Glycerol Utilization Research Articles

AMPK Is Involved in Regulating the Utilization of Carbon Sources, Conidiation, Pathogenicity, and Stress Response of the Nematode-Trapping Fungus Arthrobotrys oligospora.

ABSTRACTAMP-activated protein kinase (AMPK), a heterotrimeric complex, can sense energy and nutritional status in eukaryotic cells, thereby participating in the regulation of multiple cellular processes. In this study, we characterized the function of the catalytic α-subunit (SNF1) and the two regulatory β- and γ-subunits (GAL83 and SNF4) of AMPK in a representative nematode-trapping fungus, Arthrobotrys oligospora, by gene knockout, phenotypic analysis, and RNA sequencing. The ability of the AMPK complex mutants (including ΔAosnf1, ΔAogal83, and ΔAosnf4) to utilize a nonfermentable carbon source (glycerol) was reduced, and the spore yields and trap formation were remarkably decreased. Moreover, AMPK plays an important role in regulating stress response and nematode predation efficiency. Transcriptomic profiling between the wild-type strain and ΔAosnf1 showed that differentially expressed genes were enriched for peroxisome, endocytosis, fatty acid degradation, and multilipid metabolism (sphingolipid, ether lipid, glycerolipid, and glycerophospholipid). Meanwhile, a reduced lipid droplet accumulation in ΔAosnf1, ΔAogal83, and ΔAosnf4 mutants was observed, and more vacuoles appeared in the mycelia of the ΔAosnf1 mutant. These results highlight the important regulatory role of AMPK in the utilization of carbon sources and lipid metabolism, as well as providing novel insights into the regulatory mechanisms of the mycelia development, conidiation, and trap formation of nematode-trapping (NT) fungi.IMPORTANCE NT fungi are widely distributed in various ecosystems and are important factors in the control of nematode populations in nature; their trophic mycelia can form unique infectious devices (traps) for capturing nematodes. Arthrobotrys oligospora is a representative NT fungi which can develop complex three-dimensional networks (adhesive networks) for nematode predation. Here, we demonstrated that AMPK plays an important role in the glycerol utilization, conidiation, trap formation, and nematode predation of A. oligospora, which was further confirmed by transcriptomic analysis of the wild-type and mutant strains. In particular, our analysis indicated that AMPK is required for lipid metabolism, which is primarily associated with energy regulation and is essential for trap formation. Therefore, this study extends the functional study of AMPK in NT fungi and helps to elucidate the molecular mechanism of the regulation of trap development, as well as laying the foundation for the development of efficient nematode biocontrol agents.

Glycerol steam reforming over hydrothermal synthetic Ni-Ca/attapulgite for green hydrogen generation

• Glycerol steam reforming over hydrothermal synthetic Ni-Ca/ATP was firstly studied. • Effect of Ca content and preparation method on Ni/ATP structure was investigated. • Hydrothermal synthesis ( hs ) enhanced the distribution of Ca and Ni species over ATP. • Ni-6Ca/ATP- hs had strong CO 2 adsorption and abundant Ni-CaO x interfaces. • Ni-6Ca/ATP- hs exhibited superior performance and sinter/coke durability for GSR. Glycerol steam reforming (GSR) is one of the promising technologies that can realize renewable hydrogen production and efficient utilization of crude glycerol. To illuminate the functions of Ca content (3%, 6%, 9%, and 12%, by mass) and preparation method for Ni/ATP catalyst structure and its catalytic behaviors, the Ni- x Ca/ATP ( x = 3%, 6%, 9%, and 12%, by mass) catalysts are prepared by co-impregnation ( ci ) and hydrothermal synthesis ( hs ) method and then tested in GSR. Characterization results of XRD, N 2 adsorption–desorption, H 2 -TPR, HRTEM, XPS, and NH 3 /CO 2 -TPD demonstrate that the combined effect between appropriate Ca additive (6%, by mass) and hs enhance catalyst reducibility, uniform distribution of Ca additive and nickel species over ATP, and adsorption for CO 2 . This attributes to hs method protects the ATP framework through suppressing the interaction of Ca with ATP and promotes the formation of Ni-CaO x interface sites. Therefore, Ni-6Ca/ATP- hs exhibits the highest conversion (86.77%) of glycerol to gas product and H 2 yield (76.17%) and selectivity (58.56%) during GSR. Furthermore, XRD, HRTEM, TG-DTG and Raman analyses confirm that Ni-6Ca/ATP- hs also reveals outstanding anti-sintering and coke resistance. In addition, the structural evolution process of Ni/ATP catalyst with Ca introduction and hs method is presented. Considering the high performance, simple preparation process and low cost, the as-prepared catalyst providing new opportunities for utilization of glycerol derived from biodiesel industry.

