Malic acid production from biodiesel derived crude glycerol using morphologically controlled Aspergillus niger in batch fermentation

Bioleaching of rare earth elements from ores and waste materials: Current status, economic viability and future prospects

Rare earth elements (REEs) are critical components of numerous products widely used in many areas, and the demand for REEs is increasing dramatically in recent years. Physical-chemical leaching is commonly adopted for the recovery of REEs from ores and solid wastes, but concerns over the generation of hazards, operation safety, and environmental pollution have urged the transition to greener and more sustainable leaching methods. Bioleaching is considered an excellent alternative for the recovery of REEs. This review provided an overview on the REEs recovery from primary and secondary resources via different bioleaching strategies. The techno-economics of bioleaching for REEs recovery were highlighted, and key factors affecting the economic viability of bioleaching were identified. Finally, strategies including the utilization of low-cost substrates as feedstocks, non-sterile bioleaching, recycling and reutilization of biolixiviants, and development of robust bioleaching strains were proposed to improve the economic competitiveness of bioleaching. It is expected that this review could serve as a useful guideline on the design of more economically competitive bioleaching processes for the recovery REEs from different resources.

Large Flux Supply of NAD(H) under Aerobic Conditions by Candida glycerinogenes

NAD is a redox coenzyme and is the center of energy metabolism. In metabolic engineering modifications, an insufficient NAD(H) supply often limits the accumulation of target products. In this study, Candida glycerinogenes was found to be able to supply NAD(H) in large fluxes, up to 7.6 times more than Saccharomyces cerevisiae in aerobic fermentation. Aerobic fermentation in a medium without amino nitrogen sources demonstrated that C. glycerinogenes NAD synthesis was not dependent on NAD precursors in the medium. Inhibition by antisense RNA and the detection of transcript levels indicated that the main NAD supply pathway is the de novo biosynthesis pathway. It was further demonstrated that NAD(H) supply was unaffected by changes in metabolic flow through C. glycerinogenes ΔGPD aerobic fermentation (80 g/L ethanol). In conclusion, the ability of C. glycerinogenes to supply NAD(H) in large fluxes provides a new approach to solving the NAD(H) supply problem in synthetic biology.

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.

Metabolic engineering and fermentation optimization strategies for producing organic acids of the tricarboxylic acid cycle by microbial cell factories

The organic acids of the tricarboxylic acid (TCA) pathway are important platform compounds and are widely used in many areas. The high-productivity strains and high-efficient and low-cost fermentation are required to satisfy a huge market size. The high metabolic flux of the TCA pathway endows microorganisms potential to produce high titers of these organic acids. Coupled with metabolic engineering and fermentation optimization, the titer of the organic acids has been significantly improved in recent years. Herein, we discuss and compare the recent advances in synthetic pathway engineering, cofactor engineering, transporter engineering, and fermentation optimization strategies to maximize the biosynthesis of organic acids. Such engineering strategies were mainly based on the TCA pathway and glyoxylate pathway. Furthermore, organic-acid-secretion enhancement and renewable-substrate-based fermentation are often performed to assist the biosynthesis of organic acids. Further strategies are also discussed to construct high-productivity and acid-resistant strains for industrial large-scale production.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Optimization of Medium Constituents for the Production of Citric Acid from Waste Glycerol Using the Central Composite Rotatable Design of Experiments

