Performance of Rhizopus, Rhizomucor, and Mucor in ethanol production from glucose, xylose, and wood hydrolyzates

Deeply analyzing dynamic fermentation of highland barley vinegar: Main physicochemical factors, key flavors, and dominate microorganisms

Highland barley vinegar, as a solid-state fermentation-type vinegar emerged recently, is well-known in Qinghai-Tibet plateau area of China. This work aimed to explore the main physicochemical factors, key flavor volatile compounds, and dominate microorganisms of highland barley vinegar during fermentation. The results showed that the decrease trend of reducing sugar, pH and the increase trend of amino acid nitrogen were associated with the metabolism of dominate bacteria, especially Lactobacillus and Acetobacter. Totally, 35 volatile compounds mainly including 20 esters, 10 alcohols, 2 aldehydes, 1 ketone and 2 pyrazines and 7 organic acids were identified. Especially, isoamyl acetate, acetyl methyl carbinol, ethyl caprylate, 1,2-propanediol, 3-methyl-1-butanol and ethyl isovalerate with high odor activity values were confirmed as key aroma compounds. Meanwhile, the relative average abundance of bacteria at genus level decreased significantly as fermentation time goes on. Among these microbes, Lactobacillus were the dominate bacteria at alcohol fermentation stage, Lactobacillus and Acetobacter were dominate at acetic acid fermentation stage. Furthermore, the correlations between dominate bacteria and the key volatile compounds were revealed, which highlighted Lactobacillus and Acetobacter were significantly correlated with key volatile compounds (|r| > 0.5, P < 0.01). The fundings of this study provide insights into the flavor and assist to improve the production quality of highland barley vinegar.

Genome-Scale Model of Rhizopus microsporus: Metabolic integration of a fungal holobiont with its bacterial and viral endosymbionts

Rhizopus microsporus often lives in association with bacterial and viral symbionts that alter its biology. This fungal model represents an example of the complex interactions established among diverse organisms in functional holobionts. We constructed a Genome-Scale Model (GSM) of the fungal-bacterial-viral holobiont (iHol). We employed a constraint-based method to calculate the metabolic fluxes to decipher the metabolic interactions of the symbionts with their host. Our computational analyses of iHol simulate the holobiont's growth and the production of the toxin rhizoxin. Analyses of the calculated fluxes between R. microsporus in symbiotic (iHol) versus asymbiotic conditions suggest that changes in the lipid and nucleotide metabolism of the host are necessary for the functionality of the holobiont. Glycerol plays a pivotal role in the fungal-bacterial metabolic interaction, as its production does not compromise fungal growth, and Mycetohabitans bacteria can efficiently consume it. Narnavirus RmNV-20S and RmNV-23S affected the nucleotide metabolism without impacting the fungal-bacterial symbiosis. Our analyses highlighted the metabolic stability of Mycetohabitans throughout its co-evolution with the fungal host. We also predicted changes in reactions of the bacterial metabolism required for the active production of rhizoxin. This iHol is the first GSM of a fungal holobiont.

Effect of Koji on Flavor Compounds and Sensory Characteristics of Rice Shochu

Koji is an important starter for rice shochu brewing and influences the rice shochu quality. Consequently, we studied the impacts of koji on the flavor compounds and sensory characteristics of rice shochu using molds Aspergillus kawachii SICC 3.917 (A-K), Aspergillus oryzae SICC 3.79(A-O), Aspergillus Niger CICC 2372 (A-N), Rhizopus oryzae CICC 40260 (R-O), and the traditional starter Qu (control). The effects of koji on the aroma components, free amino acids (FAAs), and overall sensory aspects of rice shochu were studied. These findings indicated that koji significantly affected the rice shochu’s quality. The content of total FAAs in rice shochu A-K (30.586 ± 0.944 mg/L) and A-O (29.919 ± 0.278 mg/L) was higher than others. The content of flavor compounds revealed that the aroma of rice shochu with various koji varied greatly from the smells of alcohols and esters. Shochu A-O had a higher concentration of aroma compounds and it exhibited a strong aroma and harmonious taste compared with the others. This research using taste compounds, FAAs, flavor intensity, and partial least squares regression (PLSR) showed that shochu A-O appeared to possess the best sensory qualities, with elevated concentrations of alcohols and sweet FAAs and lesser concentrations of sour FAAs. Therefore, the A-O mold is promising for the manufacture of rice shochu with excellent flavor and sensory characteristics.

