Impact of impurities in biodiesel-derived crude glycerol on the fermentation by Clostridium pasteurianum ATCC 6013

A systematic review on utilization of biodiesel-derived crude glycerol in sustainable polymers preparation

With the rapid development of biodiesel, biodiesel-derived glycerol has become a promising renewable bioresource. The key to utilizing this bioresource lies in the value-added conversion of crude glycerol. While purifying crude glycerol into a pure form allows for diverse applications, the intricate nature of this process renders it costly and environmentally stressful. Consequently, technology facilitating the direct utilization of unpurified crude glycerol holds significant importance. It has been reported that crude glycerol can be bio-transformed or chemically converted into high-value polymers. These technologies provide cost-effective alternatives for polymer production while contributing to a more sustainable biodiesel industry. This review article describes the global production and quality characteristics of biodiesel-derived glycerol and investigates the influencing factors and treatment of the composition of crude glycerol including water, methanol, soap, matter organic non-glycerol, and ash. Additionally, this review also focused on the advantages and challenges of various technologies for converting crude glycerol into polymers, considering factors such as the compatibility of crude glycerol and the control of unfavorable factors. Lastly, the application prospect and value of crude glycerol conversion were discussed from the aspects of economy and environmental protection. The development of new technologies for the increased use of crude glycerol as a renewable feedstock for polymer production will be facilitated by the findings of this review, while promoting mass market applications.

Biochemical and molecular characterization of a novel glycerol dehydratase from Klebsiella pneumoniae 2e with high tolerance against crude glycerol impurities

BACKGROUND

The direct bioconversion of crude glycerol, a byproduct of biodiesel production, into 1,3-propanediol by microbial fermentation constitutes a remarkably promising value-added applications. However, the low activity of glycerol dehydratase, which is the key and rate-limiting enzyme in the 1,3-propanediol synthetic pathway, caused by crude glycerol impurities is one of the main factors affecting the 1,3-propanediol yield. Hence, the exploration of glycerol dehydratase resources suitable for crude glycerol bioconversion is required for the development of 1,3-propanediol-producing engineered strains.

RESULTS

In this study, the novel glycerol dehydratase 2eGDHt, which has a tolerance against crude glycerol impurities from Klebsiella pneumoniae 2e, was characterized. The 2eGDHt exhibited the highest activity toward glycerol, with Km and Vm values of 3.42 mM and 58.15 nkat mg-1, respectively. The optimum pH and temperature for 2eGDHt were 7.0 and 37 °C, respectively. 2eGDHt displayed broader pH stability than other reported glycerol dehydratases. Its enzymatic activity was increased by Fe2+ and Tween-20, with 294% and 290% relative activities, respectively. The presence of various concentrations of the crude glycerol impurities, including NaCl, methanol, oleic acid, and linoleic acid, showed limited impact on the 2eGDHt activity. In addition, the enzyme activity was almost unaffected by the presence of an impurity mixture that mimicked the crude glycerol environment. Structural analyses revealed that 2eGDHt possesses more coil structures than reported glycerol dehydratases. Moreover, molecular dynamics simulations and site-directed mutagenesis analyses implied that the existence of unique Val744 from one of the increased coil regions played a key role in the tolerance characteristic by increasing the protein flexibility.

CONCLUSIONS

This study provides insight into the mechanism for enzymatic action and the tolerance against crude glycerol impurities, of a novel glycerol dehydratase 2eGDHt, which is a promising glycerol dehydratase candidate for biotechnological conversion of crude glycerol into 1,3-PDO.

Fermentation of biodiesel-derived crude glycerol to 1,3-propanediol with bio-wastes as support matrices: Polynomial prediction model

Biodiesel production from used cooking oil is sustainable alternative, for bio-energy production. The process generates residual crude glycerol (RCG) as the major energy-rich waste which can be used to produce various bio-based chemicals like 1,3-propanediol (1,3-PDO) through biotechnological interventions. This RCG contains several impurities like methanol, soap, organic materials, salts non-transesterified fatty acids and metals in varied concentrations. These impurities significantly affect yield and productivity of the bio-process due to their marked microbial toxicity. In this work, previously isolated Clostridium butyricum L4 was immobilized on various abundantly available cheap bio-wastes (like rice straw, activated carbon and corn cob) to explore advantages offered and improve tolerance to various feed impurities. Amongst these, shredded rice straw was found most suitable candidate for immobilization and results in maximum improvement in 1,3-PDO production (18.4%) with highest porosity (89.28%), lowest bulk density (194.48Kg/m3), and highest cellular biofilm density (CFU/g-8.4 ×1010) amongst the three matrices. For practical purposes, recyclability was evaluated and it was concluded that even after reusing for five successive cycles the production retained to ∼82.4%. Subsequently, polynomial model was developed using 30 runs central composite factorial design experiments having coefficient of regression (R²) as 0.9520, in order to predict yields under different immobilization conditions for 1,3-PDO production. Plackett-Burman was employed (Accuracy= 99.17%) to screen significant toxic impurities. Based on statistical analysis six impurities were found to be significantly influential on PDO production in adverse manner. With negative coefficient of estimate (COE) varying in decreasing order: Linoleic acid >Oleic acid >Stearic acid >NaCl>K2SO4 >KCl. The study illustrates practical application for repurposing waste glycerol generated from biodiesel plants, thus developing improved agnostic process along with yield production models.