Citric acid is currently produced by submerged fermentation of sucrose with the aid of Aspergillus niger mold. Its strains are characterized by a high yield of citric acid biosynthesis and no toxic by-products. Currently, new substrates are sought for production of citric acid by submerged fermentation. Waste materials such as glycerol or pomace could be used as carbon sources in the biosynthesis of citric acid. Due to the complexity of the metabolic state in fungus, there is an obvious need to optimize the important medium constituents to enhance the accumulation of desired product. Potential optimization approach is a statistical method, such as the central composite rotatable design (CCRD). The aim of this study was to increase the yield of citric acid biosynthesis by Aspergillus niger PD-66 in media with waste glycerol as the carbon source. A mathematical method was used to optimize the culture medium composition for the biosynthesis of citric acid. In order to maximize the efficiency of the biosynthesis of citric acid the central composite, rotatable design was used. Waste glycerol and ammonium nitrate were identified as significant variables which highly influenced the final concentration of citric acid (Y1), volumetric rate of citric acid biosynthesis (Y2), and yield of citric acid biosynthesis (Y3). These variables were subsequently optimized using a central composite rotatable design. Optimal values of input variables were determined using the method of the utility function. The highest utility value of 0.88 was obtained by the following optimal set of conditions: waste glycerol—114.14 g∙L−1and NH4NO3—2.85 g∙L−1.

Recent advances in producing food additive L-malate: Chassis, substrate, pathway, fermentation regulation and application

In addition to being an important intermediate in the TCA cycle, L-malate is also widely used in the chemical and beverage industries. Due to the resulting high demand, numerous studies investigated chemical methods to synthesize L-malate from petrochemical resources, but such approaches are hampered by complex downstream processing and environmental pollution. Accordingly, there is an urgent need to develop microbial methods for environmentally-friendly and economical L-malate biosynthesis. The rapid progress and understanding of DNA manipulation, cell physiology, and cell metabolism can improve industrial L-malate biosynthesis by applying intelligent biochemical strategies and advanced synthetic biology tools. In this paper, we mainly focused on biotechnological approaches for enhancing L-malate synthesis, encompassing the microbial chassis, substrate utilization, synthesis pathway, fermentation regulation, and industrial application. This review emphasizes the application of novel metabolic engineering strategies and synthetic biology tools combined with a deep understanding of microbial physiology to improve industrial L-malate biosynthesis in the future.

Development of In Situ Product Recovery (ISPR) System Using Amberlite IRA67 for Enhanced Biosynthesis of Hyaluronic Acid by Streptococcus zooepidemicus

High broth viscosity due to the accumulation of hyaluronic acid (HA) causes a limited yield of HA. It is a major problem of HA production using Streptococcus zooepidemicus. Extractive fermentation via in situ product recovery (ISPR) was utilized to enhance the HA production. Resins from Amberlite: IRA400 Cl; IRA900 Cl; IRA410 Cl; IRA402 Cl; and IRA67 were tested for the HA adsorption. IRA67 showed high adsorption capacity on HA. The study of the adsorption via a 2 L stirred tank bioreactor of S. zooepidemicus fermentation was investigated to elucidate the adsorption of HA onto IRA67 in dispersed and integrated internal column systems. The application of a dispersed IRA67 improved the HA production compared to the fermentation without resin addition by 1.37-fold. The HA production was further improved by 1.36-fold with an internal column (3.928 g/L) over that obtained with dispersed IRA67. The cultivation with an internal column shows the highest reduction of viscosity value after the addition of IRA67 resin: from 58.8 to 23.7 (mPa·s), suggesting the most effective ISPR of HA. The improved biosynthesis of HA indicated that an extractive fermentation by ISPR adsorption is effective and may streamline the HA purification.

Establishing a growth-coupled mechanism for high-yield production of β-arbutin from glycerol in Escherichia coli

Biodiesel production has increased significantly in recent years, leading to an increase in the production of crude glycerol. In this study, a novel growth-coupled erythrose 4-phosphate (E4P) formation strategy that can be used to produce high levels of β-arbutin using engineered Escherichia coli and glycerol as the carbon source was developed. In the strategy, E4P formation was coupled with cell growth, and a growth-driving force made the E4P formation efficient. By applying this strategy, efficient microbial synthesis of β-arbutin was achieved, with 7.91 g/L β-arbutin produced in shaking flask, and 28.1 g/L produced in a fed batch fermentation with a yield of 0.20 g/g glycerol and a productivity of 0.39 g/L/h. This is the highest β-arbutin production through microbial fermentation ever reported to date. This study may have significant implications in the large-scale production of β-arbutin as well as other aromatic compounds of importance.

