Gene Transfer Between Different Trichoderma Species and Aspergillus Niger Through Intergeneric Protoplast Fusion to Convert Ground Rice Straw to Citric Acid and Cellulases

Strategies for the Development of Industrial Fungal Producing Strains

The use of microorganisms in industry has enabled the (over)production of various compounds (e.g., primary and secondary metabolites, proteins and enzymes) that are relevant for the production of antibiotics, food, beverages, cosmetics, chemicals and biofuels, among others. Industrial strains are commonly obtained by conventional (non-GMO) strain improvement strategies and random screening and selection. However, recombinant DNA technology has made it possible to improve microbial strains by adding, deleting or modifying specific genes. Techniques such as genetic engineering and genome editing are contributing to the development of industrial production strains. Nevertheless, there is still significant room for further strain improvement. In this review, we will focus on classical and recent methods, tools and technologies used for the development of fungal production strains with the potential to be applied at an industrial scale. Additionally, the use of functional genomics, transcriptomics, proteomics and metabolomics together with the implementation of genetic manipulation techniques and expression tools will be discussed.

Purification, characterization, and anticancer and antioxidant activities of L-glutaminase from Aspergillus versicolor Faesay4

L-Glutaminase is an amidohydrolase which can act as a vital chemotherapeutic agent against various malignancies. In the present work, L-glutaminase productivity from Aspergillus versicolor Faesay4 was significantly increased by 7.72-fold (from 12.33 ± 0.47 to 95.15 ± 0.89 U/mL) by optimizing submerged fermentation parameters in Czapek's Dox (CZD) medium including an incubation period from 3 (12.33 ± 0.47 U/mL) to 6 days (23.36 ± 0.58 U/mL), an incubation temperature from 30 °C (23.36 ± 0.49 U/mL) to 25 °C (31.08 ± 0.60 U/mL), initial pH from pH 5.0 (8.49 ± 0.21 U/mL)  to pH 7.0 (32.18 ± 0.57 U/mL), replacement of glucose (30.19 ± 0.52 U/mL) by sucrose (48.97 ± 0.67 U/mL) as the carbon source at a concentration of 2.0% (w/v), increasing glutamine concentration as the nitrogen source from 1.0% (w/v, 48.54 ± 0.48 U/mL) to 1.5% (w/v, 63.01 ± 0.60 U/mL), and addition of a mixture of KH₂PO₄ and NaCl (0.5% w/v for both) to SZD as the metal supplementation (95.15 ± 0.89 U/mL). Faesay4 L-glutaminase was purified to yield total activity 13,160 ± 22.76 (U), specific activity 398.79 ± 9.81 (U/mg of protein), and purification fold 2.1 ± 3.18 with final enzyme recovery 57.22 ± 2.17%. The pure enzyme showed a molecular weight of 61.80 kDa, and it was stable and retained 100.0% of its activity at a temperature ranged from 10 to 40 °C and pH 7.0. In our trials, to increase the enzyme activity by optimizing the assay conditions (which were temperature 60 °C, pH 7.0, substrate glutamine, substrate concentration 1.0%, and reaction time 60 min), the enzyme activity increased by 358.8% after changing the assay temperature from 60 to 30 °C and then increased by 138% after decreasing the reaction time from 60 to 40 min. However, both pH 7.0 and glutamine as the substrate remain the best assay parameters for the L-glutaminase activity. When the glutamine in the assay as the reaction substrate was replaced by asparagine, lysine, proline, methionine, cysteine, glycine, valine, phenylalanine, L-alanine, aspartic acid, tyrosine, and serine, the enzyme lost 23.86%, 29.0%, 31.0%, 48.3%, 50.0%, 73.6%, 74.51%, 80.42%, 82.5%, 83.43%, 88.36%, and 89.78% of its activity with glutamine, respectively. Furthermore, Mn²⁺, K⁺, Na⁺, and Fe³⁺ were enzymatic activators that increased the L-glutaminase activity by 25.0%, 18.05%, 10.97%, and 8.0%, respectively. Faesay4 L-glutaminase was characterized as a serine protease enzyme as a result of complete inhibition by all serine protease inhibitors (PMSF, benzamidine, and TLCK). Purified L-glutaminase isolated from Aspergillus versicolor Faesay4 showed potent DPPH scavenging activities with IC₅₀ = 50 μg/mL and anticancer activities against human liver (HepG-2), colon (HCT-116), breast (MCF-7), lung (A-549), and cervical (Hela) cancer cell lines with IC₅₀ 39.61, 12.8, 6.18, 11.48, and 7.25 μg/mL, respectively.

