Intensification of Hydrogen Production by a Co-culture of Syntrophomonas wolfei and Rhodopseudomonas palustris Employing High Concentrations of Butyrate as a Substrate.

The purpose of this study is to present an effective form of developing a sequential dark (DF) and photo (PF) fermentation using volatile fatty acids (VFAs) and nitrogen compounds as bonding components between both metabolic networks of microbial growing in each fermentation. A simultaneous (co-)culture of Syntrophomonas wolfei (with its ability to consume butyrate and produce acetate) and Rhodopseudomonas palustris (that can use the produced acetate as a carbon source) performed a syntrophic metabolism. The former bacteria consumed the acetate/butyrate mixture reducing the butyrate concentration below 2.0 g/L, permitting Rhodopseudomonas palustris to produce hydrogen. Considering that the inoculum composition (Syntrophomonas wolfei/Rhodopseudomonas palustris) and the nitrogen source (yeast extract) define the microbial biomass specific productivity and the butyrate consumption, a response surface methodology defined the best inoculum design and yeast extract (YE) yielding to the highest biomass concentration of 1.1 g/L after 380.00 h. A second culture process (without a nitrogen source) showed the biomass produced in the previous culture process yields to produce a total cumulated hydrogen concentration of 3.4 mmol. This value was not obtained previously with the pure strain Rhodopseudomonas palustris if the culture medium contained butyrate concentration above 2.0 g/L, representing a contribution to the sequential fermentation scheme based on DF and PF.

Enhanced carotenoid production by Rhodopseudomonas palustris ATCC 17001 under low light conditions.

Carotenoids (CD) are biological pigments produced for commercial purposes. Therefore, it is necessary to study and determine the optimal conditions for increased CD production. There is no consensus in the literature about the conditions that increase CD production. Some authors stated that CD will be preferentially produced at low light intensities, at this adverse condition, microorganism will increase CD production as a survival response mechanism to get more energy. Other authors have mentioned that CD concentrations increase as the light intensity supplied increases, to avoid the overexposure of light and in turn photo-inhibition. Additionally, to increase the specific CD production is also necessary to increase the amount of biomass. In this work, the ammonium concentration (high (HAC) and low (LAC)) and the low light (LL) intensity effect on the CD production was evaluated. Data showed that a high CD-specific concentration of 8.8 mg/gcell was obtained by using R. palustris ATCC 17001 under HAC and LL intensity. CD production was similar at HAC and LAC, suggesting that the light intensity has a greater effect on the specific CD concentration than the nitrogen concentration. In general, the results showed a low biomass production compared to the literature, with high CD synthesis.

Performance intensification of a stirred bioreactor for fermentative biohydrogen production.

In this study, the biohydrogen (bioH2) production of a microbial consortium was optimized by adjusting the type and configuration of two impellers, the mixing regimen and the mass transfer process (KLa coefficients). A continuous stirred-tank reactor (CSTR) system, with a nonstandard geometry, was characterized. Two different mixing configurations with either predominant axial (PB4 impeller) or radial pumping (Rushton impeller) were assessed and four different impeller configurations to produce bioH2. The best configuration for an adequate mixing time was determined by an ANOVA analysis. A response surface methodology was also used to fully elucidate the optimal configuration. When the PB4 impellers were placed in best configuration, c/Dt = 0.5, s/Di = 1, the maximum bioH2 productivity obtained was 440 mL L-1 hr-1, with a bioH2 molar yield of 1.8. The second best configuration obtained with the PB4 impellers presented a bioH2 productivity of 407.94 mL L-1 hr-1. The configurations based on Rushton impellers showed a lower bioH2 productivity and bioH2 molar yield of 177.065 mL L-1 hr-1 and 0.71, respectively. The experiments with axial impellers (PB4) showed the lowest KLa coefficient and the highest bioH2 production, suggesting that mixing is more important than KLa for the enhanced production of bioH2.