Recent advances in the utilization of glycerol for the production of lactic acid by catalysis

AbstractIn this review, the research progress on catalytic conversion of glycerol to lactic acid or lactate esters and the reaction mechanisms with different catalysis systems are summarized. Both homogeneous catalysts, including inorganic bases and metal complexes, and heterogeneous catalysts, including metal oxides, molecular sieves, polyoxometalates and noble and non‐noble metals, are discussed. In particular, the influence of catalyst components, the physical and chemical properties of the catalysts and additives and solvents on the catalytic performances are highlighted. In comparison, nano‐metal particles or bimetal catalysts could achieve good catalytic performance, in which the alloy and synergistic effects might form under certain conditions. For further improvement of the sustainable transformation of glycerol to lactic acid or lactate esters, attention should still be paid to rational design of novel cost‐effective, high‐efficiency and green catalytic systems. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Glycerol Utilization as a Sole Carbon Source Disrupts the Membrane Architecture and Solventogenesis in Clostridium beijerinckii NCIMB 8052

Efficient bioconversion of abundant waste glycerol to value-added chemicals calls for a wider range of fermentative workhorses that can catabolize glycerol. In this study, we used quantitative gene expression and solvent profiling, qualitative metabolite analysis, and enzyme activity assays to investigate the factors that limit glycerol utilization as a sole carbon source by Clostridium beijerinckii NCIMB 8052. C. beijerinckii NCIMB 8052 did not produce acetate, acetone and butanol on glycerol. Congruently, the genes encoding the coenzyme A transferase subunits (ctfAB) and bifunctional acetaldehyde-CoA/alcohol dehydrogenase (adhE) were down-regulated up to 135- and 21-fold, respectively, at 12 h in glycerol-grown cells compared to glucose-grown cells. Conversely, NADH-dependent butanol dehydrogenase A (bdhA) was upregulated 2-fold. Glycerol dehydrogenase (gldA) and dihydroxyacetone kinase (subunit dhaK) were upregulated up to 5- and 881-fold, respectively. Glyceraldehyde-3-phosphate dehydrogenase (gapdh) showed mostly similar expression profiles at 12 h on glucose and glycerol. At 24 h, gapdh was downregulated 1.5-fold, while NADP+-dependent gapdh was upregulated up to 1.9-fold. Glycerol-grown cells showed higher or similar activity profiles for all solventogenic enzymes studied, compared to glucose-grown cells. Butyraldehyde (3 g/L) supplementation led to the production of ~0.1 g/L butanol, whilst butyrate (3.5 g/L) supplementation produced 0.7 and 0.5 g/L acetone and butanol, respectively, with glycerol. Further, the long chain saturated fatty acids cyclopentaneundecanoic acid, methyl ester and hexadecanoic acid, butyl ester were detected in glucose- but not in glycerol-grown cells. Collectively, growth on glycerol appears to disrupt synthesis of saturated long chain fatty acids, as well as solventogenesis in C. beijerinckii NCIMB 8052.