Screening of Fusarium moniliforme as Potential Fungus for Integrated Biodelignification and Consolidated Bioprocessing of Napier Grass for Bioethanol Production

A fungus capable of producing ethanol from various carbon substrates was screened for direct ethanol production from lignocellulose. Fusarium moniliforme BIOTECH 3170 produced ethanol from glucose, xylose, and cellobiose after three days with theoretical yields of 86.4%, 68.6%, and 45.4%, respectively. The coculture of glucose and xylose progressed sequentially at 79.2% of the theoretical yield, with both sugars completely consumed in five days. The solid-state consolidated bioprocessing of cellulose produced 25.2 g/L of ethanol after 20 days. After 28 days of the integrated biodelignification and consolidated bioprocessing of Napier grass at solid-state conditions, up to 10.5 g/L of ethanol was produced, corresponding to an ethanol yield of 0.032 g/g biomass. Given a sufficient carbon source, the screened fungus could produce up to 42.06 g/L ethanol. F. moniliforme BIOTECH 3170 demonstrated the characteristics of a fungus for potential ethanol production from cellulose, mixed sugars, and lignocellulosic materials.

Inhibitory and Stimulatory Effects of Fruit Bioactive Compounds on Edible Filamentous Fungi: Potential for Innovative Food Applications

The fermentation of fruit processing residuals (FPRs) with filamentous fungi can provide protein-rich food products. However, FPRs that contain bioactive compounds with antimicrobial properties present a major challenge. In this work, the resistance of two edible filamentous fungi, Rhizopus oligosporus and Neurospora intermedia, to 10 typically inhibiting bioactive compounds available in FPRs (epicatechin, quercetin, ellagic acid, betanin, octanol, hexanal, D-limonene, myrcene, car-3-ene, and ascorbic acid) was examined. These compounds’ inhibitory and stimulatory effects on fungal growth were examined individually. Three different concentrations (2.4, 24, and 240 mg/L) within the natural concentration range of these compounds in FPRs were tested. These bioactive compounds stimulated the growth yield and glucose consumption rate of R. oligosporus, while there was no increase in the biomass yield of N. intermedia. Ellagic acid caused an up to four-fold increase in the biomass yield of R. oligosporus. In addition, octanol and D-limonene showed antifungal effects against N. intermedia. These results may be helpful in the development of fungus-based novel fermented foods.

The role of filamentous fungi in advancing the development of a sustainable circular bioeconomy

Human activities generate enormous amounts of organic wastes and residues. Filamentous fungi (FF) are able to grow on a broad range of substrates and survive over a wide spectrum of growth conditions. These characteristics enable FF to be exploited in biorefineries for various waste streams. Valorization of food industry byproducts into biomass and various arrays of value-added products using FF creates promising pathways toward a sustainable circular economy. This approach might also contribute to reaching the sustainable development goals set by the United Nations, particularly for zero hunger as well as affordable and clean energy. This paper presents the application of filamentous fungi in food, feeds, fuels, biochemicals, and biopolymers. The nutritional values, health benefits, and safety of foods derived from byproducts of food industries are also addressed. The technoeconomical feasibilities, sustainability aspects and challenges and future perspectives for biorefineries using filamentous fungi are discussed.

Effect of Zinc-Calcium on Xylose Consumption by Mucor circinelloides (MN128960): Xylitol and Ethanol Yield Optimization

Xylose is the second most abundant monomeric sugar on earth. Nevertheless, metabolizing xylose into ethanol is a complex process due to several biochemical reactions. Some microorganisms of the genus Mucor are suitable for this bioprocess. Using metal ions, such as zinc and calcium, allows some fungal species to increase their ethanol yield. In this work, the wild strain Mucor spp. (C1502) was molecularly identified via internal transcribed spacer (ITS) sequencing. Secondly, an optimization using response surface methodology (RSM) with a central composite experimental design (CCD) was carried out. The independent variables (X) were ZnSO4·7H2O (X1, 0.0–1.5 g/L) and CaCl2 (X2, 0.0–2.5 g/L) concentration in the fermentation broth in order to demonstrate the effect of these ions, xylose was used as the only carbon source. The dependent variables (Y) measured were ethanol yield (Y1, g ethanol/g xylose) and xylitol yield (Y2, g xylitol/g xylose). The identified strain, Mucor circinelloides, was given the accession number MN128960 by the NCBI. Once the optimal concentrations of zinc and calcium were calculated, experimental validation was performed, with the highest ethanol and xylitol yields reaching 0.36 g ethanol/g xylose and 0.35 g xylitol/g xylose, respectively. This study demonstrated that increasing the xylitol yield using the effect of the ions, zinc and calcium, increases the ethanol yield. Furthermore, M. circinelloides (C1502) can produce metabolites, such as ethanol and xylitol, from the xylose obtained from hemicellulose biomasses, which can be used as a carbon source at low cost and with great availability.