Recent advances in microbial production of L-malic acid

Over the last few decades, increasing concerns regarding fossil fuel depletion and excessive CO2 emissions have led to extensive fundamental studies and industrial trials regarding microbial chemical production. As an additive or precursor, L-malic acid has been shown to exhibit distinctive properties in the food, pharmaceutical, and daily chemical industries. L-malic acid is currently mainly fabricated through a fumarate hydratase-based biocatalytic conversion route, wherein petroleum-derived fumaric acid serves as a substrate. In this review, for the first time, we comprehensively describe the methods of malic acid strain transformation, raw material utilization, malic acid separation, etc., especially recent progress and remaining challenges for industrial applications. First, we summarize the various pathways involved in L-malic acid biosynthesis using different microorganisms. We also discuss several strain engineering strategies for improving the titer, yield, and productivity of L-malic acid. We illustrate the currently available alternatives for reducing production costs and the existing strategies for optimizing the fermentation process. Finally, we summarize the present challenges and future perspectives regarding the development of microbial L-malic acid production. KEY POINTS: • A range of wild-type, mutant, laboratory-evolved, and metabolically engineered strains which could produce L-malic acid were comprehensively described. • Alternative raw materials for reducing production costs and the existing strategies for optimizing the fermentation were sufficiently summarized. • The present challenges and future perspectives regarding the development of microbial L-malic acid production were elaboratively discussed.

Optimization of l-malic acid production from acetate with Aspergillus oryzae DSM 1863 using a pH-coupled feeding strategy

Background

Malic acid, a dicarboxylic acid mainly used in the food industry, is currently produced from fossil resources. The utilization of low-cost substrates derived from biomass could render microbial processes economic. Such feedstocks, like lignocellulosic hydrolysates or condensates of fast pyrolysis, can contain high concentrations of acetic acid. Acetate is a suitable substrate for l-malic acid production with the filamentous fungus Aspergillus oryzae DSM 1863, but concentrations obtained so far are low. An advantage of this carbon source is that it can be used for pH control and simultaneous substrate supply in the form of acetic acid. In this study, we therefore aimed to enhance l-malate production from acetate with A. oryzae by applying a pH-coupled feeding strategy.

Results

In 2.5-L bioreactor fermentations, several feeding strategies were evaluated. Using a pH-coupled feed consisting of 10 M acetic acid, the malic acid concentration was increased about 5.3-fold compared to the batch process without pH control, resulting in a maximum titer of 29.53 ± 1.82 g/L after 264 h. However, it was not possible to keep both the pH and the substrate concentration constant during this fermentation. By using 10 M acetic acid set to a pH of 4.5, or with the repeated addition of NaOH, the substrate concentration could be maintained within a constant range, but these strategies did not prove beneficial as lower maximum titers and yields were obtained. Since cessation of malic acid production was observed in later fermentation stages despite carbon availability, a possible product inhibition was evaluated in shake flask cultivations. In these experiments, malate and succinate, which is a major by-product during malic acid production, were added at concentrations of up to 50 g/L, and it was found that A. oryzae is capable of organic acid production even at high product concentrations.

Conclusions

This study demonstrates that a suitable feeding strategy is necessary for efficient malic acid production from acetate. It illustrates the potential of acetate as carbon source for microbial production of the organic acid and provides useful insights which can serve as basis for further optimization.

Malic acid: fermentative production and applications

Microbial metabolites have gained lot of industrial interest. These are currently employed in various industries including pharmaceuticals, chemical, textiles, food etc. Organic acids are among the important microbial products. Production of microbial organic acids present numerous advantages like agro-industrial waste may be utilized as substrate, low production cost, natural in origin and production is environment friendly. Malic acid is an organic acid (C4 dicarboxylic acid) that can be produced by microbes. It is also useful in industrial sectors as food, chemicals, and pharmaceuticals etc. Production/extraction of malic acid has been reported from fruits, egg shells, microbes, via chemical synthesis, bio-transformation and from renewable sources. Microbial production of malic acid seems very promising due to various advantages and the approach is environment-friendly. In recent years, researchers have focused on fermentative microbial production of malic acid and possibility of using agro-industrial waste as raw substrates. In current article, malic acid production along with applications has been discussed with recent advances in the area.

