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.

Purification, Characterization, and Application of Endoglucanase from Rhizopus oryzae as Antibiofilm Agent

The enzyme endoglucanase is responsible for the depolymerization of cellulose. This study focuses on characterization and purification of endoglucanase from Rhizopus oryzae MTCC 9642 through a simple size exclusion method and its effective application as an antibiofilm agent. Extracellular ß-1,4-endoglucanase, an enzyme that catalyzes the hydrolysis of carboxymethyl cellulose, was found to be synthesized by Rhizopus oryzae MTCC 9642. The enzyme was purified up to homogeneity simply by size exclusion process through ultrafiltration and gel chromatography. The molecular weight of purified enzyme protein was estimated to be 39.8 kDa and it showed the highest substrate affinity towards carboxymethyl-cellulose with Km and Vmax values of 0.833 mg ml-1 and of 0.33 mmol glucose min-1 mg-1protein, respectively. The purified enzyme exhibited optimal activity at pH 6 with a broad stability range of pH 3-8. The most preferred temperature was 35 °C and 50% of activity could be retained after the thermal exposure at 40 °C for 25 min. The purified enzyme protein was inactivated by Cu2+, while the activity could be enhanced by the addition of exogenous thiols. Since biofilm is a challenge for health sector, with the aim of eradicating the biofilm, the purified endoglucanase was used to remove biofilm produced by two nosocomial bacteria. As predicted by in silico molecular docking interaction, the purified enzyme could effectively degrade biofilm architecture of bacterial strains S. aureus and P. aeruginosa by 76.52 ± 6.52% and 61.67 ± 8.76%, respectively. The properties of purified enzyme protein, as elucidated by in vitro and in silico characterization, may be favourable for its commercial applications as a potent antibiofilm agent.

Rhizopus stolonifer biomass catalytic transesterification capability: optimization of cultivation conditions

BACKGROUND

Using fungal biomass for biocatalysis is a potential solution for the expensive cost of the use o enzymes. Production of fungal biomass with effective activity requires optimizing the cultivation conditions.

RESULTS

Rhizopus stolonifer biomass was optimized for transesterification and hydrolysis of waste frying oil (WFO). Growth and biomass lipolytic activities of R. stolonifer improved under shaking conditions compared to static conditions, and 200 rpm was optimum. As biomass lipase and transesterification activities inducer, olive oil was superior to soybean, rapeseed, and waste frying oils. Biomass produced in culture media containing fishmeal as an N-source feedstock had higher lipolytic capabilities than corn-steep liquor and urea. Plackett Burman screening of 9 factors showed that pH (5-9), fishmeal (0.25-1.7%, w/v), and KH2PO4 (0.1-0.9%, w/v) were significant factors with the highest main effect estimates 11.46, 10.42, 14.90, respectively. These factors were selected for response surface methodology (RSM) optimization using central composite design (CCD). CCD models for growth, biomass lipase activity, and transesterification capability were significant. The optimum conditions for growth and lipid modification catalytic activities were pH 7.4, fishmeal (2.62%, w/v), and KH2PO4 (2.99%, w/v).

CONCLUSION

Optimized culture conditions improved the whole cell transesterification capability of Rhizopus stolonifer biomass in terms of fatty acid methyl ester (FAME) concentration by 67.65% to a final FAME concentration of 85.5%, w/w.

Nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry metabolomics studies on non-organic soybeans versus organic soybeans (Glycine max), and their fermentation by Rhizopus oligosporus

BACKGROUND

Soybeans (Glycine max) are high in proteins and isoflavones, which offer many health benefits. It has been suggested that the fermentation process enhances the nutrients in the soybeans. Organic foods are perceived as better than non-organic foods in terms of health benefits, yet little is known about the difference in the phytochemical content that distinguishes the quality of organic soybeans from non-organic soybeans. This study investigated the chemical profiles of non-organic (G, T, U, UB) and organic (C, COF, A, R, B, Z) soybeans (G. max [L.] Merr.) and their metabolite changes after fermentation with Rhizopus oligosporus.

RESULTS

A clear separation was only observed between non-organic G and organic Z, which were then selected for further investigation in the fermentation of soybeans (GF and ZF). All four groups (G, Z, GF, ZF) were analyzed using nuclear magnetic resonance (NMR) spectroscopy along with liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this way a total of 41 and 47 metabolites were identified respectively, with 12 in common. A clear variation (|log_1.5 FC| > 2 and P < 0.05) was observed between Z and ZF: most of the sugars and isoflavone glycosides were found only in Z, while more amino acids and organic acids were found in ZF. An additional four metabolites clustered as C-glycosylflavonoids were discovered from MS/MS-based molecular networking.

CONCLUSION

Chemical profiles of non-organic and organic soybeans exhibited no significant difference. However, the metabolite profile of the unfermented soybeans, which were higher in sugars, shifted to higher amino acid and organic acid content after fermentation, thereby potentially enhancing their nutritional value. © 2022 Society of Chemical Industry.

Production of Primary Metabolites by Rhizopus stolonifer, Causal Agent of Almond Hull Rot Disease

Species in the fungal genus Rhizopus are able to convert simple sugars into primary metabolites such as fumaric acid, lactic acid, citric acid, and, to a lesser extent, malic acid in the presence of specific carbon and nitrogen sources. This ability has been linked to plant pathogenicity. Rhizopus stolonifer causes hull rot disease in almonds, symptoms of which have been previously associated with the fungus's production of fumaric acid. Six isolates of R. stolonifer taken from infected almond hulls were grown in artificial media amended with one of four carbon sources (glucose, fructose, sucrose, and xylose) and two nitrogen sources (asparagine and ammonium sulphate) chosen based on almond hull composition and used in industry. Proton nuclear magnetic resonance (1H NMR)-based metabolomics identified that R. stolonifer could metabolise glucose, fructose, sucrose, and to a lesser extent xylose, and both nitrogen sources, to produce three metabolites, i.e., fumaric acid, lactic acid, and ethanol, under in vitro conditions. Sugar metabolisation and acid production were significantly influenced by sugar source and isolates, with five isolates depleting glucose most rapidly, followed by fructose, sucrose, and then xylose. The maximum amounts of metabolites were produced when glucose was the carbon source, with fumaric acid produced in higher amounts than lactic acid. Isolate 19A-0069, however, preferred sucrose as the carbon source, and Isolate 19A-0030 produced higher amounts of lactic acid than fumaric acid. This is the first report, to our knowledge, of R. stolonifer producing lactic acid in preference to fumaric acid. Additionally, R. stolonifer isolate 19-0030 was inoculated into Nonpareil almond fruit on trees grown under high- and low-nitrogen and water treatments, and hull compositions of infected and uninfected fruit were analysed using 1H NMR-based metabolomics. Glucose and asparagine content of uninfected hulls was influenced by the nitrogen and water treatments provided to the trees, being higher in the high-nitrogen and water treatments. In infected hulls, glucose and fructose were significantly reduced but not sucrose or xylose. Large amounts of both fumaric and lactic acid were produced, particularly under high-nitrogen treatments. Moreover, almond shoots placed in dilute solutions of fumaric acid or lactic acid developed leaf symptoms very similar to the 'strike' symptoms seen in hull rot disease in the field, suggesting both acids are involved in causing disease.

