per liter was required for disinfection when mashes had little or no particulate matter present. No significant differences were observed in the decomposition of hydrogen peroxide in normal-gravity wheat mash at 30°C whether the bactericidal agent was added as H₂O₂ or as urea hydrogen peroxide. NADH peroxidase activity (involved in degrading H₂O₂) increased significantly (P = 0.05) in the presence of 0.75 mM hydrogen peroxide (sublethal level) in all five strains of lactobacilli tested but did not persist in cells regrown in the absence of H₂O₂. H₂O₂-resistant mutants were not expected or found when lethal levels of H₂O₂ or UHP were used. Contaminating lactobacilli can be effectively managed by UHP, a compound which when used at ca. 30 mmol/liter happens to provide near-optimum levels of assimilable nitrogen and oxygen that aid in vigorous fermentation performance by yeast.     

Bioconversion of waste office paper to hydrogen using pretreated rumen fluid inoculum

In this study, a microbial consortium from an acid-treated rumen fluid was used to improve the yields of H₂ production from paper residues in batch reactors. The anaerobic batch reactors, which contained paper and cellulose, were operated under three conditions: (1) 0.5 g paper/L, (2) 2 g paper/L, and (3) 4 g paper/L. Cellulase was added to promote the hydrolysis of paper to soluble sugars. The H₂ yields were 5.51, 4.65, and 3.96 mmol H₂/g COD, respectively, with substrate degradation ranging from 56 to 65.4 %. Butyric acid was the primary soluble metabolite in the three reactors, but pronounced solventogenesis was detected in the reactors incubated with increased paper concentrations (2.0 and 4.0 g/L). A substantial prevalence of Clostridium acetobutylicum (99 % similarity) was observed in the acid-treated rumen fluid, which has been recognized as an efficient H₂-producing strain in addition to ethanol and n-butanol which were also detected in the reactors.     

Alkaline peroxide pretreatment of corn stover: effects of biomass, peroxide, and enzyme loading and composition on yields of glucose and xylose

Background

Pretreatment is a critical step in the conversion of lignocellulose to fermentable sugars. Although many pretreatment processes are currently under investigation, none of them are entirely satisfactory in regard to effectiveness, cost, or environmental impact. The use of hydrogen peroxide at pH 11.5 (alkaline hydrogen peroxide (AHP)) was shown by Gould and coworkers to be an effective pretreatment of grass stovers and other plant materials in the context of animal nutrition and ethanol production. Our earlier experiments indicated that AHP performed well when compared against two other alkaline pretreatments. Here, we explored several key parameters to test the potential of AHP for further improvement relevant to lignocellulosic ethanol production.

Results

The effects of biomass loading, hydrogen peroxide loading, residence time, and pH control were tested in combination with subsequent digestion with a commercial enzyme preparation, optimized mixtures of four commercial enzymes, or optimized synthetic mixtures of pure enzymes. AHP pretreatment was performed at room temperature (23°C) and atmospheric pressure, and after AHP pretreatment the biomass was neutralized with HCl but not washed before enzyme digestion. Standard enzyme digestion conditions were 0.2% glucan loading, 15 mg protein/g glucan, and 48 h digestion at 50°C. Higher pretreatment biomass loadings (10% to 20%) gave higher monomeric glucose (Glc) and xylose (Xyl) yields than the 2% loading used in earlier studies. An H₂O₂ loading of 0.25 g/g biomass was almost as effective as 0.5 g/g, but 0.125 g/g was significantly less effective. Optimized mixtures of four commercial enzymes substantially increased post-AHP-pretreatment enzymatic hydrolysis yields at all H₂O₂ concentrations compared to any single commercial enzyme. At a pretreatment biomass loading of 10% and an H₂O₂ loading of 0.5 g/g biomass, an optimized commercial mixture at total protein loadings of 8 or 15 mg/g glucan gave monomeric Glc yields of 83% or 95%, respectively. Yields of Glc and Xyl after pretreatment at a low hydrogen peroxide loading (0.125 g H₂O₂/g biomass) could be improved by extending the pretreatment residence time to 48 h and readjusting the pH to 11.5 every 6 h during the pretreatment. A Glc yield of 77% was obtained using a pretreatment of 15% biomass loading, 0.125 g H₂O₂/g biomass, and 48 h with pH adjustment, followed by digestion with an optimized commercial enzyme mixture at an enzyme loading of 15 mg protein/g glucan.