Techno economic analysis of malic acid production using crude glycerol derived from waste cooking oil

In the present work, Aspergillus niger was employed to produce commercially valuable malic acid from crude glycerol derived from waste cooking oil. Crude glycerol dosage, yeast extract dosage and initial pH were the influencing factors playing a significant role in the malic acid synthesis. The optimal condition for malic acid biosynthesis was studied by using response surface methodology. Further the feasibility analysis for biosynthesis of malic acid from crude glycerol was studied using the laboratory scale optimized data, with this experimentally optimized data, plant was simulated using SuperPro Designer (v10). The cost involved for malic acid synthesis per unit volume was likely expected to be $0.43/kg of malic acid using reactive extraction method. Thus, process optimization combined with techno-economical analysis of malic acid production could be beneficial.

Recent advances in the development of Aspergillus for protein production

Aspergillus had been widely used in the industrial production of recombinant proteins. In addition to the safety and broad substrate utilization spectrum, its efficient post-translational modification and strong protein secretion capacity have significant advantages for developing an excellent protein-producing cell factory in industrial production. However, the difficulties in genetic manipulation of Aspergillus and varying expression levels of different heterologous proteins hampered its further development and application. Recently, the development of CRISPR genome editing and high-throughput screening platforms has facilitated the Aspergillus development of a wide range of modifications and applications. Meanwhile, multi-omics analysis and multiplexed genetic engineering have promoted effective knowledge mining. This paper provides a comprehensive and updated review of these advances, including high-throughput screening, genome editing, protein expression modules, and fermentation optimization. It also highlights and discusses the latest significant progress, aiming to provide a practical guide for implementing Aspergillus as an efficient protein-producing cell factory.

Immobilization of Aspergillus oryzae DSM 1863 for l-Malic Acid Production

Whole-cell immobilization by entrapment in natural polymers can be a tool for morphological control and facilitate biomass retention. In this study, the possibility of immobilizing the filamentous fungus Aspergillus oryzae for l-malic acid production was evaluated with the two carbon sources acetate and glucose. A. oryzae conidia were entrapped in alginate, agar, and κ-carrageenan and production was monitored in batch processes in shake flasks and 2.5-L bioreactors. With glucose, the malic acid concentration after 144 h of cultivation using immobilized particles was mostly similar to the control with free biomass. In acetate medium, production with immobilized conidia of A. oryzae in shake flasks was delayed and titers were generally lower compared to cultures with free mycelium. While all immobilization matrices were stable in glucose medium, disintegration of bead material and biomass detachment in acetate medium was observed in later stages of the fermentation. Still, immobilization proved advantageous in bioreactor cultivations with acetate and resulted in increased malic acid titers. This study is the first to evaluate immobilization of A. oryzae for malic acid production and describes the potential but also challenges regarding the application of different matrices in glucose and acetate media.

Transcriptome analysis of Rhizopus oryzae seed pellet formation using triethanolamine

Rhizopus oryzae (R. oryzae) can effectively produce organic acids, and its pellet formation in seed cultures has been shown to significantly enhance subsequent fermentation processes. Despite advances in strain development, simple and effective methods for inducing pellet morphology and a basic understanding of the mechanisms controlling this process could facilitate substantial increases in efficiency and product output. Here, we report that 1.5% triethanolamine (TEOA) in seed culture medium can activate the growth of R. oryzae spores in compact and uniform pellets which is optimal for fermentation conditions. Analysis of fermentation kinetics showed that the production of fumaric and L-malic acid increases 293% and 177%, respectively. Transcriptomic analysis revealed that exposure of R. oryzae to 1.5% TEOA during the seed culture activated the phosphatidylinositol and mitogen-activated protein kinase signaling pathways. Theses pathways subsequently stimulated the downstream carbohydrate-active synthases and hydrolases that required for cell wall component synthesis and reconstruction. Our results thus provide insight into the regulatory pathways controlling pellet morphology germane to the viability of seed cultures, and provide valuable reference data for subsequent optimization of organic acid fermentation by R. oryzae.