Rhizopus oryzae fermentation wastewater nutrient removal coupling protein fodder production by employing Chlorella pyrenoidosa

The scenario was to investigate feasibilities of employing Chlorella pyrenoidosa for Rhizopus oryzae fermentation wastewater nutrient removal coupling protein fodder production. Results stated that TN, TP, NH₃-N, COD, BOD removal reached 99.79%, 94.70%, 98.80%, 97.60%, 99.60% to acquire discharge permit under fed-batch manipulation, whilst the peaked protein yield (19.94 g/L) was 6.04-fold more than batch manipulation. Rhizopus oryzae fermentation wastewater feeding C. pyrenoidosa was praised as high-quality protein not only with 26.78% essential amino acids and essential amino acids/nonessential amino acids value of 0.84 but also pathogenic bacteria and heavy metal loads complying with fodder standards. In vitro digestibility of dry matter, protein, lipid, and starch achieving 80.07%, 92.13%, 95.93%, 91.9% and bioavailability of polypeptides, triglycerides, free fatty acids, and oligosaccharides displaying 98.67%, 87.12%, 93.86%, 30.21%, which were roughly-equivalent to corn/soybean fodder. The findings formed exemplifications in utilizing other microalgal systems for wastewater nutrient removal coupling chemicals production.

A metabolomics approach to evaluate post-fermentation enhancement of daidzein and genistein in a green okara extract

BACKGROUND

Okara is a major agri-industrial by-product of the tofu and soymilk industries. Employing food-wastes as substrates for the green production of natural functional compounds is a recent trend that addresses the dual concepts of sustainable production and a zero-waste ecosystem.

RESULTS

Extracts of unfermented okara and okara fermented with Rhizopus oligosporus were obtained using ethanol as extraction solvent, coupled with ultrasound sonication for enhanced extraction. Fermented extracts yielded significantly better results for total phenolic content (TPC) and total flavonoid content (TFC) than unfermented extracts. A qualitative liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis revealed a shift from glucoside forms to respective aglycone forms of the detected isoflavones, post-fermentation. Since the aglycone forms have been associated with numerous health benefits, a quantitative high-performance liquid chromatography (HPLC) analysis was performed. Fermented okara extracts had daidzein and genistein concentrations of 11.782 ± 0.325 μg mL-1 and 10.125 ± 1.028 μg mL-1 , as opposed to that of 6.7 ± 2.42 μg mL-1 and 4.55 ± 0.316 μg mL-1 in raw okara extracts, respectively. Lastly, the detected isoflavones were mapped to their metabolic pathways, to understand the biochemical reactions triggered during the fermentation process.

CONCLUSION

Fermented okara may be implemented as a sustainable solution for production of natural bioactive isoflavonoids genistein and daidzein. © 2021 Society of Chemical Industry.

Propeptide in Rhizopus chinensis Lipase: New Insights into Its Mechanism of Activity and Substrate Selectivity by Computational Design

Most fungal lipases contain a propeptide, which is very important for their function and substrate selectivity. In the present study, Rhizopus chinensis lipase (RCL) was used as a research model to explore the mechanism of the propeptide of the lipase. Conventional molecular dynamics (MD) and metadynamics simulations were used to explore the mechanism by which the propeptide affects the activity of the lipase, which was subsequently verified by mutation experiments. MD simulations indicated that the propeptide had an inhibitory effect on the lid movement of RCL and found a key region (Val5-Thr10) on the propeptide. Subsequently, site-directed mutations were created in this region. The mutations enhanced the lipase catalytic efficiency to 700% and showed the potential for the propeptide to shift the substrate specificity of RCL. The specificity and activity of RCL mutants also had similar trends to wild-type RCL toward triglycerides with varying chain lengths. The mutual corroboration of simulation and site-directed mutagenesis results revealed the vital role of the key propeptide region in the catalytic activity and substrate specificity of the lipase.

Fermentation with Edible Rhizopus Strains to Enhance the Bioactive Potential of Hull-Less Pumpkin Oil Cake

Solid-state fermentation with food-grade fungal strains can be applied to enhance the bioactive parameters of agro-industrial by-products. Tempe-type fermentation can be adapted to various substrates, but the key factor is the appropriate strain selection. The aim of this study was to compare the potential of Rhizopus strains for obtaining products of improved antioxidant activity from pumpkin oil cake. For this purpose, substances reacting with the Folin-Ciocalteu reagent, with free radical scavenging potential, as well as reducing power were assessed. The effect of the fermentation on the phytate level and inositol phosphate profile in the material was also monitored. The fermentation resulted in the significant enhancement of the antioxidant potential of pumpkin oil cake in the case of all the strains tested, but the most efficient one was R. oligosporus ATCC 64063. During the course of fermentation, the level of phytate in the material decreased (the highest reduction rate was observed in the oil cake fermented with R. oryzae CBS 372.63), while peptides and fungal glucosamine were accumulated. Tempe-type fermentation can be considered as an alternative way of improving the bioactive parameters of pumpkin oil cake and, thanks to the various activities of different Rhizopus strains, it is possible to obtain products of desired parameters.

Rhizopus oligosporus and Lactobacillus plantarum Co-Fermentation as a Tool for Increasing the Antioxidant Potential of Grass Pea and Flaxseed Oil-Cake Tempe

Tempe-type fermentation originating from Indonesia can enhance the antioxidant activity of plant material. However, this biological potential depends on substrates and applied microorganisms. This study aimed to determine whether co-fermentation with Rhizopus oligosporus and Lactobacillus plantarum improved antioxidant activity of tempe obtained from grass pea seeds with flaxseed oil-cake addition (up to 30%). For this purpose, substances reacting with Folin-Ciocalteu reagent and free radicals scavenging potential were measured in water-soluble fractions and dialysates from simulated in vitro digestion. Additionally, the water-soluble phenolic profile was estimated. The higher level of water-extractable compounds with antioxidant activity was determined in co-fermentation products than in fungal fermentation products. Moreover, the fermentation process with the use of L. plantarum contributed to a greater accumulation of some phenolic acids (gallic acid, protocatechuic acid) in tempe without having a negative effect on the levels of other phenolic compounds determined in fungal fermented tempe. During in vitro digestion simulating the human digestive tract, more antioxidant compounds were released from products obtained after co-fermentation than fungal fermentation. An addition of 20% flaxseed oil-cake and the application of bacterial-fungal co-fermentation, can be considered as an alternative tool to enhance the antioxidant parameters of grass pea tempe.

Isolation and identification of the antimicrobial substance included in tempeh using Rhizopus stolonifer NBRC 30816 for fermentation

In this study, we focus on the antimicrobial properties of tempeh, a soybean fermented food, against oral bacteria. Tempeh showed antimicrobial activity against dental caries pathogenic bacterium Streptococcus mutans at a final concentration of 1 mg/mL. An antimicrobial substance contained in tempeh was present in the 100 kDa or greater fraction generated by ultrafiltration, but it was found not to be proteinaceous by native-PAGE, SDS-PAGE and protein degradation tests. Next, when the fraction was purified with an ODS column, the 80% and 100% methanol eluates showed antimicrobial activity against S. mutans. The 100% methanol eluate was further subjected to a 2nd column purification, and isolation of the target was confirmed by HPLC. When the isolated material was analyzed by ESI-MS, the m/z was 279.234. Further analysis by Raman spectroscopy revealed a peak similar to linoleic acid. This substance also possessed antimicrobial properties equivalent to linoleic acid.