Conclusions

Alkaline peroxide is an effective pretreatment for corn stover. Particular advantages are the use of reagents with low environmental impact and avoidance of special reaction chambers. Reasonable yields of monomeric Glc can be obtained at an H₂O₂ concentration one-quarter of that used in previous AHP research. Additional improvements in the AHP process, such as peroxide stabilization, peroxide recycling, and improved pH control, could lead to further improvements in AHP pretreatment.     

Optimization of pretreatment conditions and use of a two-stage fermentation process for the production of ethanol from seaweed, Saccharina japonica

Saccharina japonica (Sea tangle, Dasima), a seaweed, was fermented in order to produce bioethanol after thermal hydrogen peroxide (H₂O₂) hydrolysis pretreatment and enzymatic saccharification. The optimal pretreatment conditions of 1% (v/v) H₂O₂ (28%, Dustan Pure Chemicals Co., Ltd, Ansan, Korea) and 10% (w/v) seaweed slurry at 121°C for 60 min were determined using the Response Surface Method (RSM). A reducing sugar yield of 33.4% (w/w) and a viscosity of 520 cP were obtained. Enzymatic saccharification was then carried out; a monosaccharide concentration of 28.5 g/L with a 40.5% (w/w) theoretical yield was obtained after the addition of 2-mL Celluclast® 1.5L to 100 g/L of seaweed slurry after thermal H₂O₂ hydrolysis. Fermentation of a two-stage ethanol production was carried out using Saccharomyces cerevisiae KCCM 1129 in order to ferment glucose in the first stage, and a high level of mannitol-acclimated Pichia angophorae KCTC 17574 to ferment mannitol in the second stage. Acclimation of yeast effectively slowed the uptake of sugar in ethanol fermentation. The overall ethanol yield from S. japonica after the two-stage fermentation was 9.9 g/L.     

Production of poly-β-hydroxybutyric acid from carbon dioxide by Alcaligenes eutrophus ATCC 17697T

The characteristics of PHB production from carbon dioxide by autotrophic culture of Alcaligenes eutrophus ATCC 17697^T using a recycled gas closed circuit culture system under the condition of oxygen limitation were investigated. Cell concentration increased to more than 60 g/l after 60 h of cultivation, while the PHB concentration reached 36 g/l. PHB accumulation in the oxygen-limited culture was superior than that in an ammonium-deficient culture. The PHB produced was identified as a homopolymer of d-3-hydroxybutyrate by ¹H and ¹³C NMR analysis. The stoichiometry for PHB production from CO₂ under the oxygen limitation condition was indicated to be as follows: 33H₂ + 12O₂ + 4CO₂ → C₄H₆O₂ + 30H₂O. This stoichiometry shows that the hydrogen consumption per one mole of CO₂ for PHB production is larger than that for cell formation.     

Production of green biodegradable plastics of poly(3-hydroxybutyrate) from renewable resources of agricultural residues

This work describes potential opportunities for utilization of agro-industrial residues to produce green biodegradable plastics of poly(3-hydroxybutyrate) (PHB). Wheat straws were examined with good efficacy of carbon substrates using Cupriavidus necator. Production was examined in separate hydrolysis and fermentation (SHF) in the presence and absence of WS hydrolysis enzymes, and in simultaneous saccharification and fermentation (SSF) with enzymes. Results showed that production of PHB in SSF was more efficient in terms of viable cell count, cell dry weight, and PHB production and yield compared to those of SHF and glucose-control cultures. While glucose control experiment produced 4.6 g/L PHB; SSF produced 10.0 g/L compared to 7.1 g/L in SHF when utilizing enzymes during WS hydrolysis. Results showed that most of sugars produced during the hydrolysis were consumed in SHF (~98 %) compared to 89.2 % in SSF. Results also demonstrated that a combination of glucose and xylose can compensate for the excess carbon required for enhancing PHB production by C. necator. However, higher concentration of sugars at the beginning of fermentation in SHF can lead to cell inhibition and consequently catabolite repressions. Accordingly, results demonstrated that the gradual release of sugars in SSF enhanced PHB production. Moreover, the presence of sugars other than glucose and xylose can eliminate PHB degradation in medium of low carbon substrate concentrations in SSF.     