Exploring Simplified Methods for Insect Chitin Extraction and Application as a Potential Alternative Bioethanol Resource

Simple Summary

The studies on chitin utilization as a source for bioethanol production are still very few. The present study explores some simple methods for insect chitin extraction and application in bioethanol production. Using insect chitin in bioethanol production, may help decreasing the dependence on energy crops as a carbon source for bioethanol. Fungal strains of Mucor circinelloides were reported previously to bio-convert chitin directly to ethanol in submerged fermentation systems. In our study, we explored the bioconversion of insect chitin to bioethanol using two different strains of Mucor circinelloides in submerged fermentation systems. An insect-isolated M. circinelloides strain was found to bio-convert the extracted chitin directly to ethanol in submerged fermentation system. The source of strain isolation and the pH of the production medium were showed to influence the chitin bioconversion directly to bioethanol. All fermentation processes can be conducted easily, using the whole growing microorganism instead of using purified enzymes. These results highlight the insect biomass as a potential new, cheap and renewable source for bioethanol production simply, using a potent insect-isolated M. circinelloides strain.

Abstract

Chitin, the second most plentiful biopolymer in nature, is a major component of insect cuticle. In searching for alternative resources for fossil fuels, some fungal strains of Mucor circinelloides from an insect-source were found to produce bioethanol directly using insect chitin as a substrate. Herein, simplified methods for insect chitin extraction and application as a substrate in submerged fermentation for bioethanol production were explored. Chitin of the American cockroach (Periplaneta americana (L.)) was isolated by refluxing the cockroaches dried exoskeletons with 4% NaOH. The purity of the extracted chitin was assessed to be high when the physicochemical properties of the extracted chitin matched these of commercially available crab and shrimp samples. The extracted chitin was employed as a substrate in submerged fermentation using two strains of M. circinelloides. One of these, strains M. circinelloides 6017 showed immense potential for bioethanol production directly. It could to bio-transform 15 g/L of colloidal chitin directly to 11.22 ± 0.312 g/L of bioethanol (74% of the initial chitin mass) after 6 days of incubation. These results confirm the possibility of using insect biomass as a potential alternative resource for bioethanol production in a simple manner thus contributing to the creation of an alternate energy source.

Process Strategies for the Transition of 1G to Advanced Bioethanol Production

Nowadays, the transport sector is one of the main sources of greenhouse gas (GHG) emissions and air pollution in cities. The use of renewable energies is therefore imperative to improve the environmental sustainability of this sector. In this regard, biofuels play an important role as they can be blended directly with fossil fuels and used in traditional vehicles’ engines. Bioethanol is the most used biofuel worldwide and can replace gasoline or form different gasoline-ethanol blends. Additionally, it is an important building block to obtain different high added-value compounds (e.g., acetaldehyde, ethylene, 1,3-butadiene, ethyl acetate). Today, bioethanol is mainly produced from food crops (first-generation (1G) biofuels), and a transition to the production of the so-called advanced ethanol (obtained from lignocellulosic feedstocks, non-food crops, or industrial waste and residue streams) is needed to meet sustainability criteria and to have a better GHG balance. This work gives an overview of the current production, use, and regulation rules of bioethanol as a fuel, as well as the advanced processes and the co-products that can be produced together with bioethanol in a biorefinery context. Special attention is given to the opportunities for making a sustainable transition from bioethanol 1G to advanced bioethanol.