Linoleic acid, α-linolenic acid, and monolinolenins as antibacterial substances in the heat-processed soybean fermented with Rhizopus oligosporus

Antibacterial activities against Staphylococcus aureus and Bacillus subtilis were found in an ethanol fraction of tempe, an Indonesian fermented soybean produced using Rhizopus oligosporus. The ethanol fraction contained free fatty acids, monoglycerides, and fatty acid ethyl esters. Among these substances, linoleic acid and α-linolenic acid exhibited antibacterial activities against S. aureus and B. subtilis, whereas 1-monolinolenin and 2-monolinolenin exhibited antibacterial activity against B. subtilis. The other free fatty acids, 1-monoolein, monolinoleins, ethyl linoleate, and ethyl linolenate did not exhibit bactericidal activities. These results revealed that R. oligosporus produced the long-chain polyunsaturated fatty acids and monolinolenins as antibacterial substances against the Gram-positive bacteria during the fungal growth and fermentation of heat-processed soybean.

Effect of Rhizopus nigricans (Rhizopus stolonifera)-based novel starter culture on quality and safety attributes of doenjang, a traditional Korean soybean fermented food product

We aimed to develop a consortium of starter culture of effective microorganisms to prepare doenjang, a traditional Korean fermented food. Different ratios of Bacillus subtilis TKSP 24 (B), Aspergillus oryzae complex (A), Rhizopus nigricans (also named as Rhizopus stolonifera) (R), and Mucor racemosus 15 (M15) were selected as meju starter cultures to produce doenjang with improved quality. Microbial strain combinations (B: A: R and B: M15: R) were mixed separately at three different ratios [1:1:1 (w/w), 1:0.5:1.5 (w/w), and 1:1.5:0.5 (w/w)] to prepare BAR-1, BAR-2, BAR-3, BM15R-1, BM15R-2, and BM15R-3 doenjang samples. Quantitative analyses included free amino acids, free sugar, volatile and non-volatile organic acids, cellular antioxidant activity along with the presence of biogenic amines and aflatoxins, and microbial counts. Total free amino acids responsible for the sweet taste of doenjang were highest in BAR-2 (322.50 mg/100 g) and BM15R-3 (320.07 mg/100 g). Total volatile organic acid was highest in BAR-1 compared to other preparations. All doenjang samples had biogenic amines, especially histamine, below the toxicity level (500 mg/kg). Also, the aflatoxin and hazardous microbial count in the tested doenjang samples were below the level of toxicity. The findings suggest that use of multiple microbial strains in combination with R. nigricans as a starter culture could be a novel and effective approach to improve the nutrition and safety of fermented soybean food products of doenjang.

Evaluation of quantity and quality of chitosan produce from Rhizopus oryzae by utilizing food product processing waste whey and molasses

Low cost whey salt medium (WSM) and molasses salt medium (MSM) have been constructed utilizing food processing byproduct whey and molasses for the production of bio-polysaccharide chitosan from Rhizopus oryzae and subsequently comprehensive physico-chemical characterization of the fungal chitosan has been carried out using various analytical tools to apprehend its biochemical utility. Same has been repeated with chitosan from conventional potato dextrose broth (PDB) for comparison purpose. The yields of chitosan in three different media were 0.62 (WSM), 0.39 (MSM) and 0.63 (PDB) g/L respectively. Molecular weights of the chitosans were in the range of 100-300 kDa. WSM-chitosan and MSM-chitosan were less polydispersed, possessed more hydrated polymorph and loose crystal packing than PDB-chitosan. This indicate that WSM-chitosan and MSM-chitosan are highly exposed to the external reagent hence more reactive to the external reagents with compare to PDB-chitosan. Literature suggest isolated chitosans are useful for specific drug delivery applications.

Neuroprotective effect of tempeh against lipopolysaccharide-induced damage in BV-2 microglial cells

Objectives: This study evaluated the bioactive composition of tempeh products and examined the effects of tempeh on BV-2 microglial cell cytotoxicity, neurotrophic effects, and expression of inflammatory genes.Methods: Tempeh products included soybean fermented by Rhizopus, soybean fermented through cocultivation with Rhizopus and Lactobacillus, and red bean fermented through cocultivation with Rhizopus and Lactobacillus (RT-C). We analyzed the bioactive contents of tempeh extracts and evaluated the effects of tempeh water extract on lipopolysaccharide (LPS)-treated BV-2 cells.Results: The results showed that RT-C water extract had the highest concentrations of γ-aminobutyric acid (GABA) and anthocyanin. The tempeh water extracts, especially RT-C, reduced the formation of LPS-induced reactive oxygen species, downregulated the levels of nitric oxide synthase and phospho-cyclic-AMP response element-binding protein, and upregulated the expression of brain-derived neurotrophic factor (BDNF).Discussion: Our data demonstrate that RT-C has the highest concentrations of GABA and anthocyanin, more effectively reduces oxidative stress and inflammation, and increases the expression of BDNF in LPS-induced BV-2 cells.

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.

Microwave-assisted extraction of chitosan from Rhizopus oryzae NRRL 1526 biomass

Microwave-assisted extraction (MAE) of chitosan from dried fungal biomass of Rhizopus oryzae NRRL1526, obtained by culturing on potato dextrose broth (PDB), was performed and the optimal conditions required were identified using statistical analysis for the first time in this study. This microwave-assisted extraction (MAE) was compared against the conventional autoclave assisted method of chitosan extraction. The full factorial experimental design was used to investigate the impact of operating parameters of MAE, microwave power (100 W-500 W), and duration (10 min-30 min), on alkaline insoluble material (AIM) yield, chitosan yield, and degree of deacetylation (DDA). The effect of operating conditions was then evaluated using full factorial data analysis and optimum condition for MAE of chitosan was identified using response surface methodology to be 300 W and 22 min. This optimum condition identified was then further evaluated and the chitosan obtained characterized. Higher chitosan yield of 13.43 ± 0.3% (w/w) of fungal biomass was obtained when compared to that obtained, 6.67% ± 0.3% (w/w) of dry biomass, for the conventional extraction process. MAE yielded chitosan of higher degree of deacetylation, 94.6 ± 0.9% against 90.6 ± 0.5% (conventional heating), but the molecular weight was observed to be similar to that obtained by using conventional autoclave heating. MAE of chitosan was observed to yield a higher quantity of chitosan when compared to conventional extraction process and obtained chitosan exhibited a higher degree of deacetylation as well as molecular weight. The lower energy consumption of 0.11 kW h for MAE (5 kW h for conventional process) and the concomitant reduction in the energy bill to 1.1 cents from 50 cents, in addition to the above results, show that microwave irradiation is a more efficient and environment-friendly means to obtain chitosan from fungal biomass.