Utilization of oil extracted from spent coffee grounds for sustainable production of polyhydroxyalkanoates

Spent coffee grounds (SCG), an important waste product of the coffee industry, contain approximately 15 wt% of coffee oil. The aim of this work was to investigate the utilization of oil extracted from SCG as a substrate for the production of poly(3-hydroxybutyrate) (PHB) by Cupriavidus necator H16. When compared to other waste/inexpensive oils, the utilization of coffee oil resulted in the highest biomass as well as PHB yields. Since the correlation of PHB yields and the acid value of oil indicated a positive effect of the presence of free fatty acids in oil on PHB production (correlation coefficient R ²?=?0.9058), superior properties of coffee oil can be probably attributed to the high content of free fatty acids which can be simply utilized by the bacteria culture. Employing the fed-batch mode of cultivation, the PHB yields, the PHB content in biomass, the volumetric productivity, and the Y _P/S yield coefficient reached 49.4 g/l, 89.1 wt%, 1.33 g/(l h), and 0.82 g per g of oil, respectively. SCG are annually produced worldwide in extensive amounts and are disposed as solid waste. Hence, the utilization of coffee oil extracted from SCG is likely to improve significantly the economic aspects of PHB production. Moreover, since oil extraction decreased the calorific value of SCG by only about 9 % (from 19.61 to 17.86 MJ/kg), residual SCG after oil extraction can be used as fuel to at least partially cover heat and energy demands of fermentation, which should even improve the economic feasibility of the process.     

Biosynthesis of poly(3-hydroxybutyrate) (PHB) by Cupriavidus necator H16 from jatropha oil as carbon source

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer that can be synthesized through bacterial fermentation. In this study, Cupriavidus necator H16 is used to synthesize PHB by using Jatropha oil as its sole carbon source. Different variables mainly jatropha oil and urea concentrations, and agitation rate were investigated to determine the optimum condition for microbial fermentation in batch culture. Based on the results, the highest cell dry weight and PHB concentrations of 20.1 and 15.5 g/L, respectively, were obtained when 20 g/L of jatropha oil was used. Ethanol was used as external stress factor and the addition of 1.5 % ethanol at 38 h had a positive effect with a high PHB yield of 0.987 g PHB/g jatropha oil. The kinetic studies for cell growth rate and PHB production were conducted and the data were fitted with Logistic and Leudeking–Piret models. The rate constants were evaluated and the theoretical values were in accordance with the experimental data obtained.     

外源H2O2对盐胁迫下小白菜种子萌发和幼苗生理特性的影响

以小白菜"甜脆青"为试材,研究不同浓度（5、10、25、50和100 mmol/L）过氧化氢（H₂O₂）浸种处理对100 mmol/L NaCl胁迫下小白菜（Brassica chinensis L.）种子萌发、幼苗生长及生理特性的影响。结果表明：100 mmol/L NaCl胁迫明显抑制小白菜种子的萌发状况和幼苗生长,发芽势、发芽指数、活力指数及幼苗根和芽长度和鲜重均明显降低,根和芽中CAT的活性及K⁺含量明显受到抑制,渗透调节物质、活性氧和MDA含量显著增加。不同浓度H₂O₂浸种处理提高了NaCl胁迫下小白菜种子发芽势、发芽指数和活力指数,促进小白菜根和芽的生长,增强了NaCl胁迫下根和芽中SOD、CAT和APX的活性及K⁺含量,降低O₂^-·产生速率及H₂O₂和MDA含量,进一步促进脯氨酸和可溶性糖含量的增加,降低体内Na⁺含量。其中以10 mmol/L H₂O₂处理缓解盐胁迫效果最好,明显缓解NaCl胁迫对小白菜种子萌发和幼苗生长的抑制。     