Fermentation Dynamics and Benzylic Derivative Production in Ischnoderma resinosum Isolates

Fermentation dynamics and benzylic derivative production were evaluated in the fermentation broth of six different Ischnoderma resinosum (P. Karst) isolates over a period of 30 days to understand their potential applications in bioreactor optimization for natural flavor compound production. d-Glucose and d-fructose levels decreased from 20.4 ± 0.4 to 7.1 ± 1.4 g/L and 1.0 ± 0.1 to <0.1 g/L, respectively, in all fermentations. Isolate I₂ produced the highest concentration of ethanol (546. 4 ± 0.4 mg/L). l-Lactic acid production varied between 4.3 ± 0.6 and 3.7 ± 0.2 mg/L, whereas acetic acid concentrations decreased from 81.0 ± 3.3 to <40.0 mg/L. pH decreased from 4.9 ± 0.0 to 3.6 ± 0.4 at the end of 30 days in all fermentations. Isolate I₃ was the highest producer of benzaldehyde (BA) (12.0 ± 0.2 mg/kg) and 4-methoxybenzaldehyde (4-MBA) (239.6 ± 3.9 mg/kg), while isolate I₄ was the highest producer of 3,4-dimethoxybenzaldehyde (3,4-DMBA) (27.8 ± 0.2 mg/18 kg). Identification of isolate I₃ as a high BA and 4-MBA producer and isolate I₄ as a high 3,4-DMBA producer suggested differential benzylic derivative production among I. resinosum isolates. This study lays the foundation for future investigations evaluating additional I. resinosum isolates for benzylic derivative production as well as studies aimed at bioreactor optimization with potential commercial application.

Utilization of food waste-derived volatile fatty acids for production of edible Rhizopus oligosporus fungal biomass

Rhizopus oligosporus is an edible filamentous fungus that can contribute to meet the growing demand for single-cell protein. Volatile fatty acids (VFAs) are favorable potential substrates for producing R. oligosporus biomass due to their capacity to be synthesized from a wide range of low-value organic solid wastes via anaerobic digestion. The goal of this work was to cultivate R. oligosporus using food waste-derived VFAs as the sole carbon source. To maintain the requisite low substrate concentrations, the fed-batch cultivation technique was applied. This resulted in a four-fold improvement in biomass production relative to standard batch cultivation. Maximum biomass yield of 0.21 ± 0.01 g dry biomass/g VFAs _{COD eq. consumed}, containing 39.28 ± 1.54% crude protein, was obtained. In the bubble-column bioreactors, the complete uptake of acetic acid was observed, while the consumptions of caproic and butyric acids reached up to 97.64% and 26.13%, respectively.

Conservation of Xylose Fermentability in Phlebia Species and Direct Fermentation of Xylan by Selected Fungi

In efforts to lower the cost of total conversion of lignocellulosic materials, utilization of hemicellulose must be considered. White-rot fungus Phlebia sp. MG-60 can produce ethanol directly from cellulose and has fermentation ability for glucose, cellulose, and xylose. Therefore, white-rot fungi can be considered a good candidate for consolidated bioprocessing to give bioethanol from lignocellulosic biomass, although little information is available on the direct fermentation of xylan. In the present study, some Phlebia species were selected as candidates because of their ability to ferment xylose to ethanol more efficiently than Phlebia sp. MG-60. This process indicated that the basidiomycetes that can produce ethanol from xylose are closely related genetically within the Phlebia genus. The selected Phlebia species showed higher ethanol productivity from corn core and beechwood xylans than Phlebia sp. MG-60. The ethanol yields from corn core xylan in culture with Phlebia acerina HHB11146, Phlebia ludoviciana HHB9640, and Phlebia subochracea HHB8494 were 46.2%, 46.7%, and 39.7% of theoretical maximum, and those from beechwood xylan were 19.09%, 17.7%, and 21.4% of the theoretical maximum, respectively.

Mucor indicus and Rhizopus oryzae co-culture to improve the flavor of Chinese turbid rice wine

BACKGROUND

One of the most important species used to ferment Chinese turbid rice wine (CTRW) at an industrial-scale level is Rhizopus oryzae, although the flavor of CTRW fermented by pure R. oryzae is inferior to that of traditional CTRW.

RESULTS

Mucor indicus was used as a cooperative species to improve the flavor of CTRW presented by R. oryzae. The flavor compounds in different fermentation stages were determined by headspace solid-phase microextraction-gas chromatography-mass spectrometry and high-performance liquid chromatography. It was noted that the M. indicus and R. oryzae co-culture changed the profiles of flavor compounds in CTRW, including esters, higher alcohols, amino acids and organic acids, and also significantly enhanced the concentration of sweet amino acids, fruity and floral esters, and higher alcohols. Sensory evaluation demonstrated that the CTRW fermented by M. indicus and R. oryzae had a more intense aroma, harmonious taste, continuation and full body mouth-feel because of more abundant flavor compounds.