Anti-Inflammatory 18β-Glycyrrhetinin Acid Derivatives Produced by Biocatalysis

In this study, the biocatalysis of 18β-glycyrrhetinic acid by two strains of filamentous fungi, namely Rhizopus arrhizus AS 3.2893 and Circinella muscae AS 3.2695, was investigated. Scaled-up biotransformation reactions yielded 14 metabolites. Their structures were established based on extensive nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data analyses, and seven of them are new compounds. The two fungal strains exhibited distinct biocatalytic features. R. arrhizus could catalyze hydroxylation and carbonylation reactions, whereas C. muscae preferred to catalyze hydroxylation and glycosidation reactions. These highly specific reactions are difficult to achieve by chemical synthesis, particularly under mild conditions. Furthermore, we found that most of the metabolites exhibited pronounced inhibitory activities on lipopolysaccharides-induced nitric oxide production in RAW264.7 cells. These biotransformed derivatives of 18β-glycyrrhetinic acid could be potential anti-inflammatory agents.

Production of various organic acids from different renewable sources by immobilized cells in the regimes of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SFF)

The study was aimed at production of different organic acids (OA) (lactic, fumaric, or succinic) by various microbial cells (filamentous fungi Rhizopus oryzae (F-814, F-1127) and bacteria Actinobacillus succinogenes B-10111) immobilized into poly(vinyl alcohol) (PVA) cryogel from diverse renewable raw materials (wheat and rice straw, aspen and pine sawdust, Jerusalem artichoke stems and tubers, biomass of macro- and microalgae) under batch conditions. The process productivity, bulk output and OA concentrations were higher in case of using immobilized cells than in case of free cells under identical conditions. A higher OA productivity was reached via simultaneous enzymatic saccharification and microbial fermentation (SSF) of same raw materials as compared to their separate enzymatic hydrolysis and fermentation of accumulated reducing sugars (SHF). Maximal concentrations of all OAs studied were obtained for bioconversion of Jerusalem artichoke tubers. The immobilized cells were used in long-term conversion of various renewable materials to OAs in SSF.

An integrated metagenomic/metaproteomic investigation of microbiota in dajiang-meju, a traditional fermented soybean product in Northeast China

Dajiang-meju have been used as major ingredients for the preparation of traditional spontaneously fermented soybean paste in Northeast China. In this work, we sequenced and analyzed the metagenome of 12 dajiang-meju samples. To complement the metagenome analysis, we analyzed the taxonomic and functional diversity of the microbiota by metaproteomics (LC-MS/MS). The analysis of metagenomic data revealed that the communities were primarily dominated by Enterobacter, Enterococcus, Leuconostoc, Lactobacillus, Citrobacter and Leclercia. Moreover, changes in the functional levels were monitored, and metaproteomic analysis revealed that most of the proteins were mainly expressed by members of Rhizopus, Penicillium and Geotrichum. The number of sequences allocated to fungi in the fermentation process decreased, whereas the number of sequences assigned to bacteria increased with time of fermentation. In addition, functional metagenomic profiling indicated that a series of sequences related to carbohydrates and amino acids metabolism were enriched. Additionally, enzymes associated with glycolysis metabolic pathways were presumed to contribute to the generation of flavor in dajiang-meju. Proteins from different dajiang-meju samples involved in global and overview maps, carbohydrate metabolism, nucleic acid metabolism and energy metabolism were differentially expressed. This information improves the understanding of microbial metabolic patterns with respect to the metaproteomes of dajiang-meju and provides a powerful tool for studying the fermentation process of soybean products.

Controlled fermentation of rapeseed presscake by Rhizopus, and its effect on some components with relevance to human nutrition

The use of rapeseed protein could contribute to meeting the increasing demand for plant proteins with high biological value in human nutrition. In order to make rapeseed presscake fit for human consumption, the presscake was fermented by using the tempeh mould, Rhizopus microsporus var. oligosporus. Fermentation was satisfactory at initial levels of added acetic acid of 40-60 mmoles/Kg, a_w of 0.97, pasteurization, surface inoculation and incubation at 32 °C and 90-95% relative humidity. It was crucial to stop the fermentation once the mould had grown and metabolized sufficiently but before a major rise in pH and subsequent growth of acid-sensitive sporeforming bacteria occurred. Some degradation of glucosinolates, cell wall polysaccharides and phenolic compounds was found, but there was some evidence that growth and metabolism of the mould also depended on the texture of the presscake, as these factors affect the oxygen supply to the mould. In conclusion, it is possible to ferment rapeseed presscake by using the "Tempeh starter" Rhizopus oligosporus, but in order to use the resulting product to enrich various foods with protein or replace other proteins, the degree of degradation of undesired compounds should be further standardized, especially by the control of the pH, oxygen supply, and fermentation time.

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

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

Antifungal effect of phenolic extract of fermented rice bran with Rhizopus oryzae and its potential use in loaf bread shelf life extension

BACKGROUND

In this study the antifungal potential of a phenolic extract obtained from rice bran fermented with Rhizopus oryzae CECT 7560 and its application in the elaboration of bread was assessed.

RESULTS

Eighteen compounds with antifungal potential were identified by LC-ESI-qTOF-MS in the extract: organic acids, gallates and gallotannins, flavonoids, ellagic acid and benzophenone derivatives. The extract was active against strains of Fusarium, Aspergillus and Penicillium, with minimum inhibitory concentration ranging from 390 to 3100 µg mL^-1 and minimum fungicidal concentration variable from 780 to 6300 µg mL^-1 . The strains that were most sensitive to the phenolic extract were F. graminearum, F. culmorum, F. poae, P. roqueforti, P. expansum and A. niger. The phenolic extract added at 5 and 1 g kg^-1 concentrations in the preparation of bread loaves contaminated with P. expansum produced a reduction of 0.6 and 0.7 log CFU g^-1 . The bread loaves treated with calcium propionate and 10 g kg^-1 of the phenolic extract evidenced an improvement in their shelf lives of 3 days.

CONCLUSION

The phenolic extract assessed in this study could be considered as an alternative for inhibiting toxigenic fungi and as a substitute for synthetic compounds in food preservation. © 2018 Society of Chemical Industry.

Analysis of Improved Nutritional Composition of Potential Functional Food (Okara) after Probiotic Solid-State Fermentation

Okara is a major agro-waste, generated as a byproduct from the soymilk and tofu industry. Since okara has a high nutritive value, reusing it as a substrate for solid state biofermentation is an economical and environmental friendly option. Rhizopus oligosporus and Lactobacillus plantarum were the probiotic FDA-approved food-grade cultures used in this study. The study revealed that biofermenting okara improves its nutritional composition. It was found that the metabolomic composition (by GC-MS analysis) and antioxidant activity (by DPPH test) improved after the microbial fermentations. Of the two, okara fermented with R. oligosporus showed better results. Further, the metabolites were traced back to their respective biosynthesis pathways, in order to understand the biochemical reactions being triggered during the fermentation processes. The findings of this entire work open up the possibility of employing fermented okara as a potential functional food for animal feed.

An optimized fed-batch culture strategy integrated with a one-step fermentation improves L-lactic acid production by Rhizopus oryzae

In previous work, we proposed a novel modified one-step fermentation fed-batch strategy to efficiently generate L-lactic acid (L-LA) using Rhizopus oryzae. In this study, to further enhance efficiency of L-LA production through one-step fermentation in fed-batch cultures, we systematically investigated the initial peptone- and glucose-feeding approaches, including different initial peptone and glucose concentrations and maintained residual glucose levels. Based on the results of this study, culturing R. oryzae with initial peptone and glucose concentrations of 3.0 and 50.0 g/l, respectively, using a fed-batch strategy is an effective approach of producing L-LA through one-step fermentation. Changing the residual glucose had no obvious effect on the generation of L-LA. We determined the maximum LA production and productivity to be 162 g/l and 6.23 g/(l·h), respectively, during the acid production stage. Compared to our previous work, there was almost no change in L-LA production or yield; however, the productivity of L-LA increased by 14.3%.