Screening of xylose utilizing and high lipid producing yeast strains as a potential candidate for industrial application

BackgroundSustainable production of oil for food, feed, fuels and other lipid-based chemicals is essential to meet the demand of the increasing human population. Consequently, novel and sustainable resources such as lignocellulosic hydrolysates and processes involving these must be explored. In this paper we screened for naturally-occurring xylose utilizing oleaginous yeasts as cell factories for lipid production, since pentose sugar catabolism plays a major role in efficient utilization of lignocellulosic feedstocks. Glycerol utilization, which is also beneficial in yeast-based oil production as glycerol is a common by-product of biodiesel production, was investigated as well. Natural yeast isolates were studied for lipid accumulation on a variety of substrates, and the highest lipid accumulating strains were further investigated in shake flask cultivations and fermenter studies on xylose and hydrolysate.ResultsBy collecting leaves from exotic plants in greenhouses and selective cultivation on xylose, a high frequency of oleaginous yeasts was obtained (> 40%). Different cultivation conditions lead to differences in fatty acid contents and compositions, resulting in a set of strains that can be used to select candidate production strains for different purposes. In this study, the most prominent strains were identified as Pseudozyma hubeiensis BOT-O and Rhodosporidium toruloides BOT-A2. The fatty acid levels per cell dry weight after cultivation in a nitrogen limited medium with either glucose, xylose or glycerol as carbon source, respectively, were 46.8, 43.2 and 38.9% for P. hubeiensis BOT-O, and 40.4, 27.3 and 42.1% for BOT-A2. Furthermore, BOT-A2 accumulated 45.1% fatty acids per cell dry weight in a natural plant hydrolysate, and P. hubeiensis BOT-O showed simultaneous glucose and xylose consumption with similar growth rates on both carbon sources. The fatty acid analysis demonstrated both long chain and poly-unsaturated fatty acids, depending on strain and medium.ConclusionsWe found various natural yeast isolates with high lipid production capabilities and the ability to grow not only on glucose, but also xylose, glycerol and natural plant hydrolysate. R. toruloides BOT-A2 and P. hubeiensis BOT-O specifically showed great potential as production strains with high levels of storage lipids and comparable growth to that on glucose on various other substrates, especially compared to currently used lipid production strains. In BOT-O, glucose repression was not detected, making it particularly desirable for utilization of plant waste hydrolysates. Furthermore, the isolated strains were shown to produce oils with fatty acid profiles similar to that of various plant oils, making them interesting for future applications in fuel, food or feed production.

Utilization of Natural Dyes Solutions and Glycerol for the Quality and Durability of Direct Wet Mount Preparations Storage in Educational Laboratories

Educational laboratories require the availability of direct wet mount preparations that can last a long time with good quality. Various studies have mentioned techniques so that preparations can last a long time. This study aims to analyze the composition of dyes and glycerol in wet preparations of worm eggs on the quality and shelf life of the preparations. The solvent variations used for the wet preparations were Angkak 2%, and eosin 2%, with the addition of variations in the concentration of glycerol 20%-45%. The number of treatments and repetitions in the study was 70 samples, which were observed in the first, second, third, and fourth weeks. Based on the ANOVA test, the results showed a significant effect on the parameters measured, namely the type of dye, the type of slide, and the shelf life of the preparation (storage) in natural dye solution (2% ethanol extract of Angkak solution) and synthetic dye solution (2% eosin solution). The correlation test results of storage time treatment on the clarity of the preparations showed that the longer the storage, the lower the clarity of the preparations (r=-0.46246). The correlation test results of storage time treatment on the contrast of the preparations showed that the longer the storage, the less the contrast was not so strong (r=-0.26375). The correlation test results of storage time treatment on the quality of the preparations showed that the longer the storage, the lower the quality of the preparations (r=-0.51346). The conclusion is that the best quality of wet preparations is preparations that are stored for four weeks using a flat object-glass with a mixture of 1:1 dye solution of 2%-glycerol solution of 35% and 1:1 mixture of a 2%-glycerol solution of 1:1 solution. Further research is needed on the concentration of the dye solution mixture to find the best formulation for improving the quality and resistance of wet preparations.

Estimation of Carbon Metabolism in Saccharomyces cerevisiae Acclimatized to Glycerol Assimilation with Quantitative PCR.