Microbial Biosynthesis of L-Malic Acid and Related Metabolic Engineering Strategies: Advances and Prospects

Malic acid, a four-carbon dicarboxylic acid, is widely used in the food, chemical and medical industries. As an intermediate of the TCA cycle, malic acid is one of the most promising building block chemicals that can be produced from renewable sources. To date, chemical synthesis or enzymatic conversion of petrochemical feedstocks are still the dominant mode for malic acid production. However, with increasing concerns surrounding environmental issues in recent years, microbial fermentation for the production of L-malic acid was extensively explored as an eco-friendly production process. The rapid development of genetic engineering has resulted in some promising strains suitable for large-scale bio-based production of malic acid. This review offers a comprehensive overview of the most recent developments, including a spectrum of wild-type, mutant, laboratory-evolved and metabolically engineered microorganisms for malic acid production. The technological progress in the fermentative production of malic acid is presented. Metabolic engineering strategies for malic acid production in various microorganisms are particularly reviewed. Biosynthetic pathways, transport of malic acid, elimination of byproducts and enhancement of metabolic fluxes are discussed and compared as strategies for improving malic acid production, thus providing insights into the current state of malic acid production, as well as further research directions for more efficient and economical microbial malic acid production.

Effects of fermentation treatments on Polygonatum odoratum flavones' antioxidant activities

The main aim of this study is to analyze antioxidant properties of Polygonatum odoratum fermented with bacteria, fungi and yeast. Antioxidant activities (1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging, hydroxyl radical scavenging, and anti-lipid peroxidation abilities) were assessed in samples of flavones isolated from fermented P. odoratum (Mill.) druce samples. Fermentations using Lactobacillus, yeast and Aspergillus were investigated. Results showed that the antioxidant ability of Polygonatum odoratum flavones was decreased by the fermentation of Lactobacillus and yeast. Aspergillus niger fermentation improved the antioxidant ability of P. odoratum flavones. In this study, effective antioxidant activity was achieved in flavones fermented with Aspergillus niger than yeast and Lactobacillus species.

Efficient repeated batch production of androstenedione using untreated cane molasses by Mycobacterium neoaurum driven by ATP futile cycle

The biotransformation of phytosterol to androstenedione (AD) by mycobacteria is a unique process accompanied by energy-producing. However, high intracellular ATP content can severely inhibit the efficient production of AD. In this study, a novel citrate-based ATP futile cycle (AFC) and pyruvate-based AFC were constructed for the first time. Application of AFCs reduced intracellular ATP and propionyl-CoA levels and increased NAD⁺/NADH ratios and cell viability. The forced consumption of ATP promotes the transcription of critical genes in propionyl-CoA metabolism. The synergistic effect of enhanced propionyl-CoA metabolism and AFC increased AD conversion yield from 60.6% to 97.3%. The AD productivity was further improved by repeated batch fermentation using untreated cane molasses. The maximum productivity was 181% higher than that of the original strain. Therefore, the strategy of combining AFC and repeated batch fermentation is a valuable tool for the efficient and low-cost production of AD and other steroidal pharmaceutical precursors.