Fungal and herbivore elicitation of the novel maize sesquiterpenoid, zealexin A4, is attenuated by elevated CO2

Chemical isolation and NMR-based structure elucidation revealed a novel keto-acidic sesquiterpenoid, termed zealexin A4 (ZA4). ZA4 is elicited by pathogens and herbivory, but attenuated by heightened levels of CO ₂ . The identification of the labdane-related diterpenoids, termed kauralexins and acidic sesquiterpenoids, termed zealexins, demonstrated the existence of at least ten novel stress-inducible maize metabolites with diverse antimicrobial activity. Despite these advances, the identity of co-occurring and predictably related analytes remains largely unexplored. In the current effort, we identify and characterize the first sesquiterpene keto acid derivative of β-macrocarpene, named zealexin A4 (ZA4). Evaluation of diverse maize inbreds revealed that ZA4 is commonly produced in maize scutella during the first 14 days of seedling development; however, ZA4 production in the scutella was markedly reduced in seedlings grown in sterile soil. Elevated ZA4 production was observed in response to inoculation with adventitious fungal pathogens, such as Aspergillus flavus and Rhizopus microsporus, and a positive relationship between ZA4 production and expression of the predicted zealexin biosynthetic genes, terpene synthases 6 and 11 (Tps6 and Tps11), was observed. ZA4 exhibited significant antimicrobial activity against the mycotoxigenic pathogen A. flavus; however, ZA4 activity against R. microsporus was minimal, suggesting the potential of some fungi to detoxify ZA4. Significant induction of ZA4 production was also observed in response to infestation with the stem tunneling herbivore Ostrinia nubilalis. Examination of the interactive effects of elevated CO₂ (E-CO₂) on both fungal and herbivore-elicited ZA4 production revealed significantly reduced levels of inducible ZA4 accumulation, consistent with a negative role for E-CO₂ on ZA4 production. Collectively, these results describe a novel β-macrocarpene-derived antifungal defense in maize and expand the established diversity of zealexins that are differentially regulated in response to biotic/abiotic stress.

Biosynthesis and Characterization of Zearalenone-14-Sulfate, Zearalenone-14-Glucoside and Zearalenone-16-Glucoside Using Common Fungal Strains

Zearalenone (ZEN) and its phase II sulfate and glucoside metabolites have been detected in food and feed commodities. After consumption, the conjugates can be hydrolyzed by the human intestinal microbiota leading to liberation of ZEN that implies an underestimation of the true ZEN exposure. To include ZEN conjugates in routine analysis, reliable standards are needed, which are currently not available. Thus, the aim of the present study was to develop a facilitated biosynthesis of ZEN-14-sulfate, ZEN-14-glucoside and ZEN-16-glucoside. A metabolite screening was conducted by adding ZEN to liquid fungi cultures of known ZEN conjugating Aspergillus and Rhizopus strains. Cultivation conditions and ZEN incubation time were varied. All media samples were analyzed for metabolite formation by HPLC-MS/MS. In addition, a consecutive biosynthesis was developed by using Fusarium graminearum for ZEN biosynthesis with subsequent conjugation of the toxin by utilizing Aspergillus and Rhizopus species. ZEN-14-sulfate (yield: 49%) is exclusively formed by Aspergillus oryzae. ZEN-14-glucoside (yield: 67%) and ZEN-16-glucoside (yield: 39%) are formed by Rhizopus oryzae and Rhizopusoligosporus, respectively. Purities of ≥73% ZEN-14-sulfate, ≥82% ZEN-14-glucoside and ≥50% ZEN-16-glucoside were obtained by ¹H-NMR. In total, under optimized cultivation conditions, fungi can be easily utilized for a targeted and regioselective synthesis of ZEN conjugates.

Metalaxyl Degradation by Mucorales Strains Gongronella sp. and Rhizopus oryzae

In this study, the degradation of metalaxyl was investigated in the presence of two Mucorales strains, previously isolated from soil subjected to repeated treatments with this fungicide and selected after enrichment technique. Fungal strains were characterised by a polyphasic approach using phylogenetic analysis of the Internal Transcribed Spacer (ITS) gene region, phenotypic characterisation by Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) spectral analysis, and growth kinetics experiments. The strains were identified as Gongronella sp. and Rhizopus oryzae. The fungal growth kinetics in liquid cultures containing metalaxyl fits with Haldane model. Under laboratory conditions, the ability of Gongronella sp. and R. oryzae cultures to degrade metalaxyl was evaluated in liquid cultures and soil experiments. Both species were able to: (a) use metalaxyl as the main carbon and energy source; and (b) degrade metalaxyl in polluted soils, with rates around 1.0 mg kg^-¹ d^-¹. This suggests these strains could degrade metalaxyl in soils contaminated with this fungicide.

Bioprocessing of common beans in diets for tilapia: in vivo digestibility and antinutritional factors

BACKGROUND

Bioprocessing of ingredients by solid-state fermentation is a low-cost technique for preparing diets. It is performed by adding microorganisms such as Rhizopus oligosporus to bean grains, achieving minimal degradation of nutrients and a significant improvement in digestibility. In particular, fermentation induces favorable changes in beans by reducing enzyme inhibitors, such as phytates and tannins.

RESULTS

Fermentation significantly (P < 0.05) increased the protein content and digestibility of dry matter and protein compared with whole bean grains, and decreased the content of lipids, ash and phytic acid. Hardening did not have a significant (P > 0.05) effect on the chemical content of beans and digestibility of diets. The dehulled bean meal significantly (P < 0.05) increased protein and lipid content and digestibility of dry matter and protein of beans, and decreased fiber, ash and tannin content. The chemical content of beans and digestibility of ingredients compare favorably with those reported by other authors, indicating the benefits of fermentation and dehulling.

CONCLUSION

We concluded that bean meal obtained from fermentation or dehulling represents a low-cost alternative for diets for tilapia. © 2017 Society of Chemical Industry.

The effect of fermented buckwheat on producing l-carnitine- and γ-aminobutyric acid (GABA)-enriched designer eggs

BACKGROUND

The potential of fermented buckwheat as a feed additive was studied to increase l-carnitine and γ-aminobutyric acid (GABA) in designer eggs. Buckwheat contains high levels of lysine, methionine and glutamate, which are precursors for the synthesis of l-carnitine and GABA. Rhizopus oligosporus was used for the fermentation of buckwheat to produce l-carnitine and GABA that exert positive effects such as enhanced metabolism, antioxidant activities, immunity and blood pressure control.

RESULTS

A novel analytical method for simultaneously detecting l-carnitine and GABA was developed using liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS. The fermented buckwheat extract contained 4 and 34 times more l-carnitine and GABA respectively compared with normal buckwheat. Compared with the control, the fermented buckwheat extract-fed group showed enriched l-carnitine (13.6%) and GABA (8.4%) in the yolk, though only l-carnitine was significantly different (P < 0.05). Egg production (9.4%), albumen weight (2.1%) and shell weight (5.8%) were significantly increased (P < 0.05). There was no significant difference in yolk weight, and total cholesterol (1.9%) and triglyceride (4.9%) in the yolk were lowered (P < 0.05).