Saccharomyces cerevisiae has the potential to produce value-added chemicals; however, this strain is restricted by using glycerol as a carbon source. Although acclimatization of S. cerevisiae as a glycerol-assimilating strain was confirmed so far, the reason why S. cerevisiae can be acclimatized was not clear in detail with limited information on the metabolic changes. In this report, glycerol-assimilating strains from S. cerevisiae BY4741 were isolated, and the biomass production, ethanol fermentation, and transcription levels related to glycolysis and the tricarboxylic acid cycle under aerobic and slightly anaerobic conditions were analyzed. As the results show, although µmax was equal to 0.15 h−1 between wildtype and glycerol-assimilating strains in an aerobic culture including glucose, the differences in max biomass production and percentage yields of ethanol and transcription levels between the two strains were shown. In slightly anaerobic culture, the differences in transcription levels downstream of glycolysis were also displayed. In the case of the glycerol-assimilating strain with glycerol under aerobic conditions, although the transcription levels related to ethanol production were sufficient, the ethanol production was not detected. Additionally, the biomass production reached a plateau even in the culture containing sufficient glycerol, indicating that the redox imbalance even in the cells of the glycerol-acclimatized strain could disturb the utilization of glycerol. The obtained knowledge will promote the use of glycerol resources with the glycerol-acclimatized S. cerevisiae in view of carbon recycling.

Metabolic engineering of Komagataella phaffii for synergetic utilization of glucose and glycerol.

Komagataella phaffii GS115 is a proven heterologous expression system and has recently been exploited for the production of value-added biochemicals from glucose through metabolic engineering. A major challenge for high-level biochemical production is the appropriate distribution of carbon flux between cell growth and product biosynthesis. In this study, we report the development of a synergetic glucose and glycerol coutilization strategy for K. phaffii, potentially enabling this strain to consume glycerol for growth while conserving more glucose for product formation. First, several potential genes encoding mediator proteins and transcriptional factors that were considered to be associated with carbon catabolite repression in K. phaffii were screened, and deletion of gss1, a glucose sensor, appeared to be able to eliminate the glucose-induced repression of glycerol utilization in a mixed glucose-glycerol medium. Transcriptome comparisons between the parent strain and the Δgss1 mutant were then performed, and the glycerol-metabolism genes that were subjected to glucose regulation were identified. Second, coutilization of glucose and glycerol in K. phaffii was achieved by overexpressing genes relevant to glycerol metabolism, namely, gt1, gut1, and gut2. Furthermore, knockout or knockdown of pfk and zwf genes resulted in a reduction of carbon flux from glucose towards glycolysis and the pentose phosphate pathway. With these efforts, the cell metabolism of the final strain was divided into growth and production modules. This study describes a promising strategy to address the challenge of carbon flux distribution in K. phaffii, and would be valuable in engineering this strain as a versatile fermentation platform for biochemical production.

Systematic engineering of Bacillus amyloliquefaciens for efficient production of poly-γ-glutamic acid from crude glycerol

Microbial production of poly-γ-glutamic acid (γ-PGA) from non-food raw materials is a promising alternative to food feedstocks-based biosynthesis. A superior cell factory of Bacillus amyloliquefaciens for the efficient synthesis of γ-PGA from crude glycerol was constructed through systematic metabolic engineering. Firstly, some phase-dependent promoters were screened from B. amyloliquefaciens, which can be used for fine regulation of subsequent metabolic pathways. Secondly, the glycerol utilization pathway and the γ-PGA synthesis pathway were co-optimized utilizing the above-screened promoters, which increased the titer of γ-PGA by 1.75-fold. Then, the titer of γ-PGA increased to 15.6 g/L by engineering transcription factors degU and blocking competitive pathways. Finally, combining these strategies with an optimized fermentation process, 26.4 g/L γ-PGA was obtained from crude glycerol as a single carbon source (a 3.72-fold improvement over the initial strain). Overall, these strategies will have great potential for synthesizing other products from crude glycerol in B. amyloliquefaciens.

Engineering of a thermophilic dihydroxy-acid dehydratase toward glycerate dehydration for in vitro biosystems.

