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Fermentations of lactose, glucose and galactose using Escherichia coli WDHL, a hydrogen over producer strain, were performed. With glucose as substrate pyruvate was mainly routed to the lactate pathway, resulting in hydrogen production and yield of 1037 mL and 0.30 mol H(2)/mol of glucose, respectively. When galactose was the substrate, the pyruvate formate lyase pathway was the main route for pyruvate and a fermentation yield of 1.12 mol H(2)/mol of galactose and a hydrogen production of 2080 mL were obtained. The fermentation of lactose or glucose plus galactose showed a similar yield of 1.02 mol H(2)/mol of hexose consumed. This work clearly demonstrated that the kinetics of hydrogen and metabolites production as well as the hydrogen yield were affected by the type of sugar used as substrate as reflected by the deviations from the metabolic hydrogen-production pathway., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Abstract: Hydrogen obtained from biomass via dark fermentation is considered a sustainable and clean energy carrier. Batch fermentations with cheese whey powder were performed to assess total hydrogen production (H max), volumetric hydrogen production rate (VHPR), maximum lactose consumption (S max), maximum lactose consumption rate (R max,S), hydrogen molar yield (HMY) and the bacterial species present using two mineral media formulation (A, B). The highest VHPR was 304.8 cm3 dm−3 h−1 and the HMY was 1.8 mol mol−1. Medium B yielded around twice the VHPR than the attained with medium A, but HMY only had a slight increment with the use of medium B. The values reached for S max (17.3 g dm−3), H max (4.863 dm3) and R max,S (2.7 g dm−3 h−1) were also enhanced with medium B. Results suggest that butyrate levels and lower pH are the reasons for diminished hydrogen production with medium A. The microbial communities were analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Only one band was observed in the experiments with medium A, the sequence retrieved from this band presented a closest relative match to the sequence from Citrobacter freundii JCM (100% identity); whereas for medium B, three bands were detected. Sequences from these bands presented high homology to sequences from Clostridium perfringens W11 (95% identity), uncultured Lachnospiraceae bacterium clone MS146A1 E12 (100% identity) and Enterobacter cloacae GH1 (100% identity). From the results obtained it is clear that the formulation of culture media had a strong effect on hydrogen production, kinetics and also on the microbial diversity. [Copyright &y& Elsevier]

Biologically produced hydrogen (biohydrogen) is a valuable gas that is seen as a future energy carrier, since its utilization via combustion or fuel cells produces pure water. Heterotrophic fermentations for biohydrogen production are driven by a wide variety of microorganisms such as strict anaerobes, facultative anaerobes and aerobes kept under anoxic conditions. Substrates such as simple sugars, starch, cellulose, as well as diverse organic waste materials can be used for biohydrogen production. Various bioreactor types have been used and operated under batch and continuous conditions; substantial increases in hydrogen yields have been achieved through optimum design of the bioreactor and fermentation conditions. This review explores the research work carried out in fermentative hydrogen production using organic compounds as substrates. The review also presents the state of the art in novel molecular strategies to improve the hydrogen production. [ABSTRACT FROM AUTHOR]

Abstract: Response surface methodology was applied to optimize the fermentative phase for the mezcal production from Agave salmiana. A 3k factorial design was used to obtain models describing the relationship between the ethanol production, process productivity, and product yield with respect to the fermentation temperature and the initial sugar concentration. The results showed that the fermentative conditions affected the composition of higher alcohols (referred as a quality indicator) in the mezcal as well as the amount of ethanol. The highest ethanol production was attained by employing the following predicted optimum operational conditions: temperature of 28°C and an initial sugar concentration of 105g/l. However, the maximum productivity process was attained with 34.6°C and 90g/l, whereas the maximum product yield and the best quality mezcal at 28°C and 77g/l. Results show that the simultaneous optimization for high ethanol production and fast production rate are not compatible, since high ethanol production requires a high substrate concentration, which in turn inhibit the growth rate. [Copyright &y& Elsevier]

Abstract: Biological hydrogen production is an active research area due to the importance of this gas as an energy carrier and the advantages of using biological systems to produce it. A cheap and practical on-line hydrogen determination is desired in those processes. In this study, an artificial neural network (ANN) was developed to estimate the hydrogen production in fermentative processes. A back propagation neural network (BPNN) of one hidden layer with 12 nodes was selected. The BPNN training was done using the conjugated gradient algorithm and on-line measurements of dissolved CO2, pH and oxidation-reduction potential during the fermentations of cheese whey by Escherichia coli ΔhycA ΔlacI (WDHL) strain with or without pH control. The correlation coefficient between the hydrogen production determined by gas chromatography and the hydrogen production estimated by the BPNN was 0.955. Results showed that the BPNN successfully estimated the hydrogen production using only on-line parameters in genetically modified E. coli fermentations either with or without pH control. This approach could be used for other hydrogen production systems. [ABSTRACT FROM AUTHOR]