Poly-3-hydroxybutyrate production byAzotobacter chroococcum

Thirty-seven soil isolates and mutants ofAzotobacter chroococcum tested for poly-3-hydroxybutyrate (PHB) production using Sudan black B staining method were found to be positive. One mutant showed a higher number of PHB-producing cells and maximum number of granules per cell. Using 2% glucose and 15 mmol/L ammonium acetate, PHB production was found to be maximum at 36 and 48 h of growth under submerged cultivation and under stationary cultivation, respectively. PHB production was found to be higher on sucrose and commercial sugar (as carbon sources) as compared to glucose and mannitol. As commercial sugar is cheaper than sucrose it was selected as carbon source for PHB production, that being found to be maximum at 1% concentration. Inorganic nitrogen sources seemed to have no stimulatory effect on the production of PHB. However, ammonium acetate (15 mmol/L) was found to be best for PHB production. Peptone (0.2 %) gave a better yield of PHB under both growth conditions. Using all optimized conditions, PHB production was studied in ten selected strains. Two of them were found to be best PHB producers under both growth conditions, one producing 621 and 740 μg/g dry mass under submerged cultivation and under stationary cultivation, respectively, while the second one produced 589 and 733 μg/g.     

Production of lignocellulose-degrading enzymes employing <Emphasis Type="Italic">Fusarium solani</Emphasis> F-552

In this work, capability of Fusarium solani F-552 of producing lignocellulose-degrading enzymes in submerged fermentation was investigated. The enzyme cocktail includes hydrolases (cellulases, xylanases, and proteinases) as well as ligninolytic enzymes: manganese-dependent peroxidase (MnP), lignin peroxidase (LiP), and laccase (Lac). To our knowledge, this is the first report on production of MnP, LiP, and Lac together by one F. solani strain. The enzyme productions were significantly influenced by application of either lignocellulosic material or chemical inducers into the fermentation medium. Among them, corn bran significantly enhanced especially productions of cellulases and xylanases (248 and 170 U/mL, respectively) as compared to control culture (11.7 and 29.2 U/mL, respectively). High MnP activity (9.43 U/mL, control 0.45 U/mL) was observed when (+)-catechin was applied into the medium, the yield of LiP was maximal (33.06 U/mL, control 2.69 U/mL) in gallic acid, and Lac was efficiently induced by, 2,2′-azino-bis-[3-ethyltiazoline-6-sulfonate] (6.74 U/mL, not detected in control). Finally, in order to maximize the ligninolytic enzymes yields, a novel strategy of introduction of mild oxidative stress conditions caused by hydrogen peroxide into the fermentation broth was tested. Hydrogen peroxide significantly increased activities of MnP, LiP, and Lac which may indicate that these enzymes could be partially involved in stress response against H₂O₂. The concentration of H₂O₂ and the time of the stress application were optimized; hence, when 10 mmol/L H₂O₂ was applied at the second and sixth day of cultivation, the MnP, LiP, and Lac yields reached 21.67, 77.42, and 12.04 U/mL, respectively.     

Enhanced production of lutein in heterotrophic Chlorella protothecoides by oxidative stress

The fast growing unicellular green microalgae Chlorella protothecoides has attracted interest as a promising organism for commercial production of a high-value carotenoid, lutein, by heterotrophic fermentation. Effects of two oxidant-forming reactive oxygen species (ROS) on the biomass concentration, and yield and content of lutein in batch culture of heterotrophic Chlorella protothecoides were investigated in this study. The addition of 0.1 mmol/L H₂O₂ and 0.01 mmol/L NaClO plus 0.5 mmol/L Fe²⁺ to the culture led to the generation of ^·OH and enhanced the lutein content from 1.75 to 1.90 and 1.95 mg/g, respectively. The lutein content further increased to 1.98 mg/g when 0.01 mmol/L H₂O₂ and 0.5 mmol/L NaClO were added to generate ¹O₂. The maximum yield of lutein (28.5, 29.8 and 31.4 mg/L) and a high biomass concentration (15.0, 15.3 and 15.9 g/L) were also achieved through the above treatments. The results indicated that 1O2 could promote lutein formation and enhance lutein production in heterotrophic Chlorella protothecoides. Moreover, ¹O₂ produced from the reaction of H₂O₂ and NaClO was more effective in enhancing lutein production and reducing biomass loss than ^·OH from the reaction of H₂O₂ or NaClO plus Fe²⁺. Supported by the National Key Project of Sci & Tech Supporting Programs Funded by Ministry of Science & Technology of China (Grant No. 2006BAD27B03), Sci & Tech Project of Guangzhou (Grant No. 2005Z3-E0331) and Sci & Tech Project of Guangdong (Grant No. 20052050166)     