Dihydroxy-acid dehydratase (DHAD) plays an important role in the utilization of glycerol or glucose for the production of value-added chemicals in the in vitro synthetic enzymatic biosystem. The low activity of DHAD in the dehydration of glycerate to pyruvate hampers its applications in biosystems. Protein engineering of a thermophilic DHAD from Sulfolobus solfataricus (SsDHAD) was performed to increase its dehydration activity. A triple mutant (I161M/Y145S/G205K) with a 10-fold higher activity on glycerate dehydration was obtained after three rounds of iterative saturation mutagenesis (ISM) based on computational analysis. The shrunken substrate-binding pocket and newly formed hydrogen bonds were the reason for the activity improvement of the mutant. For the in vitro synthetic enzymatic biosystems of converting glucose or glycerol to L-lactate, the biosystems with the mutant SsDHAD showed 3.32- and 2.34-fold higher reaction rates than the wild type, respectively. This study demonstrates the potential of protein engineering to improve the efficiency of in vitro synthetic enzymatic biosystems by enhancing the enzyme activity of rate-limited enzymes. KEY POINTS: • A screening method was established for the protein engineering of SsDHAD. • A R3 mutant of SsDHAD with 10-fold higher activity was obtained. • The R3 mutant exhibits higher productivity in the in vitro biosystems.

Production and characterization of polyhydroxybutyrate (PHB) BY Burkholderia cepacia BPT1213 using waste glycerol as carbon source

This study focused on the utilization of waste glycerol, a by-product of the biodiesel industry, used as a carbon source to grow Burkholderia cepacia BPT1213 for the production of PHB. B. cepacia BPT1213 was cultivated in minimal salt media (MSM) supplemented with waste glycerol at concentrations ranging from 2% to 9% (v/v). A gradual decrease was depicted by the cell dry weight (CDW) and PHB content with increasing waste glycerol content. B. cepacia BPT1213 is able to synthesize and accumulate up to 2.41 g/L and 66.4% dry biomass and PHB yield respectively when supplemented with 2% (v/v) waste glycerol. This resulted in a total PHB concentration of 1.6 g/L. The characterization of extracted PHB was carried out by Nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) for structural composition evaluation. Both analyses showed expected signals for PHB as reported in other studies which depicted the methyl, methylene and methine groups for NMR analyses, and certain functional groups which were the hydroxyl group, carbonyl stretch and ester group for FTIR. This study demonstrated the effects of waste glycerol concentration on the end properties of PHB, which is an important aspect for its applications.

On the Utilization of Dietary Glycerol in Carnivorous Fish - Part I: Insights Into Hepatic Carbohydrate Metabolism of Juvenile Rainbow Trout (Oncorhynchus mykiss) and European Seabass (Dicentrarchus labrax)

Glycerol is a 3-carbon sugar alcohol successfully employed as an alternative feed ingredient for land-farmed animals and more recently for farmed fish. While most studies address zootechnical performance, few have delved into the metabolic utilization of dietary glycerol. A growth trial was performed using diets with increasing levels of glycerol (0, 2.5 and 5%) on two relevant species for aquaculture: rainbow trout (8-week trial; 3 tank per diet/25 fish per tank, on a 15 ± 1°C flow-through freshwater system); and European seabass (6-week trial; 5 tank per diet/6-8 fish per tank on a 21°C indoor saltwater RAS system). After this period, fish were subjected to a metabolic trial consisting of a 6-day residence in deuterated water (2H2O). Measurements of blood glucose and hepatic glycogen 2H-enrichments through Nuclear Magnetic Resonance, complemented by mRNA levels of key-enzymes for intermediary metabolism were used to evaluate the catabolic pathways of dietary glycerol. Dietary glycerol had no impact on plasma glucose, but hepatic glycogen levels increased significantly with increasing dietary glycerol levels in both species. While trout was able to regulate circulating glycerol plasma, seabass presented elevated levels on the glycerol-supplemented diets. Despite revealing some significant differences between sampling time (6 and 24 h), none of the enzymes’ mRNA levels responded to the dietary treatment. In trout, the main source of blood glucose was not labeled with 2H (~60%, likely from diet) while other contributors did not differ with glycerol supplementation. In seabass, the unlabeled contribution was approximately half of that observed in trout (~30%), accompanied by a significant increase of gluconeogenic contributions at the triose-phosphate level to the blood glucose with increasing dietary glycerol. In trout, labeling from 2H2O into hepatic glycogen revealed significant differences, with the contribution from the indirect pathway at the triose-phosphate level increasing with increased dietary glycerol. No such differences were found in seabass’ glycogen pool. These findings suggest that fish species are able to retain, catabolize glycerol and incorporate it into carbohydrates. The gluconeogenic utilization of exogenous glycerol differed between species and affected the synthesis of hepatic glycogen in trout and the appearance of blood glucose in seabass.

