Presidential address: Fungi without coats — protoplasts as tools for mycological research

Enhancement of cellulolytic enzyme production from intrageneric protoplast fusion of Aspergillus species and evaluating the hydrolysate scavenging activity

BACKGROUND

Lignocellulosic biomass provides a great starting point for the production of energy, chemicals, and fuels. The major component of lignocellulosic biomass is cellulose, the employment of highly effective enzymatic cocktails, which can be produced by a variety of microorganisms including species of the genus Aspergillus, is necessary for its utilization in a more productive manner. In this regard, molecular biology techniques should be utilized to promote the economics of enzyme production, whereas strategies like protoplast fusion could be employed to improve the efficacy of the hydrolytic process.

RESULTS

The current study focuses on cellulase production in Aspergillus species using intrageneric protoplast fusion, statistical optimization of growth parameters, and determination of antioxidant activity of fermentation hydrolysate. Protoplast fusion was conducted between A. flavus X A. terreus (PFFT), A. nidulans X A. tamarii (PFNT) and A. oryzae X A. tubingensis (PFOT), and the resultant fusant PFNT revealed higher activity level compared with the other fusants. Thus, this study aimed to optimize lignocellulosic wastes-based medium for cellulase production by Aspergillus spp. fusant (PFNT) and studying the antioxidant effect of fermentation hydrolysate. The experimental strategy Plackett-Burman (PBD) was used to assess how culture conditions affected cellulase output, the best level of the three major variables namely, SCB, pH, and incubation temperature were then determined using Box-Behnken design (BBD). Consequently, by utilizing an optimized medium instead of a basal medium, cellulase activity increased from 3.11 U/ml to 7.689 U/ml CMCase. The following medium composition was thought to be ideal based on this optimization: sugarcane bagasse (SCB), 6.82 gm; wheat bran (WB), 4; Moisture, 80%; pH, 4; inoculum size, (3 × 106 spores/ml); and incubation Temp. 31.8 °C for 4 days and the fermentation hydrolysate has 28.13% scavenging activities.

CONCLUSION

The results obtained in this study demonstrated the significant activity of the selected fusant and the higher sugar yield from cellulose hydrolysis over its parental strains, suggesting the possibility of enhancing cellulase activity by protoplast fusion using an experimental strategy and the fermentation hydrolysate showed antioxidant activity.

Fungal evolution: cellular, genomic and metabolic complexity

The question of how phenotypic and genomic complexity are inter-related and how they are shaped through evolution is a central question in biology that historically has been approached from the perspective of animals and plants. In recent years, however, fungi have emerged as a promising alternative system to address such questions. Key to their ecological success, fungi present a broad and diverse range of phenotypic traits. Fungal cells can adopt many different shapes, often within a single species, providing them with great adaptive potential. Fungal cellular organizations span from unicellular forms to complex, macroscopic multicellularity, with multiple transitions to higher or lower levels of cellular complexity occurring throughout the evolutionary history of fungi. Similarly, fungal genomes are very diverse in their architecture. Deep changes in genome organization can occur very quickly, and these phenomena are known to mediate rapid adaptations to environmental changes. Finally, the biochemical complexity of fungi is huge, particularly with regard to their secondary metabolites, chemical products that mediate many aspects of fungal biology, including ecological interactions. Herein, we explore how the interplay of these cellular, genomic and metabolic traits mediates the emergence of complex phenotypes, and how this complexity is shaped throughout the evolutionary history of Fungi.

Interspecific hybridization between cultivated morels Morchella importuna and Morchella sextelata by PEG-induced double inactivated protoplast fusion

The commercial production of Morchella mushrooms calls for urgent breeding of excellent varieties or strains with appropriate tools, such as protoplast fusion. However, the protoplast fusion in morels has not been studied. In this paper, interspecific hybridization between cultivated morels of M. importuna and M. sextelata by PEG-induced protoplast fusion was conducted. Apart from functional complementation of double inactivated protoplasts, the fusants were characterized by cultural and cultivated characters and molecular markers of random amplified polymorphic DNA (RAPD). The results suggested that the hybrids and their parents showed significant difference in their inoculum recovery time, mycelial growth rate, yield of cultivation and total amino acid content of ascocarps. Moreover, positive barrage reactions were observed between parental strains as well as between each parent and a hybrid line. A dendrogram created on the basis of RAPD fingerprints exhibited three major clusters, in which morel hybrids showed intra-cluster variations, M. sextelata #6 formed an out group, while M. importuna #4 was phylogenetically closer to morel hybrids. All the results demonstrated that real fusants were obtained in our study. Protoplast fusion may provide an ideal alternative for new strain selection, and thus will promote the healthy development of morel industry.