Strain evolution and novel downstream processing with integrated catalysis enable highly efficient co-production of 1,3-Propanediol and organic acid esters from crude glycerol

Bioconversion of natural microorganisms generally results in a mixture of various compounds. Downstream processing (DSP) which only targets a single product often lacks economic competitiveness due to incomplete use of raw material and high cost of waste treatment for by-products. Here, we show with the efficient microbial conversion of crude glycerol by an artificially evolved strain and how a catalytic conversion strategy can improve the total products yield and process economy of the DSP. Specifically, Clostridium pasteurianum was first adapted to increased concentration of crude glycerol in a novel automatic laboratory evolution system. At m³ scale bioreactor the strain achieved a simultaneous production of 1,3-propanediol (PDO), acetic and butyric acids at 81.21, 18.72 and 11.09 g/L within only 19 h, respectively, representing the most efficient fermentation of crude glycerol to targeted products. A heterogeneous catalytic step was developed and integrated into the DSP process to obtain high-value methyl esters from acetic and butyric acids at high yields. The co-production of the esters also greatly simplified the recovery of PDO. For example, a cosmetic grade PDO (96% PDO) was easily obtained by a simple single-stage distillation process (with an overall yield more than 77%). This integrated approach provides an industrially attractive route for the simultaneous production of three appealing products from the crude glycerol fermentation broth, which greatly improve the process economy and ecology. This article is protected by copyright. All rights reserved.

Glycerol as a substrate for actinobacteria of biotechnological interest: Advantages and perspectives in circular economy systems

Actinobacteria represent a ubiquitous group of microorganisms widely distributed in ecosystems. They have diverse physiological and metabolic properties, including the production of extracellular enzymes and a variety of secondary bioactive metabolites, such as antibiotics, immunosuppressants, and other compounds of industrial interest. Therefore, actinobacteria have been used for biotechnological purposes for more than three decades. The development of a biotechnological process requires the evaluation of its cost/benefit ratio, including the search for economic and efficient substrates for microorganisms development. Biodiesel is a clean, renewable, quality and economically viable source of energy, which also contributes to the conservation of the environment. Crude glycerol is the main by-product of biodiesel production and has many properties, so it has a commercial value that can be used to finance the biofuel production process. Actinobacteria can use glycerol as a source of carbon and energy, either pure o crude. A circular economy system aims to eliminate waste and pollution, keep products and materials in use, and regenerate natural systems. Although these principles are not yet met, some approaches are being made in this direction; the transformation of crude glycerol by actinobacteria is a process with great potential to be scaled on an industrial level. This review discusses the reports on glycerol as a promising source of carbon and energy for obtaining biomass and high-added value products by actinobacteria. Also, the factors influencing the biomass and secondary metabolites production in bioreactors are analyzed, and the tools available to overcome those that generate the main problems are discussed.

Two-Stage Anaerobic Codigestion of Crude Glycerol and Micro-Algal Biomass for Biohydrogen and Methane Production by Anaerobic Sludge Consortium

Optimization of factors affecting biohydrogen production from the codigestion of crude glycerol and microalgal biomass by anaerobic sludge consortium was conducted. The experiments were designed by a response surface methodology with central composite design. The factors affecting the production of hydrogen were the concentrations of crude glycerol, microalgal biomass, and inoculum. The maximum hydrogen production (655.1 mL-H2/L) was achieved with 13.83 g/L crude glycerol, 23.1 g-VS/L microalgal biomass, and 10.3% (v/v) inoculum. The hydrogenic effluents obtained under low, high, and optimal conditions were further used as substrates for methane production. Methane production rates and methane yield of 868.7 mL-CH4/L and 2.95 mL-CH4/L-h were attained with the effluent produced under optimum conditions. The use of crude glycerol and microalgal biomass as cosubstrates had an antagonistic effect on biohydrogen production and a synergistic effect on methane fermentation. The two-stage process provided a more attractive solution, with a total energy of 1.27 kJ/g-VSadded, than the one-stage process.

Optimization of a Recombinant Lectin Production in Pichia pastoris Using Crude Glycerol in a Fed-Batch System

The production of heterologous proteins for medical use is an important area of interest. The optimization of the bioprocesses includes the improvement of time, costs, and unit operations. Our study shows that a lectin fraction from Tepary bean (Phaseolus acutifolius) (TBLF) has cytotoxic effects on colon cancer cells and in vivo antitumorigenic activity. However, the low-yield, time-consuming, and expensive process made us focus on the development of a strategy to obtain a recombinant lectin using engineered Pichia pastoris yeast. Pure glycerol is one of the most expensive supplies; therefore, we worked on process optimization using crude glycerol from biodiesel production. Recombinant lectin (rTBL-1) production and purification were evaluated for the first time by an experimental design where crude glycerol (G65) was used and compared against pure glycerol (G99) in a controlled stirred-tank bioreactor with a fed-batch system. The recombinant lectin was detected and identified by SDS-PAGE, Western blot, and UHPLC–ESI–QTOF/MS analysis. The results show that the recombinant lectin can be produced from G65 with no significant differences with respect to G99: the reaction rates were 2.04 and 1.43 mg L−1 h−1, and the yields were 264.95 and 274.67 mgL−1, respectively. The current low cost of crude glycerol and our results show the possibility of producing heterologous proteins using this substrate with high productivity.

Production of 1,3-propanediol by Lactobacillus diolivorans from agro-industrial residues and cactus cladode acid hydrolyzate

This study evaluated the bioproduction of 1,3-propanediol by Lactobacillus diolivorans in the medium based on agro-industrial residues and vegetal biomass substituting the MRS medium components. It was performed on a set of acid treatments and batch fermentations assays with crude glycerol (TCG) from biodiesel production, corn steep liquor (CSL), and cactus cladode hydrolyzate (CCH). Firstly, it was carried out on batch fermentation with different pure glycerol concentrations in MRS medium which was carried out, and the best condition achieved 4.66 g/L and 0.61 g/g of 1,3-PDO production and yield, respectively. Then, the TCG was evaluated, and a discrete increase of 1,3-PDO was observed. The replacement of the MRS medium nutrients by CLS was assessed, at different concentrations, for bacteria growth, and 5% of CLS reproduced the same biomass formation compared to the bacteria growth in MRS medium. It was also added cactus cladode hydrolyzate as the only sugar source, which showed a 1,3-PDO production close to the medium with pure glucose. Finally, a B-complex vitamin was added to the batch fermentation medium composed of TCG, CLS, and CCH, replacing all the costly MRS components. In this medium, the production of 1,3-propanediol was 6.57 g/L with a yield of 0.75 g/g. It means an increment of 29% and 19%, respectively, compared to MRS medium. Therefore, the combination of treated crude glycerol, corn steep liquor, and cactus cladode hydrolyzate has excellent potential for 1,3-PDO production by L. diolivorans.