CONCLUSION

Mucor indicus is a promising species for co-culture with R. oryzae to improve the flavor of CTRW. © 2019 Society of Chemical Industry.

A quantitative image analysis pipeline for the characterization of filamentous fungal morphologies as a tool to uncover targets for morphology engineering: a case study using aplD in Aspergillus niger

BACKGROUND

Fungal fermentation is used to produce a diverse repertoire of enzymes, chemicals, and drugs for various industries. During submerged cultivation, filamentous fungi form a range of macromorphologies, including dispersed mycelia, clumped aggregates, or pellets, which have critical implications for rheological aspects during fermentation, gas/nutrient transfer, and, thus, product titres. An important component of strain engineering efforts is the ability to quantitatively assess fungal growth phenotypes, which will drive novel leads for morphologically optimized production strains.

RESULTS

In this study, we developed an automated image analysis pipeline to quantify the morphology of pelleted and dispersed growth (MPD) which rapidly and reproducibly measures dispersed and pelleted macromorphologies from any submerged fungal culture. It (i) enables capture and analysis of several hundred images per user/day, (ii) is designed to quantitatively assess heterogeneous cultures consisting of dispersed and pelleted forms, (iii) gives a quantitative measurement of culture heterogeneity, (iv) automatically generates key Euclidian parameters for individual fungal structures including particle diameter, aspect ratio, area, and solidity, which are also assembled into a previously described dimensionless morphology number MN, (v) has an in-built quality control check which enables end-users to easily confirm the accuracy of the automated calls, and (vi) is easily adaptable to user-specified magnifications and macromorphological definitions. To concomitantly provide proof of principle for the utility of this image analysis pipeline, and provide new leads for morphologically optimized fungal strains, we generated a morphological mutant in the cell factory Aspergillus niger based on CRISPR-Cas technology. First, we interrogated a previously published co-expression networks for A. niger to identify a putative gamma-adaptin encoding gene (aplD) that was predicted to play a role in endosome cargo trafficking. Gene editing was used to generate a conditional aplD expression mutant under control of the titratable Tet-on system. Reduced aplD expression caused a hyperbranched growth phenotype and diverse defects in pellet formation with a putative increase in protein secretion. This possible protein hypersecretion phenotype could be correlated with increased dispersed mycelia, and both decreased pellet diameter and MN.

CONCLUSION

The MPD image analysis pipeline is a simple, rapid, and flexible approach to quantify diverse fungal morphologies. As an exemplar, we have demonstrated that the putative endosomal transport gene aplD plays a crucial role in A. niger filamentous growth and pellet formation during submerged culture. This suggests that endocytic components are underexplored targets for engineering fungal cell factories.

Microbial conversion of xylose into useful bioproducts

Microorganisms can produce a number of different bioproducts from the sugars in plant biomass. One challenge is devising processes that utilize all of the sugars in lignocellulosic hydrolysates. D-xylose is the second most abundant sugar in these hydrolysates. The microbial conversion of D-xylose to ethanol has been studied extensively; only recently, however, has conversion to bioproducts other than ethanol been explored. Moreover, in the case of yeast, D-xylose may provide a better feedstock for the production of bioproducts other than ethanol, because the relevant pathways are not subject to glucose-dependent repression. In this review, we discuss how different microorganisms are being used to produce novel bioproducts from D-xylose. We also discuss how D-xylose could be potentially used instead of glucose for the production of value-added bioproducts.

Lignocellulose integration to 1G-ethanol process using filamentous fungi: fermentation prospects of edible strain of Neurospora intermedia

Background

Integration of first- and second-generation ethanol processes is one among the alternate approaches that efficiently address the current socio-economic issues of the bioethanol sector. Edible filamentous fungus capable of utilizing pentoses from lignocelluloses and also possessing biomass application as potential animal feed component was used as the fermentation strain for the integration model. This study presents various fermentation aspects of using edible filamentous fungi in the integrated first and second generation ethanol process model.

Results

Fermentation of edible strain of N. intermedia on the integrated first and second-generation ethanol substrate (the mixture of dilute acid pretreated and enzymatically hydrolyzed wheat straw and thin stillage from the first-generation ethanol process), showed an ethanol yield maximum of 0.23 ± 0.05 g/g dry substrate. The growth of fungal pellets in presence of fermentation inhibitors (such as acetic acid, HMF and furfural) resulted in about 11 to 45% increase in ethanol production as compared to filamentous forms, at similar growth conditions in the liquid straw hydrolysate. Fungal cultivations in the airlift reactor showed strong correlation with media viscosity, reaching a maximum of 209.8 ± 3.7 cP and resulting in 18.2 ± 1.3 g/L biomass during the growth phase of fungal pellets.