CONCLUSION

Fermented buckwheat as a feed additive has the potential to produce l-carnitine- and GABA-enriched designer eggs with enhanced nutrition and homeostasis. These designer eggs pose significant potential to be utilized in superfood production and supplement industries. © 2016 Society of Chemical Industry.

The Rare Amino Acid Building Block 3-(3-furyl)-Alanine in the Formation of Non-ribosomal Peptides

Microorganisms have made considerable contributions to the production of peptide secondary metabolites, many of them with therapeutic potential eg, the fungus-derived immunosuppressant cyclosporine A and the antibiotic daptomycin originating from Streptomyces. Most of the medically used peptides are the :product of non-ribosomal peptide synthetases (NRPS), incorporating apart from proteinogenic also unique, non-proteinogenic amino acids into the peptides. An extremely rare such amino acid is 3-(3-furyl)-alanine. So far, only few peptides have been found that contain this residue, including the rhizonins, bingchamide B and endolides. The producer of the rhizonins was proven to be the bacterial endosymbiont Burkholderia endofungorum inside the fungus Rhizopus microsporus. The microbial origin, chemistry and bioactivity of the 3-(3-furyl)-alanine containing peptides are the focus of this review.

Metabolism of Quercetin and Naringenin by Food-Grade Fungal Inoculum, Rhizopus azygosporus Yuan et Jong (ATCC 48108)

Rhizopus azygosporus Yuan et Jong (ATCC 48108), a starter culture for fermented soybean tempeh, produces β-glucosidases that cleave flavonoid glycosides into aglycones during fermentation. However, recent data suggest that fermentation of a flavonoid glycoside-rich extract with this strain did not result in the production of aglycones. Thus, in this paper, flavonoid metabolism of this strain was investigated. Incubation of flavonoid aglycones, naringenin and quercetin, with R. azygosporus resulted in the production of flavonoid glucosyl-, hydroxyl-, and sulfo-conjugated derivatives. Naringenin was completely metabolized within 96 h into eriodictyol sulfate and eriodictyol glucoside, whereas quercetin was partially metabolized into quercetin glucoside, diglucoside, sulfate, and glucosyl-sulfate. Most of these metabolites were found to be excreted by the fungi into the culture medium. Toxicity analysis revealed that incubation with both quercetin and naringenin did not exert inhibitory effects on fungal growth. This study presents an interesting mechanism of fungal detoxification of flavonoids in foods.

Omics-based approaches reveal phospholipids remodeling of Rhizopus oryzae responding to furfural stress for fumaric acid-production from xylose

In order to relieve the toxicity of furfural on Rhizopus oryzae fermentation, the molecular mechanism of R. oryzae responding to furfural stress for fumaric acid-production was investigated by omics-based approaches. In metabolomics analysis, 29 metabolites including amino acid, sugars, polyols and fatty acids showed significant changes for maintaining the basic cell metabolism at the cost of lowering fumaric acid production. To further uncover the survival mechanism, lipidomics was carried out, revealing that phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol and polyunsaturated acyl chains might be closely correlated with R. oryzae's adapting to furfural stress. Based on the above omics analysis, lecithin, inositol and soybean oil were exogenously supplemented separately with an optimized concentration in the presence of furfural, which increased fumaric acid titer from 5.78g/L to 10.03g/L, 10.05g/L and 12.13g/L (increased by 73.5%, 73.8% and 110%, respectively). These findings provide a methodological guidance for hemicellulose-fumaric acid development.

Production of flavor compounds from olive mill waste by Rhizopus oryzae and Candida tropicalis

The purpose of this study was to investigate the production of flavor compounds from olive mill waste by microbial fermentation of Rhizopus oryzae and Candida tropicalis. Olive mill waste fermentations were performed in shake and bioreactor cultures. Production of flavor compounds from olive mill waste was followed by Gas Chromatography–Mass spectrometry, Gas chromatography- olfactometry and Spectrum Sensory Analysis^®. As a result, 1.73-log and 3.23-log cfu/mL increases were observed in the microbial populations of R. oryzae and C. tropicalis during shake cultures, respectively. C. tropicalis can produce a higher concentration of d-limonene from olive mill waste than R. oryzae in shake cultures. The concentration of d-limonene was determined as 185.56 and 249.54 μg/kg in the fermented olive mill waste by R. oryzae and C. tropicalis in shake cultures respectively. In contrast, R. oryzae can produce a higher concentration of d-limonene (87.73 μg/kg) d-limonene than C. tropicalis (11.95 μg/kg) in bioreactor cultures. Based on sensory analysis, unripe olive, wet towel, sweet aromatic, fermented aromas were determined at high intensity in olive mill waste fermented with R. oryzae meanwhile olive mill waste fermented with C. tropicalis had only a high intensity of unripe olive and oily aroma.

Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots

We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3×10⁵ cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines.

High-efficiency l-lactic acid production by Rhizopus oryzae using a novel modified one-step fermentation strategy

In this study, lactic acid fermentation by Rhizopus oryzae was investigated using the two different fermentation strategies of one-step fermentation (OSF) and conventional fermentation (CF). Compared to CF, OSF reduced the demurrage of the production process and increased the production of lactic acid. However, the qp was significantly lower than during CF. Based on analysis of μ, qs and qp, a novel modified OSF strategy was proposed. This strategy aimed to achieve a high final concentration of lactic acid, and a high qp by R. oryzae. In this strategy, the maximum lactic acid concentration and productivity of the lactic acid production stage reached 158g/l and 5.45g/(lh), which were 177% and 366% higher, respectively, than the best results from CF. Importantly, the qp and yield did not decrease. This strategy is a convenient and economical method for l-lactic acid fermentation by R. oryzae.

Using tobacco waste extract in pre-culture medium to improve xylose utilization for l-lactic acid production from cellulosic waste by Rhizopus oryzae

The aim of this work was to study the high-titer l-lactic acid production from cellulosic waste using Rhizopus oryzae. The tobacco waste water-extract (TWE) added with 5g/L glucose and 0.1g/L vitamin C was optimized as pre-culture medium for R. oryzae. Results found that compared to traditional pre-culture medium, it improved xylose consumption rate up to 2.12-fold and enhanced l-lactic acid yield up to 1.73-fold. The highest l-lactic acid concentration achieved was 173.5g/L, corresponding to volumetric productivity of 1.45g/Lh and yield of 0.860g/g total reducing sugar in fed-batch fermentation. This process achieves efficient production of polymer-grade l-lactic acid from cellulosic feedstocks, lowers the cost of fungal cell pre-culture and provides a novel way for re-utilization of tobacco waste.