Crude glycerol impurities improve Rhizomucor miehei lipase production by Pichia pastoris

Crude glycerol, a by-product of biodiesel production, was employed as the carbon source to produce lipase using Pichia pastoris. Under identical fermentation conditions, cell growth and lipase activity were improved using crude glycerol instead of pure glycerol. The impacts of crude glycerol impurities (methyl ester, grease, glycerol, methanol, and metal ions Na⁺, Ca²⁺, and Fe³⁺) on lipase production were investigated. Impurities accelerated P. pastoris entering the stationary phase. Na⁺, Ca²⁺, and grease in waste crude glycerol were the main factors influencing higher lipase activity. Through response surface optimization of Ca²⁺, Na⁺, and grease concentrations, lipase activity reached 1437 U/mL (15,977 U/mg), which was 2.5 times that of the control. This study highlights the economical and highly efficient valorization of crude glycerol, demonstrating its possible utilization as a carbon source to produce lipase by P. pastoris without pretreatment.

Physiological Characterization of a Novel Wild-Type Yarrowia lipolytica Strain Grown on Glycerol: Effects of Cultivation Conditions and Mode on Polyols and Citric Acid Production

A new yeast wild-type Yarrowia lipolytica isolate presented efficient growth on glycerol. During flask cultures, nitrogen limitation led to the secretion of sugar-alcohols as the major metabolites of the process (mannitol, arabitol and erythritol), whereas insignificant quantities of citrate were synthesized. Although in some instances high initial glycerol concentrations were employed (≈150 g/L), remarkable glycerol assimilation and polyol secretion was observed. Total polyols ≈ 52 g/L (conversion yield on glycerol consumed = 0.43 g/g) was recorded in the flask experiments. The sugar-alcohol production bioprocess was successfully simulated with the aid of a modified Velhlust–Aggelis model that fitted very well with the experimental data, while optimized parameter values seemed to be quite consistent. In bioreactor trials, a noticeable metabolic shift towards citric acid production was observed, while simultaneously insignificant polyol quantities were produced. In fed-batch bioreactor experiments, a total citric acid quantity ≈ 102 g/L was recorded—one of the highest in the literature for wild-type Y. lipolytica strains. This metabolic transition was due to higher oxygen saturation into the medium that occurred in the bioreactor experiments compared with the flasks. Cellular lipids produced in the bioreactor trial contained higher concentrations of unsaturated fatty acids compared with those produced in flasks.

Sustainable and stepwise waste-based utilisation strategy for the production of biomass and biofuels by engineered microalgae

Waste streams have emerged as potential feedstocks for biofuel production via microbial bioconversion. Metabolic engineering of the microalga Phaeodactylum tricornutum in its lipid biosynthetic pathways has been conducted with an aim to improve lipid production. However, there has been only limited achievement in satisfying biofuel demands by utilising extracellular organic carbons from low-cost waste streams. Herein, we present a successive staged cultivation mode, based on a previously engineered strain that co-overexpresses two key triacylglycerol biosynthesis genes. We first optimised microalgal biomass and lipid production by using food waste hydrolysate and crude glycerol as the cultivation media. Food waste hydrolysate (5% v/v) is a low-cost organic carbon source for enhanced microalgal biomass production, and the resulting lipid concentration was 1.08-fold higher with food-waste hydrolysate than that of the defined medium. Additionally, the resultant lipid concentration after using crude glycerol (100 mM) was 1.24-fold higher than that using the defined medium. Two carbon feeding modes (hybrid and sequential) were also performed to investigate the potential of engineered P. tricornutum with preliminary mechanistic analyses. The biodiesel properties of lipids produced in the hybrid mode were evaluated for potential application prospects. Collectively, this study demonstrates a waste stream utilisation strategy for efficient and sustainable microalgal biofuel production.

From Organic Wastes to Bioplastics: Feasibility of Nonsterile Poly(3-hydroxybutyrate) Production by Zobellella denitrificans ZD1

Poly(3-hydroxybutyrate) (PHB)—a renewable and biodegradable polymer—is a promising alternative to nonbiodegradable synthetic plastics that are derived from petrochemicals. The methods currently employed for PHB production are costly, in part, due to the expensive cultivation feedstocks and the need to sterilize the culture medium, which is energy-intensive. This study investigates the feasibility of nonsterile PHB production from several saline organic wastes using a salt-tolerant strain, Zobellella denitrificans ZD1 (referred to as strain ZD1). Factors such as the pH, salinity, carbon/nitrogen (C/N) ratio, nitrogen source, and electron acceptor that might affect the growth of strain ZD1 and its PHB production were determined. Our results showed successful nonsterile PHB production by growing the strain ZD1 on nonsterile synthetic crude glycerol, high-strength saline wastewater, and real municipal wastewater-activated sludge under saline conditions. The PHB production was significantly enhanced when the levels of salts and nitrate-nitrogen in the culture medium were increased. This study suggested a promising low-cost nonsterile PHB production strategy from organic wastes using strain ZD1.

Exogenous l-proline improved Rhodosporidium toruloides lipid production on crude glycerol

BACKGROUND

Crude glycerol as a promising feedstock for microbial lipid production contains several impurities that make it toxic stress inducer at high amount. Under stress conditions, microorganisms can accumulate l-proline as a safeguard. Herein, l-proline was assessed as an anti-stress agent in crude glycerol media.