Glycerol as an excellent hydrogen and electron source for photocatalytic hydrogenation of nitrobenzene in water

The development of a new method for effective utilization of glycerol dissolved in water is needed. In this study, glycerol was used not as an energy source and a starting compound but as an electron and hydrogen source for photocatalytic hydrogenation of nitrobenzene in an aqueous suspension of TiO2 under various conditions. The function of glycerol as an electron and hydrogen source was compared with that of other C3-alcohols and glycols. The results showed that glycerol works most efficiently as an electron and hydrogen source and that electrons extracted from glycerol are directly used for the hydrogenation without formation of other products such as H2. The photocatalytic hydrogenation was also examined under solar light with and without stirring. Important factors for the electron and hydrogen source in the photocatalytic reaction in an aqueous medium are discussed on the basis of the results.

The reliance of glycerol utilization by Cupriavidus necator on CO2 fixation and improved glycerol catabolism

While crude glycerol is a cheap carbon source for industrial-scale cultivation of microorganisms, its application relies on fast growth and conversion. The biopolymer producing Cupriavidus necator H16 (synonym: Ralstonia eutropha H16) grows poorly on glycerol. The heterologous expression of glycerol facilitator glpF, glycerol kinase glpK, and glycerol dehydrogenase glpD from E. coli accelerated the growth considerably. The naturally occurring glycerol utilization is inhibited by low glycerol kinase activity. A limited heterotrophic growth promotes the dependency on autotrophic growth by carbon dioxide (CO2) fixation and refixation. As mixotrophic growth occurs in the wildtype due to low consumption rates of glycerol, CO2 fixation by the Calvin-Benson-Bassham (CBB) cycle is essential. The deletion of both cbbX copies encoding putative RuBisCO-activases (AAA + ATPase) resulted in a sharp slowdown of growth and glycerol consumption. Activase activity is necessary for functioning carboxylation by RuBisCO. Each of the two copies compensates for the loss of the other, as suggested by observed expression levels. The strong tendency towards autotrophy supports previous investigations of glycerol growth and emphasizes the versatility of the metabolism of C. necator H16. Mixotrophy with glycerol-utilization and CO2 fixation with a high dependence on the CBB is automatically occurring unless transportation and degradation of glycerol are optimized. Parallel engineering of CO2 fixation and glycerol degradation is suggested towards application for value-added production from crude glycerol. KEY POINTS: • Growth on glycerol is highly dependent on efficient carbon fixation via CBB cycle. • CbbX is essential for the efficiency of RuBisCO in C. necator H16. • Expression of glycerol degradation pathway enzymes accelerates glycerol utilization.

Utilization of Different Carbon Sources by Nordic Microalgae Grown Under Mixotrophic Conditions