Biotransformation and molecular docking studies of aromatase inhibitors

Bioconversion of the aromatase inhibitor formestane (4-hydroxyandrost-4-ene-3,17-dione) (1) by the fungus Rhizopus oryzae ATCC 11145 resulted in a new minor metabolite 3,5α-dihydroxyandrost-2-ene-4,17-dione (2) and the known 4β,5α-dihydroxyandrostane-4,17-dione (3) as the major product. The structural elucidation and bioactivities of these metabolites are reported herein. Molecular modeling studies of the interactions between these metabolites and the aromatase protein indicated that acidic (D309), basic (R115), polar (T310), aromatic (F134, F221, and W224), and non-polar (I133, I305, A306, V369, V370, L372, V373, M374, and L477) amino acid residues contribute important interactions with the steroidal substrates. These combined experimental and theoretical studies provide fresh insights for the further development of more potent aromatase inhibitors.

Enrichment of two isoflavone aglycones in black soymilk by Rhizopus oligosporus NTU 5 in a plastic composite support bioreactor

BACKGROUND

A plastic composite support (PCS) bioreactor was implemented to evaluate the effects on isoflavone deglycosylation in black soymilk fermented by Rhizopus oligosporus NTU 5.

RESULTS

Evaluation for the optimal PCS for mycelia immobilisation was conducted, which led to the significant results that the most mycelium weight (0.237 g per PCS, P < 0.05) is held by an S-type PCS; therefore, it was selected for black soymilk fermentation. It was found that the PCS fermentation system without pH control exhibits better efficiency of isoflavone bioconversion (daidzin to daidzein, and genistin to genistein) than the one with pH control at pH 6.5. As for the long-run fermentation, those without pH control indeed accelerate the isoflavone bioconversion by continuously releasing β-glucosidase into soymilk. Deglycosylation can be completed in 8 to 24 h and sustained for at least 34 days as 26 batches. The non-pH-control fermentation system also exhibits the highest total phenolic content (ranged from 0.147 to 0.340 mg GAE mL(-1) sample) when compared to the pH-controlled and suspended ones. Meanwhile, the black soymilk from the 22nd batch with 8 h fermentation demonstrated the highest DPPH radical scavenging effect (54.7%).

CONCLUSION

A repeated-batch PCS fermentation system was established to accelerate the deglycosylation rate of isoflavone in black soymilk. © 2015 Society of Chemical Industry.

Effect of Fungi Fermentation on Organoleptic Properties, Energy Content and In-vitro Multienzyme Digestibility of Cassava Products (Flour & Gari)

The present study sought to investigate the effect of fungi fermentation on the energy content, sensory quality and the digestibility (in vitro) of cassava products (flour and gari). The fungi fermented cassava products (gari and flour) were produced, by fermenting cassava mash with pure strains of some common saprophytes, namely, Aspergillus flavus, Aspergillus niger, Rhizopus oryzae and Saccharomyces spp (Baker's yeast and palm wine yeast) for 72hrs before processing into cassava flour and gari, the forms in which cassava is popularly consumed in Nigeria. Parameters determined include energy (Bomb calorimetry), digestibility (in vitro) and sensory quality by trained taste panel. The results of the study indicated that fungi fermentation of the cassava mash significantly (P < 0.05) increased the acceptability of the colour, texture, aroma and taste of the “gari”, with that of Rhizopus oryzae fermentation having the highest general acceptability. Furthermore, the results also indicated that fungi fermentation of cassava mash significantly increased (P < 0.05) the in vitro multienzyme protein digestibility of the cassava products. In view of this, fungi fermentation could be used to improve the sensory quality and protein digestibility of cassava products without any significant (P > 0.05) effect on the energy-giving role of cassava products.

The Role of Aquaporins in pH-Dependent Germination of Rhizopus delemar Spores

Rhizopus delemar and associated species attack a wide range of fruit and vegetables after harvest. Host nutrients and acidic pH are required for optimal germination of R. delemar, and we studied how this process is triggered. Glucose induced spore swelling in an acidic environment, expressed by an up to 3-fold increase in spore diameter, whereas spore diameter was smaller in a neutral environment. When suspended in an acidic environment, the spores started to float, indicating a change in their density. Treatment of the spores with HgCl2, an aquaporin blocker, prevented floating and inhibited spore swelling and germ-tube emergence, indicating the importance of water uptake at the early stages of germination. Two putative candidate aquaporin-encoding genes-RdAQP1 and RdAQP2-were identified in the R. delemar genome. Both presented the conserved NPA motif and six-transmembrane domain topology. Expressing RdAQP1 and RdAQP2 in Arabidopsis protoplasts increased the cells' osmotic water permeability coefficient (Pf) compared to controls, indicating their role as water channels. A decrease in R. delemar aquaporin activity with increasing external pH suggested pH regulation of these proteins. Substitution of two histidine (His) residues, positioned on two loops facing the outer side of the cell, with alanine eliminated the pH sensing resulting in similar Pf values under acidic and basic conditions. Since hydration is critical for spore switching from the resting to activate state, we suggest that pH regulation of the aquaporins can regulate the initial phase of R. delemar spore germination, followed by germ-tube elongation and host-tissue infection.

Impacts of lignocellulose-derived inhibitors on L-lactic acid fermentation by Rhizopus oryzae

Inhibitors generated in the pretreatment and hydrolysis of corn stover and corn cob were identified. In general, they inhibited cell growth, lactate dehydrogenase, and lactic acid production but with less or no adverse effect on alcohol dehydrogenase and ethanol production in batch fermentation by Rhizopus oryzae. Furfural and 5-hydroxymethyl furfural (HMF) were highly toxic at 0.5-1 g L(-1), while formic and acetic acids at less than 4 g L(-1) and levulinic acid at 10 g L(-1) were not toxic. Among the phenolic compounds at 1 g L(-1), trans-cinnamic acid and syringaldehyde had the highest toxicity while syringic, ferulic and p-coumaric acids were not toxic. Although these inhibitors were present at concentrations much lower than their separately identified toxic levels, lactic acid fermentation with the hydrolysates showed much inferior performance compared to the control without inhibitor, suggesting synergistic or compounded effects of the lignocellulose-degraded compounds on inhibiting lactic acid fermentation.

Assessing adsorption of polycyclic aromatic hydrocarbons on Rhizopus oryzae cell wall components with water-methanol cosolvent model

The contribution of different fungal cell wall components in adsorption of polycyclic aromatic hydrocarbons (PAHs) is still unclear. We isolated Rhizopus oryzae cell walls components with sequential extraction, characterized functional groups with NEXAFS spectra, and determined partition coefficients of PAHs on cell walls and cell wall components with cosolvent model. Spectra of NEXAFS indicated that isolated cell walls components were featured with peaks at ~532.7 and ~534.5eV energy. The lipid cosolvent partition coefficients were approximately one order of magnitude higher than the corresponding carbohydrate cosolvent partition coefficients. The partition coefficients for four tested carbohydrates varied at approximate 0.5 logarithmic units. Partition coefficients between biosorbents and water calculated based cosolvent models ranged from 0.8 to 4.2. The present study proved the importance of fungal cell wall components in adsorption of PAHs, and consequently the role of fungi in PAHs bioremediation.