RESULTS

Crude glycerol was converted to microbial lipids by the oleaginous yeast Rhodosporidium toruloides CGMCC 2.1389 in a two-staged culture mode. The media was supplied with exogenous l-proline to improve lipid production efficiency in high crude glycerol stress. An optimal amount of 0.5 g/L l-proline increased lipid titer and lipid yield by 34% and 28%, respectively. The lipid titer of 12.2 g/L and lipid content of 64.5% with a highest lipid yield of 0.26 g/g were achieved with l-proline addition, which were far higher than those of the control, i.e., lipid titer of 9.1 g/L, lipid content of 58% and lipid yield of 0.21 g/g. Similarly, l-proline also improved cell growth and glycerol consumption. Moreover, fatty acid compositional profiles of the lipid products was found suitable as a potential feedstock for biodiesel production.

CONCLUSION

Our study suggested that exogenous l-proline improved cell growth and lipid production on crude glycerol by R. toruloides. The fact that higher lipid yield as well as glycerol consumption indicated that l-proline might act as a potential anti-stress agent for the oleaginous yeast strain.

Investigation of fermentation conditions of biodiesel by-products for high production of β-farnesene by an engineered Escherichia coli

Recently, the research on conversion of biodiesel by-products to high value-added products has received much attention, due to the adverse effects of large accumulations of biodiesel by-products caused by the rapid increase in biodiesel production. Herein, this study investigated the utilization of by-products crude glycerol (CG-1 and CG-2) from two different industrial methods of biodiesel production and the favorable fermentation conditions for the high yield of β-farnesene by an engineered Escherichia coli F4, which harbored an optimized mevalonate pathway. Through analyzing by-products' components and fermentation performance, we found that CG-2 did not contain harmful impurities such as methanol and black solid impurities, and the β-farnesene production was up to 2.7 g/L from CG-2, which was similar to that from pure glycerol (2.5 g/L) and higher than that (2.21 g/L) from CG-1. Therefore, CG-2 was more suitable for β-farnesene production than CG-1, which might provide a reference for choosing a more suitable method on practical biodiesel production. Afterward, a variety of important fermentation conditions were explored using CG-2 as a substrate in shaken flasks. Under the optimal conditions (including induced cell density 1.0, initial cell density 0.25, temperature after induction 33 °C, initial medium pH 6.5), the yield of β-farnesene from CG-2 reached 10.31 g/L in a 5-L bioreactor, which was 2.8-fold higher than initial conditions in shake flasks and was the highest yield of β-farnesene produced from biodiesel by-products by fermentation as well. The recommended fermentation conditions in this work will provide a valuable reference for the industrial production of β-farnesene utilizing biodiesel by-products.

Two-Step Purification of Glycerol as a Value Added by Product From the Biodiesel Production Process

For every ton of biodiesel produced, about 100 kg of glycerol is also generated as a by-product. The traditional method of removing glycerol is mainly by gravity separation or centrifugation. This method generates crude glycerol, which may still contain impurities such as methanol, oil, soap, salt, and other organic materials at ppm levels. The effective usage of crude glycerol is important to improve the economic sustainability of the biodiesel industry while reducing the environmental impacts caused by the generated waste. The application and value of crude glycerol can be enhanced if these impurities are removed or minimized. Thus, it is important to develop a method which can increase the economic and applicable value of crude glycerol. Therefore, in the present study, the dual step purification method comprised of acidification and ion exchange techniques has been used to purify the crude glycerol and convert it into higher-value products. The acidification process started with the pH adjustment of the crude glycerol, using phosphoric acid to convert soap into fatty acid and salts. Then, the pretreated glycerol was further purified by ion exchange with a strong cation H⁺ resin. Gas chromatography (GC) was used to analyze both crude and purified glycerol and expressed as the weight percentage of glycerol content. A maximum glycerol purity of 98.2% was obtained after the dual step purification method at the optimized conditions of 60% of solvent, the flow rate of 15 mL/min and 40 g of resin. Further, the glycerol content measured being within the accepted amount of BS 2621:1979. Therefore, this study has proven that the proposed crude glycerol purification process is effective in improving the glycerol purity and could enhance the applicability of glycerol in producing value-added products which bring new revenue to the biodiesel industry.

Evaluation of 1,3-propanediol production by twoCitrobacter freundiistrains using crude glycerol and soybean cake hydrolysate

Biodiesel production processes using soybean as feedstock generates soybean cake and crude glycerol as by-products. These by-product streams were used as sole feedstocks for the production of 1,3-propanediol (PDO) using two bacterial strains of Citrobacter freundii. Soybean cake has been converted into a nutrient-rich hydrolysate by crude enzymes produced via solid state fermentation. The effect of initial glycerol and free amino nitrogen concentration on bacterial growth and PDO production has been evaluated in batch bioreactor cultures showing that C. freundii VK-19 is a more efficient PDO producer than C. freundii FMCC-8. The cultivation of C. freundii VK-19 in fed-batch bioreactor cultures using crude glycerol and soybean cake hydrolysates led to PDO concentration of 47.4 g/L with yield and productivity of 0.49 g/g and 1.01 g/L/h, respectively. The effect of PDO, metabolic by-products, and sodium and potassium salts on bacterial growth was evaluated showing that potassium salts initially enhance bacterial growth, whereas sodium salts cause significant inhibition to bacterial growth. Soybean cake hydrolysate and crude glycerol could be utilized for PDO production, but the fermentation efficiency is influenced by the catalyst used during biodiesel production.