Improvement of Ethanol Tolerance by Inactive Protoplast Fusion in Saccharomyces cerevisiae

Saccharomyces cerevisiae is a typical fermentation yeast in beer production. Improving ethanol tolerance of S. cerevisiae will increase fermentation efficiency, thereby reducing capital costs. Here, we found that S. cerevisiae strain L exhibited a higher ethanol tolerance (14%, v/v) than the fermentative strain Q (10%, v/v). In order to enhance the strain Q ethanol tolerance but preserve its fermentation property, protoplast fusion was performed with haploids from strain Q and L. The fusant Q/L-f2 with 14% ethanol tolerance was obtained. Meanwhile, the fermentation properties (flocculability, SO2 production, α-N assimilation rate, GSH production, etc.) of Q/L-f2 were similar to those of strain Q. Therefore, our works established a series of high ethanol-tolerant strains in beer production. Moreover, this demonstration of inactivated protoplast fusion in industrial S. cerevisiae strain opens many doors for yeast-based biotechnological applications.

Molecular heterozygosity and genetic exploitations of Trichoderma inter-fusants enhancing tolerance to fungicides and mycoparasitism against Sclerotium rolfsii Sacc

Protoplast fusion is an imperative tool to develop Trichoderma inter-fusants having desire traits through genetic manipulation. Study designed to develop diverse Trichoderma fusants for fungicide tolerance (Mancozeb, Thiram, Tebuconazole, and Carbendazim) and enhanced mycoparasitic activity against Sclerotium rolfsii sacc. The mycoparasitic T. virens NBAII Tvs12 and fungicide tolerant T. koningii MTCC 796 were utilized for protoplast fusion. The derived inter-fusants were subjected to diploidization using d-camphor in minimal media followed by successive three sub culturing onto potato dextrose agar to obtain 36 stable fusants. The stable fusants were employed for conidial size, fungicide tolerance, mycoparasitism, gene specific SSR amplification and molecular heterozygosity analysis. The results explained that 22 homozygous mutants illustrated characteristic of either one parental strain and 14 heterozygous recombinants depicted traits of both parental strains. The antagonistic activity of fusants against S. rolfsii depicted highest growth inhibition (87.91%) by potent inter-fusant (Fu 21) with improved fungicide tolerance capacity. The molecular study revealed highest observed heterozygocity (0.544), coefficient of gene differentiation (0.526) and gene flow (0.387) by Fu 21 indicating better genetic exploitation of parental strains into that fusant with good genetic purity. Principal coordinate analysis of fusants and parental strains exhibited 65.07% total variation and confirmed the scattering pattern matched with UPGMA clustering pattern. The stable heterozygous Fu 21 derived from inter-fusion between Tvs 12 and MTCC 796 might be useful to practice eco-friendly bioformulation tolerance to fungicides for effective integrated stem rot disease management in groundnut.

Phylogenetic Analysis and Biological Evaluation of Marine Endophytic Fungi Derived from Red Sea Sponge Hyrtios erectus

Forty-four endophytic fungal isolates obtained from marine sponge, Hyrtios erectus, were evaluated and screened for their hydrolase activities. Most of the isolates were found to be prolific producers of hydrolytic enzymes. Only 11 isolates exhibited maximum cellular contents of lipids, rhamnolipids, and protein in the fungal isolates under the isolation numbers MERVA5, MERVA22, MERVA25, MERVA29, MERVA32, MERVA34, MERV36, MERVA39, MERVA42, MERVA43, and MERVA44. These isolate extracts exhibit the highest reducing activities against carbohydrate-metabolizing enzymes including α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase. Consequently, based on morphological and cultural criteria, as well as sequence information and phylogenetic analysis, these isolates could be identified and designated as Penicillium brevicombactum MERVA5, Arthrinium arundinis MERVA22, Diaporthe rudis MERVA25, Aspergillus versicolor MERVA29, Auxarthron alboluteum MERVA32, Dothiorella sarmentorum MERVA34, Lophiostoma sp. MERVA36, Fusarium oxysporum MERVA39, Penicillium chrysogenum MERVA42, Penicillium polonicum MERVA43, and Trichoderma harzianum MERVA44. The endophytic fungal species, D. rudis MERVA25, P. polonicum MERVA43, Lophiostoma sp. MERVA36, A. alboluteum MERVA32, T. harzianum MERVA44, F. oxysporum MERVA39, A. versicolor MERVA29, and P. chrysogenum MERVA42 extracts, showed significant hepatitis C virus (HCV) inhibition. Moreover, D. sarmentorum MERVA34, P. polonicum MERVA43, and T. harzianum MERVA44 extracts have the highest antitumor activity against human hepatocellular carcinoma cells (HepG2).