In this study, the response surface methodology (RSM) with central composite design (CCD) was employed to improve the hydrogen production by the psychrophilic N92 strain (EU636058) isolated from Antarctica, which is closely related to Pseudorhodobacter sp. (KT163920). The influence of operational conditions such as temperature (4.7–55.2 °C), initial pH (3.44–10.16), and initial glucose concentration (4.7–55.23 g/dm 3 ), as well as the initial concentrations of (NH 4 ) 2 SO 4 (0.05–3.98 g/dm 3 ), FeSO 4 (0.02–1.33 g/dm 3 ) and NaHCO 3 (0.02–3.95 g/dm 3 ) was evaluated. The linear effect of glucose concentration, along with the quadratic effect of all the six factors were the most significant terms affecting the biohydrogen yield by N92 strain. The optimum conditions for the maximum hydrogen yield of 1.7 mol H 2 /mol glucose were initial pH of 6.86, glucose concentration of 28.4 g/dm 3 , temperature 29 °C and initial concentration of (NH 4 ) 2 SO 4 , FeSO 4 and NaHCO 3 of 0.53, 1.55 and 1.64 g/dm 3 respectively. Analysis of the metabolites produced under the optimum conditions showed that the most abundant were acetic acid (0.8 g/dm 3 ), butyric acid (0.7 g/dm 3 ) and ethanol (2.1 g/dm 3 ). We suggest that the bioprocess established in this study using the strain N92 could be an alternative for hydrogen production with the advantages of constituting low energy costs in fermentation. [ABSTRACT FROM AUTHOR]

Abstract: This study reports a fermentative hydrogen production by Escherichia coli using cheese whey as substrate. To improve the biohydrogen production, an E. coli ΔhycA ΔlacI strain (WDHL) was constructed. The absence of hycA and lacI genes had a positive effect on the biohydrogen production. The strain produced 22% more biohydrogen in a shorter time than the wild-type (WT) strain. A Box-Behnken experimental design was used to optimize pH, temperature and substrate concentration. The optimal initial conditions for biohydrogen production by WDHL strain were pH 7.5, 37°C and 20g/L of cheese whey. The specific production rate was improved from 3.29mL H2/optical density at 600nm (OD600nm) unit-h produced by WDHL under non-optimal conditions to 5.88mL H2/OD600nm unit-h under optimal conditions. Using optimal initial conditions, galactose can be metabolized by WDHL strain. The maximum yield obtained was 2.74mol H2/mol lactose consumed, which is comparable with the yield reached in other hydrogen production processes with Clostridium sp. or mixed cultures. [Copyright &y& Elsevier]

Abstract: Due to the renewed interest in finding sustainable fuels or energy carriers, biohydrogen (Bio-H2) from biomass is a promising alternative. Fermentative Bio-H2 production was studied in a continuous stirred tank reactor (CSTR) operated during 65.6d with cheese whey (CW) as substrate. Three hydraulic retention times (HRTs) were tested (10, 6 and 4h) and the highest volumetric hydrogen production rate (VHPR) was attained with HRT of 6h. Therefore, four organic loading rates (OLRs) at a fixed HRT of 6h were tested thereafter, being: 92.4, 115.5, 138.6 and 184.4glactose/L/d. The highest VHPR (46.61mmolH2/L/h) and hydrogen molar yield (HMY) of 2.8molH2/mol lactose were found at an OLR of 138.6glactose/L/d; a sharp fall in VHPR occurred at an OLR of 184.4glactose/L/d. Butyric, propionic and acetic acids were the main soluble metabolites found, with butyric-to-acetic ratios ranging from 1.0 to 2.4. Bacterial community was identified by partial sequence analysis of the 16S rRNA and polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE). The results showed that at HRT of 10h and 6h were dominated by the Clostridium genus. The VHPR attained in this study is the highest reported value for a CSTR system using CW as substrate with anaerobic sludge as inoculum and represents a 33-fold increase compared to a previous study. Thus, it was demonstrated that continuous fermentative Bio-H2 production from CW can be significantly enhanced by an appropriate selection of parameters such as HRT and OLR. Enhancements in VHPR are significant because it is a critical parameter to determine the full-scale practical application of fermentation technologies that will be used for sustainable and clean energy generation. [Copyright &y& Elsevier]