Anaerobic biotechnological approaches for production of liquid energy carriers from biomass

Co-production of bio-ethanol, xylonic acid and slow-release nitrogen fertilizer from low-cost straw pulping solid residue

A novel bio-refinery sequence yielding varieties of co-products was developed using straw pulping solid residue. This process utilizes neutral sulfite pretreatment which under optimal conditions (160 °C and 3% (w/v) sulfite charge) provides 64.3% delignification while retaining 90% of cellulose and 67.3% of xylan. The pretreated solids exhibited excellent enzymatic digestibility, with saccharification yields of 86.9% and 81.1% for cellulose and xylan, respectively. After pretreatment, the process of semi-simultaneous saccharification and fermentation (S-SSF) and bio-catalysis was investigated. The results revealed that decreased ethanol yields were achieved when solid loading increased from 5% to 30%. An acceptable ethanol yield of 76.8% was obtained at 20% solid loading. After fermentation, bio-catalysis of xylose remaining in fermentation broth resulted in near 100% xylonic acid (XA) yield at varied solid loadings. To complete the co-product portfolio, oxidation ammoniation of the dissolved lignin successfully transformed it into biodegradable slow-release nitrogen fertilizer with excellent agricultural properties.

Luminescence materials for pH and oxygen sensing in microbial cells - structures, optical properties, and biological applications

Luminescence including fluorescence and phosphorescence sensors have been demonstrated to be important for studying cell metabolism, and diagnosing diseases and cancer. Various design principles have been employed for the development of sensors in different formats, such as organic molecules, polymers, polymeric hydrogels, and nanoparticles. The integration of the sensing with fluorescence imaging provides valuable tools for biomedical research and applications at not only bulk-cell level but also at single-cell level. In this article, we critically reviewed recent progresses on pH, oxygen, and dual pH and oxygen sensors specifically for their application in microbial cells. In addition, we focused not only on sensor materials with different chemical structures, but also on design and applications of sensors for better understanding cellular metabolism of microbial cells. Finally, we also provided an outlook for future materials design and key challenges in reaching broad applications in microbial cells.

Glutamate and histidine improve both solvent yields and the acid tolerance response of Clostridium beijerinckii NCP 260

AIMS

This study aims to examine the effect of amino acid supplementation on solvent production by Clostridium beijerinckii during the acetone-butanol fermentation and to determine whether amino acids are involved in the acid tolerance response (ATR), which results in increased solvents.

METHODS AND RESULTS

Fermentation studies with Cl. beijerinckii NCP 260 in limited-nitrogen media supplemented with glutamate, glutamine, lysine, proline, histidine or asparagine revealed that only glutamate, glutamine or histidine increased butanol titres comparable to control media. Acid survival tests at pH 5 showed that glutamate and histidine were effective in protecting Cl. beijerinckii cells against acid shock, and may be involved in the ATR. Using quantitative PCR, the transcription of the glutamine synthetase, nitrogen regulator and glutamate synthase operon (glnA-nitR-gltAB) was monitored during acid shock conditions, and expression of both the nitR and gltA genes was shown to be increased twofold.

CONCLUSIONS

Glutamate and histidine specifically enhance the ATR in Cl. beijerinckii NCP 260, and the genes encoding glutamate synthase and the NitR regulator are both upregulated, predicted to lead to increased endogenous glutamate pools during acidogenesis. This may enhance the ATR and allow more viable cells to enter solventogenesis, thereby increasing butanol titres. Glutamine, glutamate and histidine may also afford protection from butanol stress directly.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using substrates naturally rich in glutamine, glutamate and histidine in industrial fermentations is a promising means to increase acid survival and solvent yields in solventogenic Clostridium.

Selection of yeast strains for bioethanol production from UK seaweeds

Macroalgae (seaweeds) are a promising feedstock for the production of third generation bioethanol, since they have high carbohydrate contents, contain little or no lignin and are available in abundance. However, seaweeds typically contain a more diverse array of monomeric sugars than are commonly present in feedstocks derived from lignocellulosic material which are currently used for bioethanol production. Hence, identification of a suitable fermentative microorganism that can utilise the principal sugars released from the hydrolysis of macroalgae remains a major objective. The present study used a phenotypic microarray technique to screen 24 different yeast strains for their ability to metabolise individual monosaccharides commonly found in seaweeds, as well as hydrolysates following an acid pre-treatment of five native UK seaweed species (Laminaria digitata, Fucus serratus, Chondrus crispus, Palmaria palmata and Ulva lactuca). Five strains of yeast (three Saccharomyces spp, one Pichia sp and one Candida sp) were selected and subsequently evaluated for bioethanol production during fermentation of the hydrolysates. Four out of the five selected strains converted these monomeric sugars into bioethanol, with the highest ethanol yield (13 g L^-1) resulting from a fermentation using C. crispus hydrolysate with Saccharomyces cerevisiae YPS128. This study demonstrated the novel application of a phenotypic microarray technique to screen for yeast capable of metabolising sugars present in seaweed hydrolysates; however, metabolic activity did not always imply fermentative production of ethanol.

The photophysics of LOV-based fluorescent proteins – new tools for cell biology

In this study photophysical characteristics of LOV-based fluorescent proteins which are essential for analytic methods as well as imaging approaches have been comparatively analyzed in detail.

Evaluation of recycling the effluent of hydrogen fermentation for biobutanol production: kinetic study with butyrate and sucrose concentrations

Butyrate in the effluent of hydrogen-producing bioreactor is a potential feed for biobutanol production. For recycling butyrate, this study investigated the kinetics of biobutanol production by Clostridium beijerinckii NRRL B592 from different paired concentrations of butyrate and sucrose in a series of batch reactors. Results show that the lag time of butanol production increased with higher concentration of either sucrose or butyrate. In regression analyses, the maximum specific butanol production potential of 6.49 g g(-1) of dry cell was projected for 31.9 g L(-1) sucrose and 1.3 g L(-1) butyrate, and the maximum specific butanol production rate of 0.87 g d(-1) g(-1) of dry cell was predicted for 25.0 g L(-1) sucrose and 2.6 g L(-1) butyrate. The specific butanol production potential will decrease if more butyrate is added to the reactor. However, both sucrose and butyrate concentrations are weighted equally on the specific butanol production rate. This observation also is true on butanol yield. The maximum butanol yield of 0.49 mol mol(-1) was projected for 25.0 g L(-1) sucrose and 2.3 g L(-1) butyrate. In addition, a confirmation study found butanol yield increased from 0.2 to 0.3 mol mol(-1) when butyrate addition increased from 0 to 1 g L(-1) under low sugar concentration (3.8 g L(-1) sucrose). The existence of butyrate increases the activity of biobutanol production and reduces the fermentable sugar concentration needed for acetone-butanol-ethanol fermentation.

The two stage immobilized column reactor with an integrated solvent recovery module for enhanced ABE production

The production of acetone, butanol, and ethanol (ABE) by fermentation is a process that had been used by industries for decades. Two stage immobilized column reactor system integrated with liquid-liquid extraction was used with immobilized Clostridium acetobutylicum DSM 792, to enhance the ABE productivity and yield. The sugar mixture (glucose, mannose, galactose, arabinose, and xylose) representative to the lignocellulose hydrolysates was used as a substrate for continuous ABE production. Maximum total ABE solvent concentration of 20.30 g L(-1) was achieved at a dilution rate (D) of 0.2h(-1), with the sugar mixture as a substrate. The maximum solvent productivity (10.85 g L(-1)h(-1)) and the solvent yield (0.38 g g(-1)) were obtained at a dilution rate of 1.0 h(-1). The maximum sugar mixture utilization rate was achieved with the present set up which is difficult to reach in a single stage chemostat. The system was operated for 48 days without any technical problems.

Real-time determination of intracellular oxygen in bacteria using a genetically encoded FRET-based biosensor

Background

Molecular oxygen (O₂) is one of the key metabolites of all obligate and facultative aerobic pro- and eukaryotes. It plays a fundamental role in energy homeostasis whereas oxygen deprivation, in turn, broadly affects various physiological and pathophysiological processes. Therefore, real-time monitoring of cellular oxygen levels is basically a prerequisite for the analysis of hypoxia-induced processes in living cells and tissues.

Results

We developed a genetically encoded Förster resonance energy transfer (FRET)-based biosensor allowing the observation of changing molecular oxygen concentrations inside living cells. This biosensor named FluBO (fluorescent protein-based biosensor for oxygen) consists of the yellow fluorescent protein (YFP) that is sensitive towards oxygen depletion and the hypoxia-tolerant flavin-binding fluorescent protein (FbFP). Since O₂ is essential for the formation of the YFP chromophore, efficient FRET from the FbFP donor domain to the YFP acceptor domain only occurs in the presence but not in the absence of oxygen. The oxygen biosensor was used for continuous real-time monitoring of temporal changes of O₂ levels in the cytoplasm of Escherichia coli cells during batch cultivation.

Conclusions

FluBO represents a unique FRET-based oxygen biosensor which allows the non-invasive ratiometric readout of cellular oxygen. Thus, FluBO can serve as a novel and powerful probe for investigating the occurrence of hypoxia and its effects on a variety of (patho)physiological processes in living cells.

Characterization of a zinc-containing alcohol dehydrogenase with stereoselectivity from the hyperthermophilic archaeon Thermococcus guaymasensis

An alcohol dehydrogenase (ADH) from hyperthermophilic archaeon Thermococcus guaymasensis was purified to homogeneity and was found to be a homotetramer with a subunit size of 40 ± 1 kDa. The gene encoding the enzyme was cloned and sequenced; this gene had 1,095 bp, corresponding to 365 amino acids, and showed high sequence homology to zinc-containing ADHs and l-threonine dehydrogenases with binding motifs of catalytic zinc and NADP(+). Metal analyses revealed that this NADP(+)-dependent enzyme contained 0.9 ± 0.03 g-atoms of zinc per subunit. It was a primary-secondary ADH and exhibited a substrate preference for secondary alcohols and corresponding ketones. Particularly, the enzyme with unusual stereoselectivity catalyzed an anti-Prelog reduction of racemic (R/S)-acetoin to (2R,3R)-2,3-butanediol and meso-2,3-butanediol. The optimal pH values for the oxidation and formation of alcohols were 10.5 and 7.5, respectively. Besides being hyperthermostable, the enzyme activity increased as the temperature was elevated up to 95°C. The enzyme was active in the presence of methanol up to 40% (vol/vol) in the assay mixture. The reduction of ketones underwent high efficiency by coupling with excess isopropanol to regenerate NADPH. The kinetic parameters of the enzyme showed that the apparent K(m) values and catalytic efficiency for NADPH were 40 times lower and 5 times higher than those for NADP(+), respectively. The physiological roles of the enzyme were proposed to be in the formation of alcohols such as ethanol or acetoin concomitant to the NADPH oxidation.

Optimization of H2SO4-catalyzed hydrothermal pretreatment of rapeseed straw for bioconversion to ethanol: focusing on pretreatment at high solids content

A central composite design of response surface method was used to optimize H(2)SO(4)-catalyzed hydrothermal pretreatment of rapeseed straw, in respect to acid concentration (0.5-2%), treatment time (5-20 min) and solid content (10-20%) at 180 degrees C. Enzymatic hydrolysis and fermentation were also measured to evaluate the optimal pretreatment conditions for maximizing ethanol production. The results showed that acid concentration and treatment time were more significant than solid content for optimization of xylose release and cellulose recovery. Pretreatment with 1% sulfuric acid and 20% solid content for 10 min at 180 degrees C was found to be the most optimal condition for pretreatment of rapeseed straw for ethanol production. After pretreatment at the optimal condition and enzymatic hydrolysis, 75.12% total xylan and 63.17% total glucan were converted to xylose and glucose, respectively. Finally, 66.79% of theoretical ethanol yielded after fermentation.

ATP in current biotechnology: regulation, applications and perspectives

Adenosine tri-phosphate (ATP), the most important energy source for metabolic reactions and pathways, plays a vital role in the growth of industrial strain and the production of target metabolites. In this review, current advances in manipulating ATP in industrial strains, including altering NADH availability, and regulating NADH oxidation pathway, oxygen supply, proton gradient, the electron transfer chain activity and the F(0)F(1)-ATPase activity, are summarized and discussed. By applying these strategies, optimal product concentrations, yields and productivity in industrial biotechnology have been achieved. Furthermore, the mechanisms by which ATP extends the substrate utilization spectra and enhances the ability to challenge harsh environmental stress have been elucidated. Finally, three critical issues related to ATP manipulation have been addressed.