Construction of Potent Recombinant Strain Through Intergeneric Protoplast Fusion in Endophytic Fungi for Anticancerous Enzymes Production Using Rice Straw

Among all fungal endophytes isolates derived from different ethno-medical plants, the hyper-yield L-asparaginase and L-glutaminase wild strains Trichoderma sp. Gen 9 and Cladosporium sp. Gen 20 using rice straw under solid-state fermentation (SSF) were selected. The selected strains were used as parents for the intergeneric protoplast fusion program to construct recombinant strain for prompt improvement production of these enzymes in one recombinant strain. Among 21 fusants obtained, the recombinant strain AYA 20-1, with 2.11-fold and 2.58-fold increase in L-asparaginase and L-glutaminase activities more than the parental isolates Trichoderma sp. Gen 9 and Cladosporium sp. Gen 20, respectively, was achieved using rice straw under SSF. Both therapeutic enzymes L-asparaginase and L-glutaminase were purified and characterized from the culture supernatant of the recombinant AYA 20-1 strain with molecular weights of 50.6 and 83.2 kDa, respectively. Both enzymes were not metalloenzymes. Whereas thiol group blocking reagents such as p-chloromercurybenzoate and iodoacetamide totally inhibited L-asparaginase activity, which refer to sulfhydryl groups and cysteine residues involved in its catalytic activity, they have no effect toward L-glutaminase activity. Interestingly, potent anticancer, antioxidant, and antimicrobial activities were detected for both enzymes.

Microbial-processing of fruit and vegetable wastes for production of vital enzymes and organic acids: Biotechnology and scopes

Wastes generated from fruits and vegetables are organic in nature and contribute a major share in soil and water pollution. Also, green house gas emission caused by fruit and vegetable wastes (FVWs) is a matter of serious environmental concern. This review addresses the developments over the last one decade on microbial processing technologies for production of enzymes and organic acids from FVWs. The advances in genetic engineering for improvement of microbial strains in order to enhance the production of the value added bio-products as well as the concept of zero-waste economy have been briefly discussed.

Molecular identification using ITS sequences and genome shuffling to improve 2-deoxyglucose tolerance and xylanase activity of marine-derived fungus, Aspergillus sp. NRCF5

During the screening of xylanolytic enzyme from marine-derived fungi isolated from the inner tissue of Egyptian soft coral Rhytisma sp., one strain, NRCF5, exhibited high enzyme activity with 0.1 % (w/v) antimetabolite 2-deoxyglucose (2DG) tolerance. This fungal strain was identified as Aspergillus sp. NRCF5 based on its morphological characteristics and internal transcribed spacer (ITS) sequences. The ITS region of hyperactive xylanolytic strain (NRCF5) was amplified, sequenced, and submitted to GenBank (accession no. JQ277356). To apply the fundamental principles of genome shuffling in breeding of xylanase-producing fungi, marine-derived fungus Aspergillus sp. NRCF5 was used as starting strain in this work and applied for induction of genetic variability using different combinations and doses of mutagens. Five mutants with high xylanase activity and 0.25 % (w/v) antimetabolite 2DG tolerance were obtained from the populations generated by the mutation of combination between ultraviolet irradiation (UV, 5 min) and N-methyl-N-nitro-N-nitrosoguanidine (NTG, 100 μg/ml) for 30 (UNA) and 60 (UNB)min as well as NTG (100 μg/ml) and ethidium bromide (250 μg/ml) for 30 (NEA) and 60 (NEB)min. Then, they were subjected for recursive protoplast fusion. Seven hereditarily stable recombinants with high xylanase activity and 1.0 % (w/v) 2DG tolerance were obtained by four rounds of genome shuffling. Among them, a high xylanase-producing recombinant, R4/31, was obtained, which produced 427.5 U/ml xylanase. This value is 6.13-fold higher than that of the starting strain NRCF5 and 2.48-fold higher than that of the parent strain (mutant NEA51). The subculture experiments indicated that the high producer of marine Aspergillus sp. R4/31 fusant was stable.