Conclusion

N. intermedia fermentation showed high sensitivity to the dilute acid lignocellulose pretreatment process, with improved fermentation performance at milder acidic concentrations. The rheological examinations showed media viscosity to be the most critical factor influencing the oxygen transfer rate during the N. intermedia fermentation process. Mycelial pellet morphology showed better fermentation efficiency and high tolerance towards fermentation inhibitors.

Comparative Genomic Insights into Endofungal Lifestyles of Two Bacterial Endosymbionts, Mycoavidus cysteinexigens and Burkholderia rhizoxinica

Endohyphal bacteria (EHB), dwelling within fungal hyphae, markedly affect the growth and metabolic potential of their hosts. To date, two EHB belonging to the family Burkholderiaceae have been isolated and characterized as new taxa, Burkholderia rhizoxinica (HKI 454^T) and Mycoavidus cysteinexigens (B1-EB^T), in Japan. Metagenome sequencing was recently reported for Mortierella elongata AG77 together with its endosymbiont M. cysteinexigens (Mc-AG77) from a soil/litter sample in the USA. In the present study, we elucidated the complete genome sequence of B1-EB^T and compared it with those of Mc-AG77 and HKI 454^T. The genomes of B1-EB^T and Mc-AG77 contained a higher level of prophage sequences and were markedly smaller than that of HKI 454^T. Although the B1-EB^T and Mc-AG77 genomes lacked the chitinolytic enzyme genes responsible for invasion into fungal cells, they contained several predicted toxin-antitoxin systems including an insecticidal toxin complex and PIN domain imposing an addiction-like mechanism essential for endohyphal growth control during host colonization. Despite the different host fungi, the alignment of amino acid sequences showed that the HKI 454^T genome consisted of 1,265 (32.6%) and 1,221 (31.5%) orthologous coding sequences (CDSs) with those of B1-EB^T and Mc-AG77, respectively. This comparative study of three phylogenetically associated endosymbionts has provided insights into their origin and evolution, and suggests the later bacterial invasion and adaptation of B1-EB^T to its host metabolism.

Optimization of fermentation conditions for efficient ethanol production by Mucor hiemalis

Background

Mucor hiemalis is a dimorphic fungus that efficiently produces ethanol from different sugars; however, the yield of ethanol production highly depends on the fermentation conditions.

Objective

The conditions for obtaining a high ethanol production yield were optimized in this study.

Materials and methods

A response surface methodology was used to optimize pH, temperature, and time of ethanolic fermentation by M. hiemalis. Additionally, wheat flour was enzymatically hydrolyzed and the hydrolysate solution with high glucose concentration was fermented by the fungus.

Results

The optimum pH, temperature, and time were 5.5, 30°C, and 36 h, respectively. Maximum ethanol and glycerol yields were 0.48 and 0.06 g/g, respectively. The biomass yield was between 0.01 and 0.16 g/g of consumed glucose. The results showed that the fungus was able to produce ethanol in a medium containing 5.5% (v/v) ethanol, while higher ethanol concentration prevented further production of ethanol.

Conclusion

At the optimized conditions, the fungus was able to consume glucose with the concentration of 140 g/L and produce ethanol with a yield of 0.45 g/g, which was comparable to that by Saccharomyces cerevisiae.

Sustainable carbon sources for microbial organic acid production with filamentous fungi

BACKGROUND

The organic acid producer Aspergillus oryzae and Rhizopus delemar are able to convert several alternative carbon sources to malic and fumaric acid. Thus, carbohydrate hydrolysates from lignocellulose separation are likely suitable as substrate for organic acid production with these fungi.

RESULTS

Before lignocellulose hydrolysate fractions were tested as substrates, experiments with several mono- and disaccharides, possibly present in pretreated biomass, were conducted for their suitability for malic acid production with A. oryzae. This includes levoglucosan, glucose, galactose, mannose, arabinose, xylose, ribose, and cellobiose as well as cheap and easy available sugars, e.g., fructose and maltose. A. oryzae is able to convert every sugar investigated to malate, albeit with different yields. Based on the promising results from the pure sugar conversion experiments, fractions of the organosolv process from beechwood (Fagus sylvatica) and Miscanthus giganteus were further analyzed as carbon source for cultivation and fermentation with A. oryzae for malic acid and R. delemar for fumaric acid production. The highest malic acid concentration of 37.9 ± 2.6 g/L could be reached using beechwood cellulose fraction as carbon source in bioreactor fermentation with A. oryzae and 16.2 ± 0.2 g/L fumaric acid with R. delemar.