Effect of utilization of crude glycerol as substrate on fatty acid composition of an oleaginous yeast Rhodotorula mucilagenosa IIPL32: Assessment of nutritional indices

This work studied the use of crude glycerol obtained from biodiesel industry as substrate to generate yeast lipid from Rhodotorula mucilagenosa IIPL32 MTCC 25056. Crude glycerol is a low value by product obtained from biodiesel industry. Rhodotorula mucilagenosa IIPL32 MTCC 25056 was evaluated for its potential to produce lipid using crude glycerol as sole source of carbon. Under nitrogen limiting condition a lipid and biomass content of 5.6 g/L and19.7 g/L were obtained from crude glycerol. The fatty acid profile was found to be interestingly rich in oleic acid (61.88%), linoleic acid (16.17%) and linolenic acid (1.03%) comprising ~80% of MUFA and PUFA of total lipid. Further, evaluations were attempted to compare MUFA rich yeast lipid against different plant-borne edible oils commonly used in India. In this study, nutritional indices were calculated to check feasibility of using yeast oil as a plausible blend to edible oil.

Enhanced malic acid production using Aspergillus niger coupled with in situ product recovery

In the present investigation, recovery of malic acid from the fermentation broth was performed by using in situ reactive extraction method employing different combination of amine and solvent systems. Totally six solvent mixtures were tested for toxicity on Aspergillus niger PJR1. Further, effect of solvent mixture concentration on separation of malic acid was investigated. Solvent system consisting of 2 M of trioctylamine in 1-octanol was found to be non-toxic to A. niger PJR1 and resulted in the maximum partition coefficient of 0.75 when the solvent mixture to liquid ratio of 1:2 used. A. niger PJR1 from crude glycerol using in situ reactive batch fermentation resulted in the maximum malic acid titer of 115.67 ± 3.5 g/L with the productivity of 0.53 g/L.h after 216 h. Further, fed batch extractive fermentation with crude glycerol resulted in malic acid titer of 131.48 ± 3.4 g/L with the productivity of 0.45 g/L.h after 288 h. Thus reactive extraction combined with in situ fermentation could become effective method for enhanced malic acid production.

Biochemical conversion of biodiesel by-product into malic acid: A way towards sustainability

Crude glycerol, one of the ever-growing by-product of biodiesel industry and is receiving the closest review in recent times because direct disposal of crude glycerol may emerge ecological issues. The renewability, bioavailability and typical structure of glycerol, therefore, discover conceivable application in serving the role of carbon and energy source for microbial biosynthesis of high value products. This conceivable arrangement could find exploitation of crude glycerol as a renewable building block for bio-refineries as it is economically as well as environmentally profitable. In this review, we summarize the uptake and catabolism of crude glycerol by different wild and recombinant microorganism. The chemical and biochemical transformation of crude glycerol into high esteem malic acid by various microbial pathways is also additionally discussed. An extensive investigation in the synthesis of high-value malic acid production from various feed stock which finds applications in cosmeceutical and chemical industries, food and beverages, and to some extent in the field of medical science is also likewise studied. Finally, the open doors for unrefined crude glycerol in serving as a promising abundant energy source for malic acid production in near future have been highlighted.

Enhancing methane yield from crude glycerol anaerobic digestion by coupling with ultrasound or A. niger/E. coli biodegradation

Anaerobic digestion of crude glycerol from biodiesel production is a feasible way for methane production. However, crude glycerol (CG) contains impurities, such as long-chain fatty acids (LCFA) that can inhibit methanogenic microorganisms. Ultrasound promotes the hydrolysis of LCFA and deagglomerates the microorganisms in biological flocs. Furthermore, Aspergillus niger and Escherichia coli produce lipases capable of degrading LCFA. This study aims at improving the methane yield from anaerobic digestion by coupling with ultrasound or E. coli/A. niger biodegradation. The effect of the different treatments was first assessed in a perfectly mixed batch reactor (PMBR), using diluted CG at concentrations of 0.2%, 1.7%, and 3.2% (v/v). Later, the best conditions were replicated in an upflow anaerobic sludge blanket (UASB) reactor to simulate full-scale practical applications. Experiments in the PMBR showed that ultrasound or A. niger biodegradation steps improved methane yield up to 11% for 0.2% CG and 99% for 1.7% CG, respectively. CG biodegradation by E. coli inhibited the subsequent anaerobic digestion for all concentrations tested. Using a UASB digester, ultrasonic treatment of CG led to an average increase of 29% in methane production. The application of ultrasound led to a lower accumulation of propionic acid in the digested material and increased biogas production. On the other hand, an average 77% increase in methane production was achieved using a preliminary CG biodegradation step by A. niger, when operated at a loading rate of 2.9 kg COD m^-3 day^-1. Under these conditions, an energy gain of 0.48 kWh day^-1, with the production of the 0.434 m³ CH₄ kg^-1 COD_removal and 0.573 m³ CH₄ kg^-1 VS, and a biogas quality of 73% in methane were obtained. The digested material was analyzed for the detection and quantification of added-value by-products in order to obtain a broad assessment of the CG valorization through anaerobic digestion. In some experiments, propionic and oxalic acid were detected. However, the accumulation of propionic caused the inhibition of the acetogenic and methanogenic microorganisms.