Activation of glycerol metabolic pathway by evolutionary engineering of Rhizopus oryzae to strengthen the fumaric acid biosynthesis from crude glycerol

Rhizopus oryzae is strictly inhibited by biodiesel-based by-product crude glycerol, which results in low fumaric acid production. In this study, evolutionary engineering was employed to activate the glycerol utilization pathway for fumaric acid production. An evolved strain G80 was selected, which could tolerate and utilize high concentrations of crude glycerol to produce 14.9g/L fumaric acid with a yield of 0.248g/g glycerol. Key enzymes activity analysis revealed that the evolved strain displayed a significant upregulation in glycerol dissimilation, pyruvate consumption and reductive tricarboxylic acid pathways, compared with the parent strain. Subsequently, intracellular metabolic profiling analysis showed that amino acid biosynthesis, tricarboxylic acid cycle, fatty acid and stress response metabolites accounted for metabolic difference between two strains. Moreover, a glycerol fed-batch strategy was optimized to obtain the highest fumaric acid production of 25.5g/L, significantly increased by 20.9-fold than that of the parent strain of 1.2g/L.

High production of fumaric acid from xylose by newly selected strain Rhizopus arrhizus RH 7-13-9#

Fumaric acid, as an important material for polymerization, is highly expected to be produced by fermentation of lignocellulosic biomass which is composed of cellulose, hemicellulose and lignin. Xylose as the main component of hemicellulose cannot be efficiently utilized by most of the common fermentation. In this study, a new strain Rhizopus arrhizus RH 7-13-9# was selected from the R. arrhizus RH 7-13 through a novel convenient and efficient selection method. Efficient production of fumaric acid (45.31 g/L) from xylose was achieved by the new strain, and the volumetric productivity was still 0.472 g/L h. Moreover, the conversion of xylose reached 73% which is close to the theoretic yield (77%). The production of fumaric acid was increased approximate by 172%, compared with the initial strain counterpart. These results indicated that xylose, as the main component of hemicellulose, has a promising application for the production of fumaric acid on an industrial-scale.

A model for growth of a single fungal hypha based on well-mixed tanks in series: simulation of nutrient and vesicle transport in aerial reproductive hyphae

Current models that describe the extension of fungal hyphae and development of a mycelium either do not describe the role of vesicles in hyphal extension or do not correctly describe the experimentally observed profile for distribution of vesicles along the hypha. The present work uses the n-tanks-in-series approach to develop a model for hyphal extension that describes the intracellular transport of nutrient to a sub-apical zone where vesicles are formed and then transported to the tip, where tip extension occurs. The model was calibrated using experimental data from the literature for the extension of reproductive aerial hyphae of three different fungi, and was able to describe different profiles involving acceleration and deceleration of the extension rate. A sensitivity analysis showed that the supply of nutrient to the sub-apical vesicle-producing zone is a key factor influencing the rate of extension of the hypha. Although this model was used to describe the extension of a single reproductive aerial hypha, the use of the n-tanks-in-series approach to representing the hypha means that the model has the flexibility to be extended to describe the growth of other types of hyphae and the branching of hyphae to form a complete mycelium.

[Effects of pellet characteristics on L-lactic acid fermentation by Rhizopus oryzae]

OBJECTIVE

Effects of pellet morphology, diameter, density, and interior structure on L-lactic acid fermentation by Rhizopus oryzae were characterized for different inoculum sizes and concentrations of peptone and CaCO3.

METHODS

Different initial spore concentrations were inoculated in the preculture medium with different peptone and CaCO3 concentrations, and cultivated at 30 degrees C for 36 h. Representative pellets were chosen for interior structure analysis and L-lactic acid production.

RESULTS

Inoculum size was the most important factor determining pellet formation and diameter. Peptone concentration had the greatest effect on pellet density. L-lactic acid production depended heavily on pellet density but not on pellet diameter. Low-density pellets formed easily under conditions of low peptone concentration and often had a relatively hollow structure. This structure greatly decreased production. The production of L-lactic acid increased until the density reached a certain level (50 - 60 kg/m3) , which the compact part distributed homogeneously in the thick outer layer of the pellet, and loose in the central layer. Homogeneously structured, denser pellets limited mass transfer. CaCO, concentration only had a slight influence on pellet diameter and density.

CONCLUSION

This work provides the insight into pellet structure and its relationship with productivity.

A metabolic-based approach to improve xylose utilization for fumaric acid production from acid pretreated wheat bran by Rhizopus oryzae

In this work, wheat bran (WB) was utilized as feedstock to synthesize fumaric acid by Rhizopus oryzae. Firstly, the pretreatment process of WB by dilute sulfuric acid hydrolysis undertaken at 100°C for 30min offered the best performance for fumaric acid production. Subsequently, through optimizing the seed culture medium, a suitable morphology (0.55mm pellets diameter) of R. oryzae was obtained. Furthermore, a metabolic-based approach was developed to profile the differences of intracellular metabolites concentration of R. oryzae between xylose (the abundant sugar in wheat bran hydrolysate (WBH)) and glucose metabolism. The xylitol, sedoheptulose 7-phosphate, ribulose 5-phosphate, glucose 6-phosphate, proline and serine were responsible for fumaric acid biosynthesis limitation in xylose fermentation. Consequently, regulation strategies were proposed, leading to a 149% increase in titer (up to 15.4g/L). Finally, by combinatorial regulation strategies the highest production was 20.2g/L from WBH, 477% higher than that of initial medium.

In vitro antimalarial studies of novel artemisinin biotransformed products and its derivatives

Biotransformation of antimalarial drug artemisinin by fungi Rhizopus stolonifer afforded three sesquiterpenoid derivatives. The transformed products were 1α-hydroxyartemisinin (3), 3.0%, a new compound, 10β-hydroxyartemisinin, 54.5% (4) and deoxyartemisinin (2) in 9% yield. The fungus expressed high-metabolism activity (66.5%). The chemical structures of the compounds were elucidated by 1D, 2D NMR spectrometry and mass spectral data. The major compound 10β-hydroxyartemisinin (4) was chemically converted to five new derivatives 5-9. All the compounds 3-9 were subjected for in vitro anti-malarial activity. 10β-Hydroxy-12β-arteether (8), IC50 at 18.29nM was found to be 10 times better active than its precursor 4 (184.56nM) and equipotent antimalarial with natural drug artemisinin whereas the α-derivative 9 is 3 times better than 4 under in vitro conditions. Therefore, the major biotransformation product 4 can be exploited for further modification into new clinically potent molecules. The results show the versatility of microbial-catalyzed biotransformations leading to the introduction of a hydroxyl group at tertiary position in artemisinin in derivative (3).

Novel fungal consortium for bioremediation of metals and dyes from mixed waste stream

The present study is targeted towards development of a three member fungal consortium for effective removal of metals [Cr(6+) and Cu(2+)] and dyes [AB and PO] from mixed waste streams. Initial studies using individual fungal strain showed that Aspergillus lentulus was best for Cu(2+) and AB removal, Aspergillus terreus for Cr(6+) removal whereas, Rhizopus oryzae was best for PO removal. Based on the complementary pollutant affinities and positive interactions, a consortium comprising all three strains was developed. Consortium removed 100% Cr(6+) and 81.60% Cu(2+) from metal mixture which was significantly higher than that achieved individually by A. lentulus (Cr(6+): 83.11%; Cu(2+): 67.32%), A. terreus (Cr(6+): 95.57%; Cu(2+): 65.77%) or R. oryzae (Cr(6+): 25.34%; Cu(2+): 30.20%). Further, 98.0% AB and 100.0% PO was removed after 48 h by the consortia. Unlike individual strains, consortium's performance was unaltered irrespective of the complexity of metal-dye mixtures, thereby establishing its superiority.