Microalgae protoplasts isolation and fusion for biotechnology research

Protoplasts are microbial or vegetable cells lacking a cell wall. These can be obtained from microalgae by an enzymatic hydrolysis process in the presence of an osmotic stabilizer. In general, protoplasts are experimentally useful in physiological, geneticand bio-chemical studies, so their acquisition and fusion will continue to be an active research area in modern biotechnology. The fusion of protoplasts in microalgae constitutes a tool for strain improvement because it allows both intra and interspecific genetic recombina-tion, resulting in organisms with new or improved characteristics of industrial interest. In this review we briefly describe themethod-ology for obtaining protoplasts, as well as fusion methods and the main applications of microalgal platforms.

A new variant produced by Rhizoctonia solani AG1-IC isolate CH-1 with a new type of nuclei

BACKGROUND

Isolate CH-1 of Rhizoctonia solani Kühn was commonly used in our studies of the pathogenicity and genetics of this pathogen. During the preparation of homokaryons through protoplast regeneration and tuft formation, a defective homokaryon was detected and a new variant was obtained.

RESULTS

When tuft formation was used to identify the karyotic nature of single protoplast regenerants (SPRs) of Rhizoctonia solani AG1-IC isolate CH-1, one homokaryon type designated as A type and the parental heterokaryon designated as AB type were obtained. The homokaryon B type was not found. Various approaches were used to obtain SPRs, including from fast or slow growing protoplast regenerants, and from regenerants of protoplasts released from mycelia grown in different nutrient broths or at different temperatures. Without exception, all these SPRs were either homokaryon A or heterokaryon AB. Moreover, the SPRs obtained from different generations of SPRs, and from different generations of SPRs treated with lytic enzymes 3 to 4 times also were invariably either homokaryon A or heterokaryon AB. When single hyphal isolates were obtained from the tuft resulting from the pairing between homokaryon A and heterokaryon AB, only the heterokaryon and a variant were obtained. The variant did not form tuft when paired with parental heterokaryon AB or homokaryon A. Its protoplast regenerants gave rise to heterokaryon AB, homokaryon A and the variant, indicating that it is a new kind of heterokaryon.

CONCLUSION

Inability to obtain homokaryon B despite numerous attempts suggests that the B type nuclei are probably defective and are dependent on A type nuclei for their multiplication. This is the first report of a heterokaryotic R. solani strain carrying a defective type of nuclei. A new variant which is a new kind of heterokaryon was obtained from the tuft resulting from the paring between the homokaryon A and the parental heterokaryon AB.

Intraspecific hybridization between Coprinus cinereus and Schizophyllum commune by PEG-induced protoplast fusion and electrofusion

Two irreversible inhibitors, iodoacetamide and diethylpyrocarbonate, were used to select intraspecific fusion products of two mushroom species, Coprinus cinereus and Schizophyllum commune. Iodoacetamide was the more suitable inhibitor because it gave a low breakage frequency and low survival rate of the cells in the inactivation experiments. Fusion-induced by polyethylene glycol and electro-fusion were compared and, under optimal conditions, gave fusion frequencies of 16.7% to 50.0% and 6.9% to 8.4%, respectively. All fusion progeny were heterokaryons (dikaryons) and had clamp connections. There were no differences in the morphology and fruiting ability of the fusion progeny and those of the heterokaryons generated from mating.

Chitinases: in agriculture and human healthcare

Biological control of phytopathogenic fungi and insects continues to inspire the research and development of environmentally friendly bioactive alternatives. Potentially lytic enzymes, chitinases can act as a biocontrol agent against agriculturally important fungi and insects. The cell wall in fungi and protective covers, i.e. cuticle in insects shares a key structural polymer, chitin, a β-1,4-linked N-acetylglucosamine polymer. Therefore, it is advantageous to develop a common biocontrol agent against both of these groups. As chitin is absent in plants and mammals, targeting its metabolism will signify an eco-friendly strategy for the control of agriculturally important fungi and insects but is innocuous to mammals, plants, beneficial insects and other organisms. In addition, development of chitinase transgenic plant varieties probably holds the most promising method for augmenting agricultural crop protection and productivity, when properly integrated into traditional systems. Recently, human proteins with chitinase activity and chitinase-like proteins were identified and established as biomarkers for human diseases. This review covers the recent advances of chitinases as a biocontrol agent and its various applications including preparation of medically important chitooligosaccharides, bioconversion of chitin as well as in implementing chitinases as diagnostic and prognostic markers for numerous diseases and the prospect of their future utilization.