Adaptability of Klebsiella pneumoniae 2e, a Newly Isolated 1,3-Propanediol-Producing Strain, to Crude Glycerol as Revealed by Genomic Profiling

Crude glycerol is largely generated as the main by-product of the biodiesel industry and is unprofitable for industrial application without costly purification. The direct bioconversion of crude glycerol into 1,3-propanediol (1,3-PDO) by microorganisms is a promising alternative for effective and economic utilization. In this study, Klebsiella pneumoniae 2e was newly isolated for the conversion of crude glycerol into 1,3-PDO. Batch fermentation analysis confirmed that crude glycerol and its main impurities had slight impacts on the growth, key enzyme activity, and 1,3-PDO production of K. pneumoniae 2e. The 1,3-PDO yield from crude glycerol by K. pneumoniae 2e reached 0.64 mol 1,3-PDO/mol glycerol, which was higher than that by most reported 1,3-PDO-producing Klebsiella strains. Genomic profiling revealed that K. pneumoniae 2e possesses 30 genes involved in glycerol anaerobic metabolism and 1,3-PDO biosynthesis. Quantitative real-time PCR analysis of these genes showed that the majority of the genes encoding the key enzymes for glycerol metabolism and 1,3-PDO biosynthesis were significantly upregulated during culture in crude glycerol relative to that in pure glycerol. Further comparative genomic analysis revealed a novel glycerol uptake facilitator protein in K. pneumoniae 2e and a higher number of stress response proteins than in other Klebsiella strains. This work confirms the adaptability of a newly isolated 1,3-PDO-producing strain, K. pneumoniae 2e, to crude glycerol and provides insights into the molecular mechanisms involved in its crude glycerol tolerance, which is valuable for industrial 1,3-PDO production from crude glycerol.IMPORTANCE The rapid development of the biodiesel industry has led to tremendous crude glycerol generation. Due to the presence of complex impurities, crude glycerol has low value for industry without costly purification. Obtaining novel microorganisms capable of direct and efficient bioconversion of crude glycerol to value-added products has great economic potential for industrial application. In this work, we characterized a newly isolated strain, Klebsiella pneumoniae 2e, with the capacity to efficiently produce 1,3-propanediol (1,3-PDO) from crude glycerol and demonstrated its adaptation to crude glycerol. Our work provides insights into the molecular mechanisms of K. pneumoniae 2e adaptation to crude glycerol and the expression patterns of its genes involved in 1,3-PDO biosynthesis, which will contribute to the development of industrial 1,3-PDO production from crude glycerol.

High-level production of short branched-chain fatty acids from waste materials by genetically modified Bacillus licheniformis

Short branched-chain fatty acids (SBCFAs) are multi-functional platform chemicals used in many fields. Currently, SBCFAs are produced mainly by chemical synthesis, which is high cost and lead to environmental pollution. The aim of this study was to achieve high-level production of SBCFAs from waste materials, bean dreg and crude glycerol. The Bacillus licheniformis DWc9n∗ was genetically modified by overexpression of SBCFAs synthesis genes via replacement of native promoter of bkd operon, the mutant strain DWc9n∗-PbacA produced 4.68 g/L of SBCFAs, increasing by 1.98-fold compared to wild-type strain. SBCFAs concentration was further increased to 7.85 g/L through process optimization. In a 5-L batch fermenter, the mutant showed SBCFAs production with high concentration (8.37 g/L) and productivity (0.20 g/L/h), which is the highest level of SBCFAs production based on low-value substrates fermentation. This is the first study describing efficient SBCFAs production by the modified B. licheniformis strain from bean dreg and crude glycerol.

Bioconversion of waste cooking oil glycerol from cabbage extract to lactic acid by Rhizopus microsporus

Glycerol from spent oil was processed by transesterification for biodiesel production. Although glycerol contains many types of impurities, it can be used as a C-source for lactic acid production by fungi, such as Rhizopus microsporus. In this study, we found that wild type R. microsporus (LTH23) produced more lactic acid than the mutant strains on cabbage glycerol media (CG media). More lactic acid was produced on CG media than on cabbage extract media (C media) by about two-fold in batch fermentation conditions. In addition, we found that lactic acid production in a fed-batch process was also slightly higher than in a batch process. To study the combined effects of pH, urea, and glycerol waste concentration on lactic acid production, a response surface methodology was used. The optimum pH, urea, and glycerol waste concentrations were pH 6.5, 3.75g/L, and 17g/L, respectively. The maximum lactic acid production predicted by this equation model was 4.03g/L.

Production of (Z)-11-(heptanoyloxy)undec-9-enoic acid from ricinoleic acid by utilizing crude glycerol as sole carbon source in engineered Escherichia coli expressing BVMO-ADH-FadL

Production of (Z)-11-(heptanoyloxy)undec-9-enoic acid from recinoleic acid was achieved by whole-cell biotransformation by Escherichia coli, utilizing crude glycerol as the sole carbon source. Whole-cell biotransformation resulted in ∼93% conversion of the substrate ricinoleic acid to (Z)-11-(heptanoyloxy)undec-9-enoic acid. We replaced the inducer-dependent promoter system (T7 and Rhm promotors) with a constitutive promoter system. This resulted in successful expression of ADH, FadL, and E6-BVMO, without costly inducer addition. Efficacy evaluation of the whole-cell biotransformation by inducer-free system by five different E. coli strains revealed that the highest product titer was accumulated in E. coli BW25113 strain. The engineered inducer-free system using crude glycerol as the sole carbon source showed competitive performance with induction systems. Optimized conditions resulted in the accumulation of 7.38 ± 0.42 mM (Z)-11-(heptanoyloxy)undec-9-enoic acid, and when 10 mM substrate was used as feed concentration, the product titer reached 2.35 g/L. The inducer-free construct with constitutive promoter system that this study established, which utilizes the waste by-product crude glycerol, will pave the way for the economic synthesis of many industrially important chemicals, like (Z)-11-(heptanoyloxy)undec-9-enoic acid.