CONCLUSIONS

We showed in this study that the range of convertible sugars for A. oryzae is even higher than known before. We approved the suitability of fiber/cellulose hydrolysate obtained from the organosolv process as carbon source for A. oryzae in shake flasks as well as in a small-scale bioreactor. The more challenging hemicellulose fraction of F. sylvatica was also positively evaluated for malic acid production with A. oryzae.

Rhizopus oryzae - Ancient microbial resource with importance in modern food industry

Filamentous fungi are microorganisms widely known for their diverse biochemical features. Fungi can efficiently invade a wide variety of substrates under operational conditions producing numerous bioproducts of interest, such as enzymes, organic acids, aromatic compounds and colorants. An additional interesting characteristic of some fungi is their safety classification for different uses, which guarantees that the bioproducts obtained from them do not contain any toxic component deleterious to humans. Rhizopus oryzae is among this group of fungi and is classified as a GRAS filamentous fungus, commonly used for production of some oriental traditional foods. It is mainly recognized as a good producer of lactic acid; however, its potential for other biotechnological processes is under study. This review analyzes and discusses the current scientific and technical contributions which may maximize the potential of R. oryzae as a producer of different compounds of industrial interest.

Characterization and gene cloning of l-xylulose reductase involved in l-arabinose catabolism from the pentose-fermenting fungus Rhizomucor pusillus

l-Xylulose reductase (LXR) catalyzes the reduction of l-xylulose to xylitol in the fungal l-arabinose catabolic pathway. LXR (RpLXR) was purified from the pentose-fermenting zygomycetous fungus Rhizomucor pusillus NBRC 4578. The native RpLXR is a homotetramer composed of 29 kDa subunits and preferred NADPH as a coenzyme. The K_m values were 8.71 mM for l-xylulose and 3.89 mM for dihydroxyacetone. The lxr3 (Rplxr3) gene encoding RpLXR consists of 792 bp and encodes a putative 263 amino acid protein (M_r = 28,341). The amino acid sequence of RpLXR showed high similarity to 3-oxoacyl-(acyl-carrier-protein) reductase. The Rplxr3 gene was expressed in Escherichia coli and the recombinant RpLXR exhibited properties similar to those of native RpLXR. Transcription of the Rplxr3 gene in R. pusillus NBRC 4578 was induced in the presence of l-arabinose and inhibited in the presence of d-glucose, d-xylose, and d-mannitol, indicating that RpLXR is involved in the l-arabinose catabolic pathway.

Retraction: Characterization of cellulolytic activities of newly isolated Thelephora sowerbyi from North-Western Himalayas on different lignocellulosic substrates

Characterization of cellulolytic activities of newly isolated Thelephora sowerbyi from North-Western Himalayas on different lignocellulosic substrate J. Basic Microbiol. 2015, 55, 1-11 - DOI: 10.1002/jobm.201500107 The above article from the Journal of Basic Microbiology, published online on 08 June 2015 in Wiley Online Library as Early View (http://onlinelibrary.wiley.com/doi/10.1002/jobm.201500107/pdf), has been retracted by agreement between the authors, the Editor-in-Chief and Wiley-VCH GmbH & Co. KGaA. The retraction has been agreed because the microorganism studied in the described experiments has been identified as the fungus Cotylidia pannosa (Gene Accession No. KT008117) instead of Thelephora sowerbyi. The culture has been identified on the basis of the sequence of the amplified ITS region of the microorganism which was submitted by the authors to the NCBI database.