Regeneration and molecular characterization of an intergeneric hybrid between Graphium putredinis and Trichoderma harzianum by protoplasmic fusion

The fungal strains Graphium putredinis and Trichoderma harzianum were selected as parents for fusant development. Protoplasts were isolated using the combination of lysing enzymes Novozym 234 and cellulase with 0.6M KCl as osmotic stabilizer. The optimum conditions for release of viable protoplasts from the fungal mycelium viz. age of the mycelium, lytic enzymes, osmotic stabilizers, pH, incubation period and regeneration medium were determined. Intergeneric protoplast fusion was carried out using 50% polyethylene glycol with calcium chloride (CaCl(2)) and glycine buffer and the conditions for effective protoplast fusion, viz. fusogen, osmotic stabilizer, pH, incubation period and regeneration medium were optimized. At optimum conditions, the regeneration frequency of the fused protoplasts on potato dextrose agar (PDA) medium and fusion frequency were calculated. The regeneration frequency on non-selective (PDA) and selective media (PDA amended with starch) was determined for the parental and fusant strains in which, fusant showed a higher rate of regeneration. Fusant formation was confirmed by morphological markers (colony morphology and spore size and shape) and genetical markers like, mycelial protein pattern, restriction digestion pattern and random amplified polymorphic DNA (RAPD) analysis. The efficiency of these parental strains and their intergeneric fusant in the production of hydrolytic enzymes - amylases (treatment plant for sago factory effluent), cellulases (bioethanol), xylanases (bleaching agents for waste paper pulp) and proteases (additives in commercial detergents) - have probable applications in various industrial processes.

Factors affecting protoplast formation by Rhizoctonia solani

Novozym 234 was the most frequently used enzyme for production of Rhizoctonia solani protoplasts. Since manufacture of this enzyme was discontinued in the late 1990s, a new procedure was developed by testing lytic enzymes from Sigma and by examining factors affecting protoplast formation. The combination of 20 mg/mL Driselase and 10mg/mL lysing enzyme was effective in releasing protoplasts from R. solani. The optimal condition for enzyme treatment of mycelium was incubation at 37 degrees C for 15 min followed by 34 degrees C for 105 min. The amount of protoplasts produced was positively correlated with growth rate and negatively correlated with mycelial density. Under favorable conditions, R. solani mycelia released 1.68 x 10(6) protoplasts/mL that is comparable with that produced with Novozym 234. Among various media tested, the best solid medium for protoplast regeneration was 1% V-8 juice agar, while the best liquid medium was 10% potato dextrose broth.

Isolation, Regeneration and PEG-Induced Fusion of Protoplasts of Pleurotus pulmonarius and Pleurotus florida

Inter-specific hybridization between Pleurotus pulmonarius and P. florida was attempted through PEG-induced protoplast fusion to select a fusant. The protocol for protoplast release, regeneration and fusion in these two Pleurotus species was standardized using the variables controlling the process. The mixture of mycolytic enzymes, i.e. commercial cellulase, crude chitinase and pectinase, KCl (0.6 M) as osmotic stabilizer, pH 6 of the phosphate buffer and an incubation time of 3 hours resulted in the maximum release of protoplasts from 3-day-old mycelia of P. florida (5.3~5.75 × 10(7) protoplasts/g) and P. pulmonarius (5.6~6 × 10(7) protoplasts/g). The isolated protoplasts of P. florida regenerated mycelium with 3.3% regeneration efficiency while P. pulmonarius showed 4.1% efficiency of regeneration. Polyethyleneglycol (PEG) - induced fusion of protoplasts of these two species resulted in 0.28% fusion frequency. The fusant produced fruiting bodies on paddy straw but required a lower temperature of crop running (24 ± 2℃) than its parents which could fruit at 28 ± 2℃. The stable fusant strain was selected by testing for the selected biochemical markers i.e. Carbendazim tolerance and utilization of the lignin degradation product, vanillin.