A feeding strategy for incorporation of canola derived medium-chain-length monomers into the PHA produced by wild-type Cupriavidus necator

The aim of this study was to increase the density of wild type Cupriavidus necator H16 biomass grown on fructose in order to produce sufficient copolymer of short-chain-length (scl) and medium-chain-length (mcl) polyhydroxyalkanoate (PHA) from canola oil for mechanical testing of the PHA. Initial batch cultivation on fructose was followed by exponential feeding of fructose at a predetermined μ to achieve 44.4 g biomass/l containing only 20 % w/w of polyhydroxybutyrate (PHB) with a Y_x/fructose of 0.44 g/g. In a third stage, canola oil was added under N-limited conditions to produce 92 g/l of biomass with 48 % w/w scl–mcl PHA. Using known standards, the PHA composition was confirmed by GC–MS analysis as 99.81 % 3-hydroxybutyrate, 0.06 % 3-hydroxyvalerate, 0.09 % 3-hydroxyhexanoate and 0.04 % 3-hydroxyoctanoate. The melting temperature (179 °C), crystallinity (54 %), tensile stress (25.1 Mpa) and Young’s modulus (698 Mpa) for a PHB standard decreased to 176 °C, 52 %, 19.1 and 443 Mpa respectively for C. necator PHA produced in the 3-stage process.     

Production of PHB from Crude Glycerol

Crude glycerol – a by‐product of the large scale production of diesel oil from rape – is examined for its possible use as a cheap feedstock for the biotechnological synthesis of poly(3‐hydroxybutyrate) (PHB). The glycerol samples of various manufacturers differ in their contamination with salts (NaCl or K₂SO₄), methanol or fatty acids. At high cell density fermentation these pollutants could possibly accumulate to inhibiting concentrations. The bacteria used were Paracoccus denitrificans and Cupriavidus necator JMP 134, which accumulate PHB from pure glycerol to a content of 70 % of cell dry mass. When using crude glycerol containing 5.5 % NaCl, a reduced PHB content of 48 % was observed at a bacterial dry mass of 50 g/L. Furthermore the PHB yield coefficient was reduced, obviously due to osmoregulation. The effect of glycerol contaminated with K₂SO₄ was less pronounced. The molecular weight of PHB produced with P. denitrificans or C. necator from crude glycerol varies between 620000 and 750000 g/mol which allows the processing by common techniques of the polymer industry.     

Photo-protective properties of Lomentaria hakodatensis yendo against ultraviolet B radiation-induced keratinocyte damage

This study aims to investigate the photoprotective properties of a Lomentaria hakodatensis ethanol extract (LHE) against ultraviolet B (UVB) radiation-induced cellular damage in human HaCaT keratinocytes. LHE exhibited scavenging activity against intracellular reactive oxygen species (ROS), which were generated by either hydrogen peroxide (H₂O₂) or UVB radiation. Moreover, LHE scavenged superoxide anion generated by the xanthine/xanthine oxidase system and hydroxyl radical generated by the Fenton reaction (FeSO₄ + H₂O₂). Furthermore, LHE exhibited UVB absorptive properties and attenuated injury to cellular components (e.g., lipids, proteins and DNA), resulting from UVB-induced oxidative stress. In addition, LHE reduced apoptosis in response to UVB, as shown by decreased DNA fragmentation and the formation of apoptotic bodies. These results suggest that LHE protects human keratinocytes against UVB-induced oxidative stress by scavenging ROS and absorbing UVB rays; thereby reducing damage to biological components.     