Metabolic Engineering of Fusarium oxysporum to Improve Its Ethanol-Producing Capability

Fusarium oxysporum is one of the few filamentous fungi capable of fermenting ethanol directly from plant cell wall biomass. It has the enzymatic toolbox necessary to break down biomass to its monosaccharides and, under anaerobic and microaerobic conditions, ferments them to ethanol. Although these traits could enable its use in consolidated processes and thus bypass some of the bottlenecks encountered in ethanol production from lignocellulosic material when Saccharomyces cerevisiae is used—namely its inability to degrade lignocellulose and to consume pentoses—two major disadvantages of F. oxysporum compared to the yeast—its low growth rate and low ethanol productivity—hinder the further development of this process. We had previously identified phosphoglucomutase and transaldolase, two major enzymes of glucose catabolism and the pentose phosphate pathway, as possible bottlenecks in the metabolism of the fungus and we had reported the effect of their constitutive production on the growth characteristics of the fungus. In this study, we investigated the effect of their constitutive production on ethanol productivity under anaerobic conditions. We report an increase in ethanol yield and a concomitant decrease in acetic acid production. Metabolomics analysis revealed that the genetic modifications applied did not simply accelerate the metabolic rate of the microorganism; they also affected the relative concentrations of the various metabolites suggesting an increased channeling toward the chorismate pathway, an activation of the γ-aminobutyric acid shunt, and an excess in NADPH regeneration.

Fungal-mediated consolidated bioprocessing: the potential of Fusarium oxysporum for the lignocellulosic ethanol industry

Microbial bioprocessing of lignocellulose to bioethanol still poses challenges in terms of substrate catabolism. The most important challenge is to overcome substrate recalcitrance and to thus reduce the number of steps needed to biorefine lignocellulose. Conventionally, conversion involves chemical pretreatment of lignocellulose, followed by hydrolysis of biomass to monomer sugars that are subsequently fermented into bioethanol. Consolidated bioprocessing (CBP) has been suggested as an efficient and economical method of manufacturing bioethanol from lignocellulose. CBP integrates the hydrolysis and fermentation steps into a single process, thereby significantly reducing the amount of steps in the biorefining process. Filamentous fungi are remarkable organisms that are naturally specialised in deconstructing plant biomass and thus they have tremendous potential as components of CBP. The fungus Fusarium oxysporum has potential for CBP of lignocellulose to bioethanol. Here we discuss the complexity and potential of CBP, the bottlenecks in the process, and the potential influence of fungal genetic diversity, substrate complexity and new technologies on the efficacy of CPB of lignocellulose, with a focus on F. oxysporum.

Optimization of glucoamylase production by Mucor indicus, Mucor hiemalis, and Rhizopus oryzae through solid state fermentation / Mucor indicus, Mucor hiemalis, ve Rhizopus oryzae tarafından üretien glukoamilazın katı hal fermantasyonu ile optimizasyonu

Objective: Glucoamylase is a hydrolyzing enzyme with several industrial applications. Glucoamylase was produced via a solid state fermentation by three naturally occurring zygomycetes fungi of Mucor indicus, Mucor hiemalis, and Rhizopus oryzae on wheat bran.

Methods: The effects of cultivation temperature, medium moisture content, and cultivation time on the enzyme production were investigated. Experiments were designed with an orthogonal central composite design on the three variables using response surface methodology (RSM).

Results: For glucoamylase production, the optimum temperature and medium moisture content for the three fungi were 26.6°C and 71.8%, respectively. The optimum cultivation time for M. hiemalis and R. oryzae was 33.1 h, while it was 66.8 h for M. indicus. At optimum conditions, glucoamylase production by M. indicus, M. hiemalis, and R. oryzae was respectively 255.3, 272.3, and 1545.3 U per g dry substrate.

Conclusion: R. oryzae is a suitable candidate for industrial production of glucoamylase.

Downstream optimization of fungal-based simultaneous saccharification and fermentation relevant to lignocellulosic ethanol production

To support the inefficient limitation of long-term biosystem by well-known simultaneous saccharification and fermentation (SSF), electron beam irradiated rice straw (at 80 kGy, 1 MeV, and 0.12 mA) was fermented using fungal-based simultaneous saccharification and fermentation (FBSSF) by saprophytic zygomycetes Mucor indicus. Based on the growth optimization (by response surface methodology), this eco-friendly bioprocess either without metabolic inhibitors (especially furfurals and acetic acids) or byproducts (especially glycerols) significantly increased the biodegradability and fermentability of lignocellulosic rice straw. Specifically, when irradiated straw was simultaneously bioconverted by M. indicus for 48 h, the ethanol yield was 57.2% of the theoretical maximum. This value was on the similar level as the 59.8% (for 144 h) measured from processed straw by well-known SSF. Furthermore, after FBSSF for 144 h based on large-scale mass balance, the ethanol concentration and production yield, and productivity were 34.6 g/L, 72.3% of the theoretical maximum, and 0.24 g/L/h, respectively.