Isolation and regeneration of protoplasts from the yeast and mycelial form of the dimorphic zygomycete Benjaminiella poitrasii: role of chitin metabolism for morphogenesis during regeneration

Experimental parameters for isolation and regeneration of protoplasts from the mycelial and yeast form cells of the dimorphic zygomycete Benjamininiella poitrasii are reported. Using a chitosanase containing preparation from Streptomyces sp. MCl we obtained protoplasts after 5 h incubation with a yield of 2+/-0.3 x 10(6) ml(-1) and 3+/-0.4 x 10(7) ml(-1) for the mycelial and yeast form, respectively. During regeneration under conditions triggering dimorphism the two morphological forms were observed after 36 h. Initially, for 10-12 h only an irregular mass was formed as a result of deregulated cell wall synthesis. Among the tested inhibitors influencing cell wall metabolism, chitin metabolism inhibitors showed distinctive effects on the regeneration of protoplasts suggesting that the respective enzymes significantly contribute to determining the morphogenesis of the dimorphic fungus B. poitrasii.

Improving extracellular production of food-use enzymes from Aspergillus nidulans

Filamentous fungi, and particularly those of the genus Aspergillus, are major producers of enzymatic activities that have important applications in the food and beverage industries. Prior to the availability of transformation systems improvement of industrial production strains was largely restricted to the strategy of mutagenesis, screening and selection. Aspergillus nidulans is a genetically amenable filamentous fungus the ease of handling and analysis of which has led to its use as a model system for the investigation of eukaryotic gene regulation. Although not used industrially it is able to produce a wide variety of extracellular enzymatic activities. As a consequence of half a century of study a considerable resource of characterised mutants has been generated in conjunction with extensive genetic and molecular information on various gene regulatory systems in this micro-organism. Investigation of xylanase gene regulation in A. nidulans as a model for the production of food-use extracellular enzymes suggests strategies by which production of these enzymes in industrially useful species may be improved.

Themes for mushroom exploitation in the 21st century: Sustainability, waste management, and conservation

Because many natural resources are limited, sustainability becomes an important concept in maintaining the human population, health, and environment. Mushrooms are a group of saprotrophic fungi. Mushroom cultivation is a direct utilization of their ecological role in the bioconversion of solid wastes generated from industry and agriculture into edible biomass, which could also be regarded as a functional food or as a source of drugs and pharmaceuticals. To make the mushroom cultivation an environmentally friendly industry, the basic biology of mushrooms and the cultivation technology must be researched and developed. This is very true for Lentinula edodes, Volvariella volvacea, and Ganoderma lucidum, which are commonly consumed in Asian communities but are now gaining popularity worldwide. Besides the conventional method, strain improvement can also be exploited by protoplast fusion and transformation. Biodiversity is the key contribution to the genetic resource for breeding programs to fulfill different consumer demands. The conservation of these mushrooms becomes essential and is in immediate need not only because of the massive habitat loss as a result of human inhabitation and deforestation, but also because of the introduced competition by a cultivar with the wild germ plasm. Spent mushroom compost, a bulky solid waste generated from the mushroom industry, however, can be exploited as a soil fertilizer and as a prospective bioremediating agent.

Chitinolytic enzymes: an exploration

Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications. Particularly, chitinases are used in agriculture to control plant pathogens. Chitinases and chitooligomers produced by enzymatic hydrolysis of chitin can also be used in human health care. The success in employing chitinases for different aspects depends on the supply of highly active preparations at reasonable cost. Therefore, the understanding of biochemistry and genetics of chitinolytic enzymes, their phylogenetic relationships and methods of estimation will make them more useful in a variety of processes in near future.

Liquid culture enhances protoplast formation from the auxotroph (ser(-)) ofLentinula edodes

The optimal conditions for the production and regeneration of the protoplasts fromLentinula edodes were studied. Protoplast formation from the mycelia ofL. edodes which were cultured in liquid medium showed a significantly high yield compared with that of the mycelia which were cultured on cellophane covered agar media. A mixture of Novozyme 234 (15 mg/ml) and Cellulase Onozuka R10 (10 mg/ml) in 0.6 M mannitol (pH 4) was optimal lytic enzyme for the protoplast release. The optimal incubation time and mycelia age were 3.5-4 hours at 30 degrees C and 6-8 days, respectively. Regeneration frequency was 0.18% plated onto a medium containing 0.6 M sucrose, and 0.08% plated onto a medium containing mannitol. But hardly any regeneration was observed in the media containing NaCl, KCl, or MgSO(4). More than 90% of the protoplasts contianed nuclei and the nucleus number per protoplast was 1.1. The DNA content per nucleus was 5.1 pg. The diameter of the protoplast was 3-5 mum and it had a well defined cell structure.