Microalgae are promising candidates for sustainable wastewater treatment coupled to the production of biofuel, bioplastic and/or bio-fertilizers. In Nordic countries, however, light is a limiting factor for photosynthesis and biomass production during the winter season. Compared to municipal wastewater, industrial wastewater streams from the pulp and paper industry contain lower amounts of nitrogen, but high concentrations of carbon sources, which could be utilized by microalgae to enhance biomass production in limiting light. This study focused on the utilization of methanol, glycerol and xylose by five different Nordic microalgae [Chlorella vulgaris (13–1), Coelastrella sp. (3–4), Desmodesmus sp. (2–6), Chlorococcum sp. (MC1) and Scotiellopsis reticulata (UFA-2)] grown under mixotrophic conditions. Two of these strains, i.e., Chlorococcum sp. (MC1) and Scotiellopsis reticulata (UFA-2) were able to grow in the presence of xylose or methanol at concentrations of 6 g L–1, or 3%, respectively, in a 12/12 h day/night cycle. HPLC analysis confirmed the consumption of those substrates. Glycerol (2.3 g L–1) was tolerated by all strains and increased growth for Chlorella vulgaris (13–1), while higher concentrations (20 g L–1) were only tolerated by Chlorococcum sp. (MC-1). Fourier-transform infrared spectroscopy, performed after growth in presence of the dedicated carbon source, indicated an increase in the fingerprint region of the carbohydrate fraction. This was particularly the case for Chlorococcum sp. (MC1), when grown in presence of glycerol, and Scotiellopsis reticulata (UFA-2), when grown in presence of xylose. Therefore, these strains could be potential candidates for the production of biofuels, e.g., bioethanol or biogas. We could show that Nordic microalgae are able to grow on various carbon sources; the actual uptake rates are low during a 12/12 h day/night cycle requesting additional optimization of the cultivation conditions. Nonetheless, their potential to use pulp and paper waste-streams for cheap and sustainable biomass production is high and will support the development of new technologies, turning waste-streams into resources in a circular economy concept.

Fermentation redox potential control on the 1,3-propanediol production by Lactobacillus panis PM1

The fermentation redox potential was controlled during the production of 1,3-propanediol (PDO) by Lactobacillus panis PM1. Results show that the best redox potential level was at −200 mV at which had the highest PDO production (23.38 g/L) when compared to that controlled at -250 mV, −150 mV, and without control. For the redox potential level under investigation, the mass PDO yield with respect to glycerol was between 0.66 and 0.82. Potassium ferricyanide was chosen as an oxidant to control the redox potential level. With the addition of oxidant, the batch fermentation time was noticeably reduced compared to the one without the addition of oxidant. Furthermore, co-substrate utilization of glucose and glycerol was observed when potassium ferricyanide was present. It was postulated that such a co-substrate utilization pattern resulted from the redox imbalance where the activities of acetaldehyde dehydrogenase and alcohol dehydrogenase were retarded by the presence of potassium ferricyanide. To overcome the redox imbalance, the glycerol-reductive pathway was triggered to serve as the electron source to fuel the glycolysis pathway and PDO formation. The developed redox potential control strategy may benefit other specifically isolated PDO-producing strains and industrial PDO green processing to further enhance their productivity.

Recovery and utilization of crude glycerol, a biodiesel byproduct.

Biodiesel production has increased significantly in the past decade because it has been demonstrated to be a viable alternative and renewable fuel. Consequently, the production of crude glycerol, the main byproduct of the transesterification of lipids to biodiesel, has risen as well. Therefore, the effective recovery and utilization of crude glycerol can provide biodiesel with additional value. In this review, we first summarized the state-of-the-art progress on crude glycerol recovery and purification. Subsequently, numerous approaches have been reviewed for the utilization of crude glycerol, including use as animal feeds, for combustion, anaerobic fermentation, and chemical conversion. Finally, an extensive discussion and outlook is presented in relation to the techniques and processes in the chemical conversion of crude glycerol.

Characterization and Preparation of Ni/γAl2O3 Catalyst for Acetylation of Glycerol in a Fixed Bed Reactor Applied as an Octane Booster for Commercial Fuels