Hydrogen peroxide-induced astaxanthin biosynthesis and catalase activity in Xanthophyllomyces dendrorhous

Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) in shake-flask cultures was exposed to 10–20 mmol/L H₂O₂ at various culture stages, and the astaxanthin production was significantly increased by H₂O₂ fed at 0 or 24 h (exponential phase), but only slightly at 48 h (near stationary phase). The astaxanthin production was enhanced most significantly with double feeding of 10 mmol/L H₂O₂ at 0 and 24 h, reaching a cellular content of 1.30 mg/g cell and a volumetric yield of 10.4 mg/L, which were 83 and 65% higher, respectively, than those of the control (0.71 mg/g cell and 6.3 mg/L). The intracellular catalase (CAT) activity was also increased after H₂O₂ treatment. The increases in CAT and astaxanthin of cells could be detected within 4 h of H₂O₂ treatment. The increase in the astaxanthin content of cells was concomitant with a notable decrease in the β-carotene content. The older yeast cells at late culture stage (120 h), due perhaps in part to their higher astaxanthin contents, were more tolerant to H₂O₂ toxicity than the younger cells (24 h). No enhancement of the astaxanthin biosynthesis was attained when H₂O₂ was added to the yeast culture together with a sufficient amount of exogenous CAT. The results suggest that astaxanthin biosynthesis in X. dendrorhous can be stimulated by H₂O₂ as an antioxidative response.     

Study of metabolic network of Cupriavidus necator DSM 545 growing on glycerol by applying elementary flux modes and yield space analysis

A metabolic network consisting of 48 reactions was established to describe intracellular processes during growth and poly-3-hydroxybutyrate (PHB) production for Cupriavidus necator DSM 545. Glycerol acted as the sole carbon source during exponential, steady-state cultivation conditions. Elementary flux modes were obtained by the program Metatool and analyzed by using yield space analysis. Four sets of elementary modes were obtained, depending on whether the pair NAD/NADH or FAD/FADH₂ contributes to the reaction of glycerol-3-phosphate dehydrogenase (GLY-3-P DH), and whether 6-phosphogluconate dehydrogenase (6-PG DH) is present or not. Established metabolic network and the related system of equations provide multiple solutions for the simultaneous synthesis of PHB and biomass; this number of solutions can be further increased if NAD/NADH or FAD/FADH₂ were assumed to contribute in the reaction of GLY-3-P DH. As a major outcome, it was demonstrated that experimentally determined yields for biomass and PHB with respect to glycerol fit well to the values obtained in silico when the Entner–Doudoroff pathway (ED) dominates over the glycolytic pathway; this is also the case if the Embden–Meyerhof–Parnas pathway dominates over the ED.     

Hydrogen peroxide is involved in abscisic acid-induced adventitious rooting in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) under drought stress

Abscisic acid (ABA) and hydrogen peroxide (H₂O₂) are important regulatory factors involved in plant development under adversity stress. Here, the involvement of H₂O₂ in ABA-induced adventitious root formation in cucumber (Cucumis sativus L.) under drought stress was determined. The results indicated that exogenous ABA or H₂O₂ promoted adventitious rooting under drought stress, with a maximal biological response at 0.5 μM ABA or 800 μM H₂O₂. The promotive effects of ABA-induced adventitious rooting under drought stress were suppressed by CAT or DPI, suggesting that endogenous H₂O₂ might be involved in ABA-induced adventitious rooting. ABA increased relative water content (RWC), leaf chlorophyll content, chlorophyll fluorescence parameters (Fv/Fm, ΦPS II and qP), water soluble carbohydrate (WSC) and soluble protein content, and peroxidase (POD), polyphenol oxidase (PPO) and indoleacetate oxidase (IAAO) activities, while decreasing transpiration rate. However, the effects of ABA were inhibited by H₂O₂ scavenger CAT. Therefore, H₂O₂ may be involved in ABA-induced adventitious root development under drought stress by stimulating water and chlorophyll content, chlorophyll fluorescence, carbohydrate and nitrogen content, as well as some enzyme activities.