Cellulase production from agricultural residues by recombinant fusant strain of a fungal endophyte of the marine sponge Latrunculia corticata for production of ethanol

Several fungal endophytes of the Egyptian marine sponge Latrunculia corticata were isolated, including strains Trichoderma sp. Merv6, Penicillium sp. Merv2 and Aspergillus sp. Merv70. These fungi exhibited high cellulase activity using different lignocellulosic substrates in solid state fermentations (SSF). By applying mutagenesis and intergeneric protoplast fusion, we have obtained a recombinant strain (Tahrir-25) that overproduced cellulases (exo-β-1,4-glucanase, endo-β-1,4-glucanase and β-1,4-glucosidase) that facilitated complete cellulolysis of agricultural residues. The process parameters for cellulase production by strain Tahrir-25 were optimized in SSF. The highest cellulase recovery from fermentation slurries was achieved with 0.2% Tween 80 as leaching agent. Enzyme production was optimized under the following conditions: initial moisture content of 60% (v/w), inoculum size of 10(6) spores ml(-1), average substrate particle size of 1.0 mm, mixture of sugarcane bagasse and corncob (2:1) as the carbon source supplemented with carboxymethyl cellulose (CMC) and corn steep solids, fermentation time of 7 days, medium pH of 5.5 at 30°C. These optimized conditions yielded 450, 191, and 225 units/gram dry substrate (U gds(-1)) of carboxylmethyl cellulase, filter-paperase (FPase), and β-glucosidase, respectively. Subsequent fermentation by the yeast, Saccharomyces cerevisiae NRC2, using lignocellulose hydrolysates obtained from the optimized cellulase process produced the highest amount of ethanol (58 g l(-1)). This study has revealed the potential of exploiting marine fungi for cost-effective production of cellulases for second generation bioethanol processes.

Identification of potential marker genes for Trichoderma harzianum strains with high antagonistic potential against Rhizoctonia solani by a rapid subtraction hybridization approach

A rapid subtraction hybridization approach was used to isolate genes differentially expressed during mycelial contact between Trichoderma harzianum (Hypocrea lixii) and Rhizoctonia solani, and could serve as marker genes for selection of superior biocontrol strains. Putatively positive clones were evaluated by transcription analysis during mycelial contact with R. solani versus growth on glucose, and for their differential transcription between two strains with either strong or poor biocontrol capability before, at, and after contact with R. solani. Besides four clones, which had similarity to putative but as yet uncharacterized proteins, they comprised ribosomal proteins, proteins involved in transcriptional switch and regulation, amino acid and energy catabolism, multidrug resistance, and degradation of proteins and glucans. Transcription of three clones was evaluated in five T. harzianum strains under confrontation conditions with R. solani. Two clones-acetyl-xylane esterase AXE1 and endoglucanase Cel61b-showed significant upregulation during in vivo confrontation of a T. harzianum strain that successively demonstrated a very high antagonistic capability towards R. solani, while expression was progressively lower in a series of T. harzianum strains with intermediate to poor antagonistic activity. These clones are promising candidates for use as markers in the screening of improved T. harzianum biocontrol strains.

Polyploid formation between Aspergillus niger and Trichoderma viride for enhanced citric acid production from cellulose

The first-stage heterokaryons, obtaining from intergeneric protoplast fusion between Aspergillus niger (Y-b) and Trichoderma viride (M5S51), showed slow growth and mixed morphologies on minimal medium. The fusants were classified into heterokaryon and prototrophic haploid, showing the morphology as that of A. niger. The heterokaryon strains formed conidia with the same nutritional requirements as those of the original auxotrophic mutant strains. After several subcultivations on minimal medium containing d-camphor, some heterokaryon strains formed larger two to seven nuclei/conidium as compared to one nucleus/conidium of the auxotrophic mutant and prototrophic strains, indicating that the new hybrids were generated. Interestingly, three fusant strains AT 11-2-3, AT 11-2-10, and AT 11-2-14 produce 19.2, 6.1, and 10.5 g/l citric acid, respectively, in semisolid culture containing cellulose, whereas A. niger Yang no. 2 could not use carboxymethyl cellulose as the sole carbon source for citric acid production. In addition, the average maximum beta-glucosidase and carboxymethylcellulase productions from AT 11-2-3, AT 11-2-10, and AT 11-2-14 were about 16- and 4-folds higher than those of A. niger, respectively.