A review on variation in crude glycerol composition, bio-valorization of crude and purified glycerol as carbon source for lipid production

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.

Economical production of androstenedione and 9α-hydroxyandrostenedione using untreated cane molasses by recombinant mycobacteria

Production of androstenedione (AD) and 9α-hydroxyandrostenedione (9α-OH-AD) by recombinant mycobacteria using untreated cane molasses and hydrolysate of mycobacterial cells (HMC) was investigated for the first time. B-vitamins feeding experiment and reverse transcription-PCR analysis showed that propionyl-CoA carboxylase (PCC) plays an important role in the phytosterol biotransformation of mycobacteria. The respective AD and 9α-OH-AD conversion ratios were increased by 2.91 and 1.48 times through coexpression of PCC and NADH dehydrogenase. The highest conversion ratios of AD and 9α-OH-AD obtained by using a co-feeding strategy of cane molasses and HMC reached 96.38% and 95.04%, respectively, and the total costs of carbon and nitrogen sources for the culture medium were reduced by 29.89% and 49.49%, respectively. Taking the results together, untreated cane molasses and HMC can be used for the economical production of steroidal pharmaceutical precursors by mycobacteria. This study offers an economical and green strategy for steroidal pharmaceutical precursor production.

Improved itaconic acid production by Aspergillus niveus using blended algal biomass hydrolysate and glycerol as substrates

Superfluous algal biomass hydrolysate and purified glycerol obtained from biodiesel production were utilized for the production of itaconic acid by Aspergillus niveus. The lipid extracted Gracilaria edulis algal biomass residual was subjected to a pretreatment for the enhanced production of itaconic acid. Glycerol acquired from biodiesel production was pretreated and utilized as a substrate for itaconic acid production. The effect of individual and combined substrate concentration on itaconic acid production was investigated. Ultrasonication combined with the acid pretreated algal biomass produces higher itaconic acid due to the higher level of the total carbohydrate content (58.47 ± 2.57% w/v). After 168 h of incubation, A. niveus utilizes algal biomass hydrolysate and purified glycerol as substrate and produced 31.55 ± 1.25 g/L of itaconic acid and the dry cell weight is 18.24 ± 0.23 g/L respectively. Glycerol and algal biomass hydrolysate was a potential substrate for itaconic acid production by fungal species.

Process optimization and kinetic analysis of malic acid production from crude glycerol using Aspergillus niger

In the present work, optimization of crude glycerol fermentation to produce malic acid by using Aspergillus niger was investigated using response surface methodology and artificial neural network. Kinetic investigation of bioconversion of crude glycerol into malic acid using Aspergillus niger was studied using Monod, Mosser, and Haldane-Andrew models. Crude glycerol concentration, initial pH and yeast extract concentration were found to be significant compounds affecting malic acid production by Aspergillus niger. Both dry cell weight and malic acid titre were found decreased with increase in crude glycerol concentration. Haldane-Andrew model gave the best fit for the production of malic acid from crude glycerol with µ_max of 0.1542 h^-1. The maximum malic acid production obtained under optimum conditions was 92.64 + 1.54 g/L after 192 h from crude glycerol using Aspergillus niger.