Metabolic and proteomic analyses of product selectivity and redox regulation in Clostridium pasteurianum grown on glycerol under varied iron availability

BACKGROUND

Clostridium pasteurianum as an emerging new microbial cell factory can produce both n-butanol (BuOH) and 1,3-propanediol (1,3-PDO), and the pattern of product formation changes significantly with the composition of the culture medium. Among others iron content in the medium was shown to strongly affect the products selectivity. However, the mechanism behind this metabolic regulation is still unclear. For a better understanding of such metabolic regulation and for process optimization, we carried out fermentation experiments under either iron excess or iron limitation conditions, and performed metabolic, stoichiometric and proteomic analyses.

RESULTS

1,3-PDO is most effectively produced under iron limited condition (Fe-), whereas 1,3-PDO and BuOH were both produced under iron rich condition (Fe+). With increased iron availability the BuOH/1,3-PDO ratio increased significantly from 0.27 mol/mol (at Fe-) to 1.4 mol/mol (at Fe+). Additionally, hydrogen production was enhanced significantly under Fe+ condition. Proteomic analysis revealed differentiated expression of many proteins including several ones of the central carbon metabolic pathway. Among others, pyruvate: ferredoxin oxidoreductase, hydrogenases, and several electron transfer flavoproteins was found to be strongly up-regulated under Fe+ condition, pointing to their strong involvement in the regeneration of the oxidized form of ferredoxin, and consequently their influences on the product selectivity in C. pasteurianum. Of particular significance is the finding that H2 formation in C. pasteurianum is coupled to the ferredoxin-dependent butyryl-CoA dehydrogenase catalyzed reaction, which significantly affects the redox balance and thus the product selectivity.

CONCLUSIONS

The metabolic, stoichiometric and proteomic results clearly show the key roles of hydrogenases and ferredoxins dependent reactions in determining the internal redox balance and hence product selectivity. Not only the NADH pool but also the regulation of the ferredoxin pool could explain such product variation under different iron conditions.

Substrate dependent modulation of butanol to ethanol ratio in non-acetone forming Clostridium sporogenes NCIM 2918

Present study reports a non-acetone producing Clostridium sporogenes strain as a potential producer of liquid biofuels. Alcohol production was positively regulated by sorbitol and instant dry yeast as carbon and nitrogen sources respectively. Media optimization resulted in maximum butanol and ethanol titer (gL^-1) of 12.1 and 7.9 respectively. Depending on the combination of carbon sources, the organism was found to manipulate its metabolism towards synthesis of either ethanol or butanol, thereby affecting the total alcohol titer. Among various dual substrate combinations, glucose-glycerol mixture in the ratio of 60:40 resulted in maximum butanol and ethanol titer (gL^-1) of 11.9 and 12.1 respectively with total alcohol productivity of 0.59gL^-1h^-1. In the mixture, when pure glycerol was replaced with crude glycerol, butanol and ethanol titer (gL^-1) of 11.2 and 11.7 was achieved. Hence, the strain shows immense potential for biofuels production using crude glycerol as cheap substrate.

Genome-directed analysis of prophage excision, host defence systems, and central fermentative metabolism in Clostridium pasteurianum

Clostridium pasteurianum is emerging as a prospective host for the production of biofuels and chemicals, and has recently been shown to directly consume electric current. Despite this growing biotechnological appeal, the organism’s genetics and central metabolism remain poorly understood. Here we present a concurrent genome sequence for the C. pasteurianum type strain and provide extensive genomic analysis of the organism’s defence mechanisms and central fermentative metabolism. Next generation genome sequencing produced reads corresponding to spontaneous excision of a novel phage, designated φ6013, which could be induced using mitomycin C and detected using PCR and transmission electron microscopy. Methylome analysis of sequencing reads provided a near-complete glimpse into the organism’s restriction-modification systems. We also unveiled the chief C. pasteurianum Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) locus, which was found to exemplify a Type I-B system. Finally, we show that C. pasteurianum possesses a highly complex fermentative metabolism whereby the metabolic pathways enlisted by the cell is governed by the degree of reductance of the substrate. Four distinct fermentation profiles, ranging from exclusively acidogenic to predominantly alcohologenic, were observed through redox consideration of the substrate. A detailed discussion of the organism’s central metabolism within the context of metabolic engineering is provided.

Production of carotenoids and lipids by Rhodococcus opacus PD630 in batch and fed-batch culture

Production of carotenoids by Rhodococcus opacus PD630 is reported. A modified mineral salt medium formulated with glycerol as an inexpensive carbon source was used for the fermentation. Ammonium acetate was the nitrogen source. A dry cell mass concentration of nearly 5.4 g/L could be produced in shake flasks with a carotenoid concentration of 0.54 mg/L. In batch culture in a 5 L bioreactor, without pH control, the maximum dry biomass concentration was ~30 % lower than in shake flasks and the carotenoids concentration was 0.09 mg/L. Both the biomass concentration and the carotenoids concentration could be raised using a fed-batch operation with a feed mixture of ammonium acetate and acetic acid. With this strategy, the final biomass concentration was 8.2 g/L and the carotenoids concentration was 0.20 mg/L in a 10-day fermentation. A control of pH proved to be unnecessary for maximizing the production of carotenoids in this fermentation.

Activation of glycerol metabolism in Xanthomonas campestris by adaptive evolution to produce a high-transparency and low-viscosity xanthan gum from glycerol

Many studies have focused on using crude glycerol from biodiesel to obtain valuable products, but few of these studies have focused on obtaining polysaccharides. A mutant strain of Xanthomonas campestris CCTCC M2015714 that could use glycerol to produce high-transparency and low-viscosity xanthan gum was obtained by adaptive evolution, and the yield of xanthan gum reached 11.0g/L. We found that transcriptional levels of genes related to glycerol metabolism (glpF, glpK, glpD, and fbp) in the mutant strain were all higher than those from the parent strain. Using 5g/L sucrose or glucose as starter substrate, cell growth time decreased from 36h to 24h and xanthan gum yield increased. Moreover, the mutant strain can tolerate high titer glycerol, and its activity was not affected by the impurities in crude glycerol. All these results proved that crude glycerol from biodiesel industries can be used for xanthan gum production.