Glycerol is a by-product of biodiesel production with the amount of 10% of the total biodiesel product. To increase the utility and economic value of glycerol, it can be processed into several derivative products. One of the glycerol derivative products is currently being developed through the acetylation process. Glycerol acetylation product has been investigated as a component that can be used to increase the octane number of commercial fuels, otherwise known as bio-additives or octane boosters. This study aims to convert glycerol from the by-product of biodiesel production through the acetylation process using a modified solid catalyst Ni/γ-Al2O3 in a fixed bed reactor. The focus of this research is to study the effect of reactant flow rate and the mole ratio of glycerol to acetic acid on glycerol conversion. The variations used were flow rates of feed from 40, 60, 80 and 100 ml/minute, and the mole ratio of glycerol to acetic acid was 1:3, 1:5, 1:7, and 1:9. The experiment was carried out in several stages, namely: preparation and modification of the catalyst, the acetylation process and product application into commercial fuels. The acetylation reaction took place at a temperature of 100 °C and the mass of the catalyst used was 5% of the mass of glycerol. The results showed that the highest conversion of 74.24% was achieved under operating conditions with a reactant flow rate of 40 ml/min and glycerol to acetic acid mole ratio of 1:9. The utilization of acetylation products as bio-additives is carried out by adding reaction products to Pertamax fuel. The highest increase in octane number of Pertamax fuel at the addition of 8% volume of acetylation product from the initial octane number of 93 increased to 102 (increased by 10%).

Bioconversions of Biodiesel-Derived Glycerol into Sugar Alcohols by Newly Isolated Wild-Type Yarrowia lipolytica Strains

The utilization of crude glycerol, generated as a by-product from the biodiesel production process, for the production of high value-added products represents an opportunity to overcome the negative impact of low glycerol prices in the biodiesel industry. In this study, the biochemical behavior of Yarrowia lipolytica strains FMCC Y-74 and FMCC Y-75 was investigated using glycerol as a carbon source. Initially, the effect of pH value (3.0–7.0) was examined to produce polyols, intracellular lipids, and polysaccharides. At low pH values (initial pH 3.0–5.0), significant mannitol production was recorded. The highest mannitol production (19.64 g L−1) was obtained by Y. lipolytica FMCC Y-74 at pH = 3.0. At pH values ranging between 5.0 and 6.0, intracellular polysaccharides synthesis was favored, while polyols production was suppressed. Subsequently, the effect of crude glycerol and its concentration on polyols production was studied. Y. lipolytica FMCC Y-74 showed high tolerance to impurities of crude glycerol. Initial substrate concentrations influence polyols production and distribution with a metabolic shift toward erythritol production being observed when the initial glycerol concentration (Gly0) increased. The highest total polyols production (=56.64 g L−1) was obtained at Gly0 adjusted to ≈120 g L−1. The highest polyols conversion yield (0.59 g g−1) and productivity (4.36 g L−1 d−1) were reached at Gly0 = 80 g L−1. In fed-batch intermittent fermentation with glycerol concentration remaining ≤60 g L−1, the metabolism was shifted toward mannitol biosynthesis, which was the main polyol produced in significant quantities (=36.84 g L−1) with a corresponding conversion yield of 0.51 g g−1.

Potential utilization of glycerol as crosslinker in starch films for application in Regenerative Dentistry

Periodontal disease results in damage to dental insertion apparatus. Regenerative procedures are proposed to replace lost structures in the context of guided tissue regeneration (GTR), guided bone regeneration (GBR) techniques and frequently associate bone substitutes with physical barriers aiming at greater longevity and improvement of aesthetic pattern. This study evaluates the possibility of using glycerol as a starch films modifying agent, acting as a cross-linking agent, without compromising its plasticizing effect. Biodegradable cassava starch films were prepared incorporating glycerol at concentrations of 0, 15, 20, 30 and 40% aiming application at dental regenerative procedures. The characterization of films by microscopy (SEM), thermal analysis (DSC), spectroscopic (UV / Vis., FTIR, XRD), mechanical (Traction), and analysis of protein swelling, degradation and diffusion and physiological temperature) showed that the incorporation of glycerol in up to 20% attributed to the films a plasticizer character and in higher concentrations, conferred a greater interaction of glycerol (crosslinking) with the starch chains and a degradation time that allows the physical barrier in RTG and ROG. The films presented mechanical resistance, malleability and permissiveness to protein diffusion in the in vitro assays, which meet the current attributes that guide the use of these resources in biomaterials.