Optimization of dark fermentative biohydrogen production from rice starch by Enterobacter aerogenes MTCC 2822 and Clostridium acetobutylicum MTCC 11274

Dark fermentative biohydrogen production (DFBHP) has potential for utilization of rice starch wastewater (RSWW) as substrate. The hydrogen production of Enterobacter aerogenes MTCC 2822 and Clostridium acetobutylicum MTCC 11274, in pure culture and co-culture modes, was evaluated. The experiments were performed in a 2 L bioreactor, for a batch time of 120 h. The co-culture system resulted in highest cumulative hydrogen (1.13 L H₂/L media) and highest yield (1.67 mol H₂/mol glucose). Two parameters were optimized through response surface methodology (RSM)-substrate concentration (3.0-5.0 g/L) and initial pH (5.5-7.5), in a three-level factorial design. A total of 11 runs were performed in duplicate, which revealed that 4.0 g/L substrate concentration and 6.5 initial pH were optimal in producing hydrogen. The metabolites produced were acetic, butyric, propionic, lactic and isobutyric acids. The volumetric H₂ productions, without and with pH adjustments, were 1.24 L H₂/L media and 1.45 L H₂/L media, respectively.

Design and engineering of artificial microbial consortia for biohydrogen production

In natural microbial ecosystems the metabolic diversity of the organisms enables interaction among the community members and allows them to engage in syntrophic interactions. With regard to biotechnology, artificial microbial consortium engineering is used to improve productivities and yields of bioprocesses. However, to achieve supreme productivity or efficiency at industrial scale, defined ecosystems must be physiologically well-selected to meet eco-biotechnological demands. Here, we present an artificial microbial consortia design and engineering pipeline for developing dark fermentative biohydrogen production processes. The proposed pipeline might be considered as a blue-print for enhancing other bioprocesses that fundamentally face metabolic restrictions or kinetic limitations.

Advances and Applications of Clostridium Co-culture Systems in Biotechnology

Clostridium spp. are important microorganisms that can degrade complex biomasses such as lignocellulose, which is a widespread and renewable natural resource. Co-culturing Clostridium spp. and other microorganisms is considered to be a promising strategy for utilizing renewable feed stocks and has been widely used in biotechnology to produce bio-fuels and bio-solvents. In this review, we summarize recent progress on the Clostridium co-culture system, including system unique advantages, composition, products, and interaction mechanisms. In addition, biochemical regulation and genetic modifications used to improve the Clostridium co-culture system are also summarized. Finally, future prospects for Clostridium co-culture systems are discussed in light of recent progress, challenges, and trends.

Direct Fermentative Hydrogen Production from Cellulose and Starch with Mesophilic Bacterial Consortia

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H2 consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H2/lmedium) and H2 yield (1.7 mol H2/molhexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H2/lmedium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles - 0.97 mol H2/molhexose (5.93 mmol H2/gcellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H2 production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H2/molhexose).

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H2 consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H2/lmedium) and H2 yield (1.7 mol H2/molhexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H2/lmedium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles – 0.97 mol H2/molhexose (5.93 mmol H2/gcellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H2 production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H2/molhexose).

Environmental applications of chitosan and cellulosic biopolymers: A comprehensive outlook

Biopolymers are substances naturally produced by living organisms and are hence considered to be eco-friendly and sustainable. Chitosan and cellulose are of specific significance owing to their abundant availability, ease of modification, and application potential. On the environmental front, their coagulating and flocculating effects have helped in wastewater clarification, while minimizing the dependability on synthetic polyelectrolytes. Biopolymer based hydrogels and nanocomposite films have functioned as effective biosorbents in removing an array of organic and inorganic pollutants, including xenobiotics, from wastewater. Specifically, they have been vastly harnessed for heavy metal and dye adsorption. They have also played a pivotal part in other environmental applications including anti-desertification, natural bio-sealants for preventing concrete leaks and proton conducting membranes in electrochemical devices. Such recent research on the environmental applications of biopolymers has been comprehensively analysed, thus providing a fresh insight into the future prospects of research in this domain.

A high-performance liquid chromatography-electronic circular dichroism online method for assessing the absolute enantiomeric excess and conversion ratio of asymmetric reactions

Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology.