Enzymatic Synthesis of Pyruvic Acid and L-Lactic Acid from Carbon Dioxide

Carbon Dioxide as Chemical Feedstock

BackgroundPolylactic acid (PLA), a biodegradable polymer, has the potential to replace (at least partially) traditional petroleum-based plastics, minimizing “white pollution”. However, cost-effective production of optically pure L-lactic acid is needed to achieve the full potential of PLA. Currently, starch-based glucose is used for L-lactic acid fermentation by lactic acid bacteria. Due to its competition with food resources, an alternative non-food substrate such as cellulosic biomass is needed for L-lactic acid fermentation. Nevertheless, the substrate (sugar stream) derived from cellulosic biomass contains significant amounts of xylose, which is unfermentable by most lactic acid bacteria. However, the microorganisms that do ferment xylose usually carry out heterolactic acid fermentation. As a result, an alternative strain should be developed for homofermentative production of optically pure L-lactic acid using cellulosic biomass.ResultsIn this study, an ethanologenic Escherichia coli strain, SZ470 (ΔfrdBC ΔldhA ΔackA ΔpflB ΔpdhR ::pflBp6-acEF-lpd ΔmgsA), was reengineered for homofermentative production of L-lactic acid from xylose (1.2 mole xylose = > 2 mole L-lactic acid), by deleting the alcohol dehydrogenase gene (adhE) and integrating the L-lactate dehydrogenase gene (ldhL) of Pediococcus acidilactici. The resulting strain, WL203, was metabolically evolved further through serial transfers in screw-cap tubes containing xylose, resulting in the strain WL204 with improved anaerobic cell growth. When tested in 70 g L-1 xylose fermentation (complex medium), WL204 produced 62 g L-1 L-lactic acid, with a maximum production rate of 1.631 g L-1 h-1 and a yield of 97% based on xylose metabolized. HPLC analysis using a chiral column showed that an L-lactic acid optical purity of 99.5% was achieved by WL204.ConclusionsThese results demonstrated that WL204 has the potential for homofermentative production of L-lactic acid using cellulosic biomass derived substrates, which contain a significant amount of xylose.

This special issue contains peer-reviewed manuscripts presented at the 10th International Conference on CO2 Utilization (ICCDU-X), Tianijn, China, May 17-21, 2009. The guest editor is grateful to Tianjin University, National Natural Science Foundation of China, Tianjin Key Laboratory of Catalysis Science & Technology, Agilent, Quantachrome, Frontier of Chemical Engineering in China and Energy & Environmental Science for their sponsorship. Carbon dioxide is the largest man-made greenhouse gas. The emission of carbon dioxide has led to a more and more serious global warming. How to deal with carbon dioxide is a significant challenge to governments, industries and societies worldwide. On the other hand, it has been well known that carbon dioxide is the largest carbon resource for various syntheses. The utilization or chemical fixation of carbon dioxide would be a final solution to the global carbon dioxide problem. This special issue focuses on the utilization of carbon dioxide with other related important aspects, like capture, separation and low-carbon emission options. Especially, several authors presented their new ideas for the first time in papers in this special issue. The guest editor believes that the papers presented here will be helpful for the future development of this truly international field. The guest editor thanks all the authors for their excellent contributions and also for their understanding and collaborations. The guest editor also acknowledges all the referees for their reviews that make this quality issue possible.

A circular, sustainable bioeconomy is gaining ground across the globe. Green synthesis, which uses renewable feedstock, is becoming a mainstay of the chemical industry. To produce polylactic acid, a biodegradable plastic, researchers are increasingly focusing on low-cost substrates to produce lactic acid. In the United Arab Emirates, one such low-cost substrate with readily available reducing sugar is the date fruit pomace (DFP). It is a solid residue obtained from date fruit processing and contains 35% sugars on a dry basis. It is a potential feedstock for lactic acid fermentation. Here, the effects of media supplements and fermentation parameters on L-lactic acid production by Lactobacillus casei were investigated. The lactic acid yield improved when the pH was maintained at 6.2 during incubation and the enzyme Cellic CTec2 was used to release sugar from the pomace. At a controlled pH, a lactic acid concentration of 292 ± 1.2 g/kg DFP was achieved when 80 g DFP was inoculated with bacteria (3.9 × 1010 colony-forming units) and incubated for 7 days. Upon hydrolysis with 40 FPU/g DFP Cellic CTec2, the sugar content increased to 482 g/kg DFP, and the lactic acid concentration increased to 457 ± 1.4 g/kg DFP. Using n-butanol, via phase partitioning, 78.9% pure L-lactic acid was extracted from the fermentation broth.

Spent sulfite liquor (SSL), a waste stream from wood pulp production, has great potential as carbon source for future industrial fermentations. In the present study, SSL was separated into a hemicellulose derived sugar syrup (HDSS) and a lignosulfonic fraction by simulated moving bed chromatography. The recovery of SSL sugars in the HDSS was 89% and the fermentation inhibitors furfural, 5-hydroxymethylfurfural and acetic acid were removed by 98.7%, 60.5% and 75.5%, respectively. The obtained sugars have been converted to L-lactic acid, a building block for bioplastics, by fermentation with the lactic acid bacterium Enterococcus mundtii DSM4838. Batch fermentations on HDSS produced up to 56.3 g/L L-lactic acid. Simultaneous conversion of pentose and hexose sugars during fed-batch fermentation of wildtype E. mundtii led to 87.9 g/L optically pure (>99%) L-lactic acid, with maximum productivities of 3.25 g/L.h and yields approaching 1.00 g/g during feeding phase from HDSS as carbon source.

For production of mannitol in combination with pure L-lactic acid or pyruvate, the D- and L-lactate dehydrogenase genes (ldhD and ldhL) of a mannitol-producing Lactobacillus fermentum strain were cloned and stepwise inactivated. For inactivation of both ldh genes by a gene replacement technique, deletion constructs removing a 0.4-kb fragment from the promoter and the 5' end region of the ldh genes were used. The first inactivation mutant, designated L. fermentum GRL1030, carried the deletion in ldhD (DeltaldhD). A double mutant, DeltaldhD-DeltaldhL, was constructed by the inactivation of the ldhL gene of strain GRL1030, resulting in strain L. fermentum GRL1032. The correctness of the both mutants was confirmed at the DNA level by polymerase chain reaction, as shown by the absence of ldh transcripts by northern blotting and as a lack of the corresponding enzyme activity. In bioreactor cultivations, the single mutant GRL1030 produced mannitol and L-lactic acid as expected. Mannitol and lactic acid yields and productivities were practically unaffected by deletion of the ldhD gene. The double mutant GRL1032 produced mannitol and pyruvate as expected. However, although the yield of mannitol from fructose remained high, its volumetric productivity was reduced. The double mutation negatively affected the glucose consumption rate, resulting in reduced cellular growth. In addition to pyruvate, the double mutant produced 2,3-butanediol. More surprisingly, some lactic acid was still produced.

Background and objective Lactic acid bacteria (LAB) are generous producers of many industrially important products. Of these products, optically pure lactic acid is of great value as it is essential for production of highly crystalline poly-lactic acid, which is the most widely used biodegradable synthetic polymer. Hence, this study aimed to screen for thermotolerant LAB from a new source, which is fresh water samples collected from the coast of the Nile River, Egypt, and then evaluate their ability to produce optically pure L-lactic acid. Materials and methods LAB strains were isolated at 50°C and evaluated for producing optically pure L-lactic acid using high-performance liquid chromatography and BF-5. Effects of medium containing different sugar sources, incubation temperature, and initial pH of the medium on the purity and productivity of L-lactic acid were also studied. Results and discussion All obtained isolates were capable of producing optically pure L-lactic acid on different sugar sources. Changing the incubation temperature to 30°C positively affected both productivity and optical purity, which reached 5.0 g/l of 100% optically pure L-lactic acid. On the contrary, pH of the medium was confirmed to be also one of the major factors affecting productivity and optical purity of obtained L-lactic acid. For our isolates, pH 7.0 was the optimum one for the production process. The four promising producers of 100% optically pure L-lactic acid were molecularly identified as Lactiplantibacillus sp. Conclusion This is the first study describing the evaluation of the ability of fresh water LAB isolated from the Nile River to produce optically pure L-lactic acid.

High-pressure phase equilibrium data for the l-lactic acid + (propane + ethanol) and the l-lactic acid + (carbon dioxide + ethanol) systems

Cocrystallization as a tool to solve deliquescence issues: The case of l-lactic acid

Background. One of the key approaches to reducing the long-term effects of global warming consists in capturing, transporting and disposing and/or burial of carbon dioxide. The Russian Federation is one of the leaders in carbon dioxide emissions. At the same time, having great potential in the field of CO2 burial in the subsoil, there are currently no industrial projects for capturing, transporting and utilizing and (or) storing CO2.Aim. To study of the retention mechanisms and burial features of carbon dioxide within various geological formations.Materials and methods. Based on the analysis of extensive material, a review of existing options for the utilization and storage of carbon dioxide in the bowels has been prepared.Results. Burial assumes CO2 injection into rock layers, which are capable of its absorption and safe long-term retention. Various options for the burial of carbon dioxide in the Earth interior are considered. The main ones are layers of depleted hydrocarbon deposits and mineralized aquifers. Also, carbon dioxide storage can be carried out in undeveloped coal seams, saline and basalt formations. The basic mechanisms of retention, necessary geological conditions and characteristics of potential reservoirs are described. The risks and uncertainties of burial in various geological formations are analyzed. Examples of the world’s most significant projects for the utilization and disposal of CO2 in the Earth interior are given. Such as Sleipner in Norway, In-Salah in Algeria, etc. It is indicated that the potential of Russia in the field of utilization and (or) disposal of carbon dioxide in the bowels is quite high, but it has not been fully assessed.Conclusion. At present, the most studied and tested options for the utilization and storage of carbon dioxide in the Earth interior are as follows: the use of carbon dioxide as an agent in the methods of enhanced oil recovery, the storage of CO2 in the strata of depleted deposits of hydrocarbon raw materials and in mineralized aquifers.It is necessary to concentrate efforts on a purposeful geological study of various conditions for storing carbon dioxide in the Russian Earth interior, as well as on the development of uniform requirements for the geological parameters of CO2 underground storage facilities.

In agricultural systems, soil carbon dioxide emissions and physical properties are thought to depend largely on management practices. This field study was carried out in a semi-arid region of eastern Tunisia to evaluate the effects of tillage management on soil carbon dioxide emissions and related physical properties; bulk density (BD), penetration resistance (PR), total porosity (TP) and air-filled porosity (AFP). Tillage management treatments included plowing with a moldboard plow or a disk plow to different depths, described here as shallow (10 cm), medium (15 cm) and deep (25 cm). No-tillage was also considered as a control plot. Correlation analysis was used to explore how soil carbon dioxide emissions (CO2) were related to the other studied properties. The results showed higher carbon dioxide (CO2) emissions (p < .05) from tilled soil compared to no-till (NT), regardless of the tillage management. No significant differences in carbon dioxide (CO2) emissions were found between moldboard and disk plow tillage at the same tillage depth. Soil carbon dioxide release was the highest after deep tillage (moldboard = 0.101 t ha−1 and disk plow = 0.107 t ha−1) suggesting that deeper tillage to 25 cm promoted higher carbon dioxide (CO2) emissions. Significant differences with tillage were observed in bulk density (BD) and penetration resistance (PR) compared to no-tillage. Correlations of carbon dioxide emissions to soil physical properties across all the tillage treatments indicated significant negative relationships between carbon dioxide (CO2) emissions and soil bulk density (BD) and penetration resistance (PR) and significant positive relationships between carbon dioxide (CO2) and total porosity (TP) and air-filled porosity (WFP) suggesting that these soil attributes are important controlling factors of carbon dioxide (CO2) emissions.

BackgroundThe demand for lactic acid has been increasing considerably because of its use as a monomer for the synthesis of polylactic acid (PLA), which is a promising and environment-friendly alternative to plastics derived from petrochemicals. Optically pure l-lactic acid is essential for polymerization of PLA. The high fermentation cost of l-lactic acid is another limitation for PLA polymers to compete with conventional plastics.Methodology/Principal FindingsA Bacillus sp. strain 2–6 for production of l-lactic acid was isolated at 55°C from soil samples. Its thermophilic characteristic made it a good lactic acid producer because optically pure l-lactic acid could be produced by this strain under open condition without sterilization. In 5-liter batch fermentation of Bacillus sp. 2–6, 118.0 g/liter of l-lactic acid with an optical purity of 99.4% was obtained from 121.3 g/liter of glucose. The yield was 97.3% and the average productivity was 4.37 g/liter/h. The maximum l-lactic acid concentration of 182.0 g/liter was obtained from 30-liter fed-batch fermentation with an average productivity of 3.03 g/liter/h and product optical purity of 99.4%.Conclusions/SignificanceWith the newly isolated Bacillus sp. strain 2–6, high concentration of optically pure l-lactic acid could be produced efficiently in open fermentation without sterilization, which would lead to a new cost-effective method for polymer-grade l-lactic acid production from renewable resources.

ConspectusGlobal climate change caused by the excessive emission of greenhouse gases has become one of the greatest threats to human survival in the 21st century. Carbon dioxide is the main greenhouse gas on earth and has brought about serious environmental problems nowadays. On the basis of the current situation, it is urgent to reach the peak of carbon dioxide emission and then achieve carbon neutrality via policy support and engineering strategies within advanced materials and technologies. Carbon neutrality requires an appropriate balance between the emission and reduction of carbon dioxide. The emission of carbon dioxide mainly comes from modern industries, and the reduction requires several steps, including capture, conversion, and application. On one hand, it can reduce carbon dioxide emission by promoting the transformation of industrial structure. On the other hand, it is necessary to remove high-level carbon dioxide existing in the atmosphere by physical and chemical methods such as adsorption capture and catalytic conversion.This Account showcases our recent progress on carbon neutrality for the reduction of carbon dioxide through capture and conversion methods within advanced materials and technologies. We mainly focus on the right side of the carbon scale and have made some advances such as moisture-swing chemisorption for carbon dioxide capture, the reduction of oxygen-containing carbon dioxide, and the photothermal catalytic conversion of carbon dioxide. Different from previous studies, our work is about developing materials and techniques for practical applications. First, we have made attempts to develop cheap sorbents with high stability and a high adsorption capacity. Second, we have reported a moisture-swing technique with the capability of directly capturing carbon dioxide from the atmosphere by relying on the humidity variation with low energy consumption. This technique is promising for realizing real-time carbon dioxide capture and utilization, which avoids high-cost storage and transport processes. Third, our work on carbon dioxide utilization focuses on efficient conversion under practical conditions. For instance, we have developed perovskite catalysts for converting carbon dioxide to carbon monoxide in an oxygen-containing environment. Furthermore, core–shell catalysts have been reported for carbon dioxide conversion with a high selectivity of 83% driven by solar energy. In addition, practical applications of captured carbon dioxide have been explored with respect to carbon dioxide-assisted graphene exfoliation, keeping fruit fresh, and crop growth promotion with carbon dioxide gas fertilizer. A future perspective on the challenges and opportunities for carbon neutrality has been provided on the basis of our experimental studies and theoretical predictions. It is expected that this Account will promote tremendous effort in the development of advanced materials and engineering technologies toward the realization of carbon neutrality by the middle of this century.

Efficient production of l-lactic acid with high optical purity by alkaliphilic Bacillus sp. WL-S20

Population growth and trends are centrally important to the environment because it helps to determine the environmental impact of human activities. In this study, the World Bank database has been used. Here, carbon dioxide (CO2) emissions, and energy intensity (EI) are considered as environmental indicators. The population indicators are the proportion of the population aged 15-64 years, and the percentage of the urban population. The Gross Domestic Product (GDP) is considered a development indicator in a country. This study tries to identify the association between population environment and development. Correlation analysis has been employed to know association and Path analysis is used to determine the important factors for environmental impacts such as carbon dioxide (CO2) emissions. The result presents that the zero-order correlation exists among energy intensity (EI), the proportion of the population aged 15-64 (P15-64), urbanization (UR), gross domestic product (GDP) per capita (US$), total population (P) ) and carbon dioxide (CO2) emission in Bangladesh and India. It is observed that 8 paths for Bangladesh and 7 paths for India out of each 12 hypothesized paths are found to be statistically significant. In Bangladesh, the total effects of exogenous variables like as energy intensity (X1) and population aged 15-64 (X2) are observed negative direction on carbon dioxide emissions (X6) and the remaining variable like as urbanization (X3) is observed as positive direction on carbon dioxide emissions. However, in India total effects of these two exogenous variables population aged 15-64 (X2) and urbanization (X3) are observed positive direction on carbon dioxide emissions (X6) and the remaining variable like as energy intensity (X1) is observed negative direction on carbon dioxide emissions (X6). The total effects of endogenous variables like as GDP per capita (X4) show a negative direction on carbon dioxide emissions and population (X5) shows a positive direction on carbon dioxide emissions. The study demonstrates that CO2 emission is important for environmental impact in Bangladesh and India. There is a strong association between population, GDP per capita, energy consumption and urbanization and CO2 emission in Bangladesh and India. The factors of CO2 emissions play an important role in environmental degradation. Thus, attention should be focused on using low energy consumption, and proper urbanization, particularly on modern technology which assures fewer uses of CO2 emissions in Bangladesh and India.