Engineering membrane and cell-wall programs for tolerance to toxic chemicals: Beyond solo genes

Metabolite toxicity in microbes, particularly at the membrane, remains a bottleneck in the production of fuels and chemicals. Under chemical stress, native adaptation mechanisms combat hyper-fluidization by modifying the phospholipids in the membrane. Recent work in fluxomics reveals the mechanism of how membrane damage negatively affects energy metabolism while lipidomic and transcriptomic analyses show that strains evolved to be tolerant maintain membrane fluidity under stress through a variety of mechanisms such as incorporation of cyclopropanated fatty acids, trans-unsaturated fatty acids, and upregulation of cell wall biosynthesis genes. Engineered strains with modifications made in the biosynthesis of fatty acids, peptidoglycan, and lipopolysaccharide have shown increased tolerance to exogenous stress as well as increased production of desired metabolites of industrial importance. We review recent advances in elucidation of mechanisms or toxicity and tolerance as well as efforts to engineer the bacterial membrane and cell wall.

The role of 1,3-propanediol production in fermentation of glycerol by Clostridium pasteurianum

Waste crude glycerol from biodiesel production can be used to produce biobutanol using Clostridium pasteurianum with the main products being n-butanol, 1,3-propanediol (PDO) and ethanol. There has been much discrepancy and mystery around the cause and effect of process parameters on the product distribution, thus a better understanding of the pathway regulation is required. This study shows that as process pH decreased, the rate of cell growth and CO2 production also decreased, resulting in slower fermentations, increased duration of butanol production and higher butanol concentrations and yields. The production rate of PDO was multi-modal and the role of PDO appears to function in redox homeostasis. The results also showed that C. pasteurianum displayed little biphasic behavior when compared to Clostridia spp. typically used in ABE fermentation due to the alternative glycolysis-independent reductive pathway of PDO production, rendering it suitable for a continuous fermentation process.

Cooperative effects of fatty acids and n-butanol on lipid membrane phase behavior

Biodiesel-derived crude glycerol can be fermented to produce n-butanol, which is a platform chemical for biorefining and a biofuel. One limitation to crude glycerol fermentation is the presence of long-chain fatty acids (FAs) that can partition into cellular membranes, leading to membrane fluidization and interdigitation, which can inhibit cellular function. In this work, we have examined the phase behavior of dipalmitoylphosphatidylcholine (DPPC, C16:0) membranes and the membrane partitioning of n-butanol as a function of FA degree of unsaturation (steric, oleic, and linoleic acids) using differential scanning calorimetry (DSC) and monolayer surface pressure studies. All three FAs at 15mol% (85mol% DPPC) prevented interdigitation by n-butanol based on the DSC results. n-Butanol partitioning and membrane expansion was greatest for DPPC/oleic acid membranes, where monounsaturated oleic acid (OA, C18:1) was miscible in gel and fluid phase DPPC. Saturated steric acid (SA, C18:0), which ordered the membranes and yielded a SA-rich phase during melting, led to a modest increase in n-butanol partitioning compared to DPPC alone. Di-unsaturated linoleic acid (LA, C18:2), which disordered the membranes and phase separated, had little affect on n-butanol partitioning into the DPPC-rich phases. The effects of OA and LA are attributed to the additional interfacial area provided by these FAs due to acyl tail 'kinks' at the carbon double bonds. These results show that exogenous FAs can partition into membranes, impacting n-butanol partitioning and acting cooperatively with n-butanol to alter membrane structure.

Effective production of low crystallinity Poly(3-hydroxybutyrate) by recombinant E. coli strain JM109 using crude glycerol as sole carbon source

Utilization of bio-diesel by-products (glycerol) for microbial polymer production has created a novel biorefinery concept. In the present study, recombinant Escherichia coli JM109 was used for the production of P(3 HB) from glycerol as carbon source. Batch fermentation in a 7.5L bioreactor with the statistically optimized culture condition (pre-treated glycerol: 27.5 g/L and casein hydrolysate: 5.25 g/L) scaled up the P3HB production to 65% (∼ 8 g/L). FTIR, (1)H and (13)C NMR analysis proved the polymer produced to be P(3 HB). Gel permeation chromatography, Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) demonstrated the produced P(3 HB) to have high molecular weight (2.84 × 10(6)) and lowered crystallinity (∼ 30%) compared to commercial polymer. Integrating the production efficiency and the thermal characteristics of the polymer produced by recombinant E. coli, the viability and sustainability of biofuels and biopolymers for economic human need could be enhanced.

Whole-genome sequence of an evolved Clostridium pasteurianum strain reveals Spo0A deficiency responsible for increased butanol production and superior growth

BACKGROUND

Biodiesel production results in crude glycerol waste from the transesterification of fatty acids (10 % w/w). The solventogenic Clostridium pasteurianum, an anaerobic Firmicute, can produce butanol from glycerol as the sole carbon source. Coupling butanol fermentation with biodiesel production can improve the overall economic viability of biofuels. However, crude glycerol contains growth-inhibiting byproducts which reduce feedstock consumption and solvent production.

RESULTS

To obtain a strain with improved characteristics, a random mutagenesis and directed evolution selection technique was used. A wild-type C. pasteurianum (ATCC 6013) culture was chemically mutagenized, and the resulting population underwent 10 days of selection in increasing concentrations of crude glycerol (80-150 g/L). The best-performing mutant (M150B) showed a 91 % increase in butanol production in 100 g/L crude glycerol compared to the wild-type strain, as well as increased growth rate, a higher final optical density, and less production of the side product PDO (1,3-propanediol). Wild-type and M150B strains were sequenced via Single Molecule Real-Time (SMRT) sequencing. Mutations introduced to the M150B genome were identified by sequence comparison to the wild-type and published closed sequences. A major mutation (a deletion) in the gene of the master transcriptional regulator of sporulation, Spo0A, was identified. A spo0A single gene knockout strain was constructed using a double--crossover genome-editing method. The Spo0A-deficient strain showed similar tolerance to crude glycerol as the evolved mutant strain M150B. Methylation patterns on genomic DNA identified by SMRT sequencing were used to transform plasmid DNA to overcome the native C. pasteurianum restriction endonuclease.

CONCLUSIONS

Solvent production in the absence of Spo0A shows C. pasteurianum differs in solvent-production regulation compared to other solventogenic Clostridium. Growth-associated butanol production shows C. pasteurianum to be an attractive option for further engineering as it may prove a better candidate for butanol production through continuous fermentation.

Effect of 1,3-propanediol, organic acids, and ethanol on growth and metabolism of Clostridium butyricum DSP1

Knowledge of tolerance of bacteria to toxic stress is important, especially for processes targeted at high final titers of product. Information on environmental limits and stress responses may help during selection of strains or design and control of processes. The influence of the main product and its co-products on the process of 1,3-propanediol (PD) synthesis was determined. Adaptation to toxic compounds was noticed as Clostridium butyricum DSP1 was less sensitive to the addition of these factors during its exponential growth on glycerol than when the factor was present in the medium before inoculation. It was also shown that the response of the tested strain to the toxicity of 1,3-propanediol (1,3-PD) has different proteomic profiles depending on the stage of culture when this substance is introduced. Relatively satisfactory activity of the analyzed strain was sustained up to a concentration of 1,3-PD of 40 g/L while 80 g/L of this metabolite was lethal to the bacterium. As for the by-products, acetic acid was determined to be the most toxic among the acids excreted during the process.

In vitro conversion of glycerol to lactate with thermophilic enzymes

Background

In vitro reconstitution of an artificial metabolic pathway has emerged as an alternative approach to conventional in vivo fermentation-based bioproduction. Particularly, employment of thermophilic and hyperthermophilic enzymes enables us a simple preparation of highly stable and selective biocatalytic modules and the construction of in vitro metabolic pathways with an excellent operational stability. In this study, we designed and constructed an artificial in vitro metabolic pathway consisting of nine (hyper)thermophilic enzymes and applied it to the conversion of glycerol to lactate. We also assessed the compatibility of the in vitro bioconversion system with methanol, which is a major impurity in crude glycerol released from biodiesel production processes.

Results

The in vitro artificial pathway was designed to balance the intrapathway consumption and regeneration of energy and redox cofactors. All enzymes involved in the in vitro pathway exhibited an acceptable level of stability at high temperature (60°C), and their stability was not markedly affected by the co-existing of up to 100 mM methanol. The one-pot conversion of glycerol to lactate through the in vitro pathway could be achieved in an almost stoichiometric manner, and 14.7 mM lactate could be produced in 7 h. Furthermore, the in vitro bioconversion system exerted almost identical performance in the presence of methanol.

Conclusions

Many thermophilic enzymes exhibit higher stability not only at high temperatures but also in the presence of denaturants such as detergents and organic solvents than their mesophilic counterparts. In this study, compatibilities of thermophilic enzymes with methanol were demonstrated, indicating the potential applicability of in vitro bioconversion systems with thermophilic enzymes in the conversion of crude glycerol to value-added chemicals.

Biotechnological potential of Clostridium butyricum bacteria

In response to demand from industry for microorganisms with auspicious biotechnological potential, a worldwide interest has developed in bacteria and fungi isolation. Microorganisms of interesting metabolic properties include non-pathogenic bacteria of the genus Clostridium, particularly C. acetobutylicum, C. butyricum and C. pasteurianum. A well-known property of C. butyricum is their ability to produce butyric acid, as well as effectively convert glycerol to 1,3-propanediol (38.2 g/L). A conversion rate of 0.66 mol 1,3-propanediol/mol of glycerol has been obtained. Results of the studies described in the present paper broaden our knowledge of characteristic features of C. butyricum specific isolates in terms of their phylogenetic affiliation, fermentation capacity and antibacterial properties.

Rapid and reliable method for identification of associated endonuclease cleavage and recognition sites

One barrier to cross during genetic engineering is the restriction-modification system found in many bacteria. In this study, we developed a fast and reliable method for mapping the recognition and cleavage site of the restriction endonucleases. Clostridium pasteurianum, a model organism for the study of nitrogen fixation, has been found to harbour at least two restriction-modification systems including the restriction endonucleases CpaPI, which is an isoschizomer of MboI and CpaAI. Dam-methylated DNA was used to isolate the activity of CpaAI. Exposing freshly prepared cell lysate to known nucleotide fragments and directly sequencing the pool of digested nucleotide fragments enabled identification of the cleavage sites in the fragments. By aligning the sequences adjacent to the cleavage site, it was possible to identify the recognition sequence. Using this method, we successfully located all CpaAI recognition and cleavage sites within the template sequence. By modifying DNA with both Dam and CpG methylases (M.SssI) and thereby preventing digestion by CpaPI and CpaAI, no further endonuclease activity was detected.

SIGNIFICANCE AND IMPACT OF THE STUDY

Restriction-modification systems are important barriers to successful genetic modification in many bacterial species. In this study, we demonstrate an efficient and general applicable method for identifying endonuclease recognition and cleavage sites. For the study and the trails, the model organism for nitrogen fixation Clostridium pasteurianum was used. The method was proven to be reliable, and by modifying DNA at the identified sites, it is possible to prevent digestion.