A putative role for calmodulin in the activation of Neurospora crassa chitin synthase

The possible role of calmodulin in cell wall formation and chitin synthesis was studied in Neurospora crassa by examining the effects of anti-calmodulin agents on protoplast regeneration and possible associations between chitin synthase and calmodulin related proteins in microsomal isolates. Protoplast regeneration was inhibited by trifluoperazine (> 20 microM), an anticalmodulin agent. Chitin synthase activity in microsomes was associated with that of calmodulin-dependent protein kinase and inhibited by trifluoperazine (100 microM). In vitro activity of chitin synthase was enhanced upon inclusion of calmodulin (300 ng) in the assay mix, 63% over and above the stimulation brought about by trypsin, an activator of the enzyme. Autoradiography studies on microsomal proteins revealed calmodulin-dependent phosphorylation of two microsomal calmodulin-binding proteins (106 and 89 kDa). The results indicate that calmodulin-mediated phosphorylation of specific microsomal proteins may be important in the in vivo activation of chitin synthase.

The Thom Award address. Industrial mycology and the new genetics

The genetic investigation of fungi has been extended substantially by DNA-mediated transformation, providing a supplement to more conventional genetic approaches based upon sexual and parasexual processes. Initial transformation studies with the yeast Saccharomyces cerevisiae provided the model for transformation systems in other fungi with regard to methodology, vector construction and selection strategies. There are, however, certain differences between S. cerevisiae and filamentous fungi with regard to type of genomic insertion and the availability of shuttle vectors. Single-site linked insertions are common in yeast due to the high level of homology required for recombination between vectored and genomic sequences, whereas mycelial fungi often show a high frequency of heterologous and unlinked insertions, often in the form of random and multiple-site integrations. While extrachromosomally-maintained or replicative vectors are readily available for use with yeasts, such vectors have been difficult to construct for use with filamentous fungi. The development of vectors for replicative transformation with these fungi awaits further study. It is proposed that replicative vectors may be inherently less efficient for use with mycelial fungi relative to yeasts, since the mycelium, as an extended and semicontinuous network of cells, may delimit an adequate diffusion of the vector carrying the selectable gene, thus leading to a high frequency of abortive or unstable transformants.

Paracoccidioides brasiliensis protoplast production by enzymatic treatment

The action of the enzymes novozym 234, chitinase and zymolyase 20T on the yeast-like cells of Paracoccidioides brasiliensis was studied in an attempt to obtain protoplast release. Three enzyme systems were used: the first consisted of novozym 234 and chitinase plus 0.2 M phosphate buffer, 0.9 M sorbitol and 0.5 M sodium thioglycolate; the second consisted of novozym 234, chitinase, zymolyase 20T, buffer and osmotic stabilizer, with no sodium thioglycolate; the third consisted of the same enzymes as used in the second system but at twice the concentration, plus buffer and osmotic stabilizer. Protoplasts were only released from 72-h-old cells cultured on solid peptone-yeast extract-glucose medium (PYG) treated with the third enzyme system. Sodium thioglycolate used as pretreatment favoured protoplast release but had no such action when added to the enzyme solution, possibly by altering the activity of the enzymes, novozym 234 in particular. The osmotic stabilizer used, 0.9 M sorbitol, was probably one of the factors, in addition to the enzymes, responsible for the cytoplasmic changes observed by transmission electron microscopy in yeast phase cells and in their protoplasts.

Sugar uptake by protoplasts of the ectomycorrhizal fungus, Amanita muse aria (L. ex fr.) Hooker

Protoplasts have been isolated from the ectomycorrhizal fungus, Amanita muscaria, for the first time. Yields were about 10⁸ protoplasts per g fr. wt of mycelial suspension cultures treated with a combination of Novozym 234, chitinase and cellulase Onozuka R-10, and osmotically supplemented by 0-55 M sorbitol or 035 M KC1. Silicon oil filtration was used to investigate the uptake of metabolites by protoplasts using labelled compounds. About 66% of the initial protoplast population passed the oil layer after 50 s of centrifugation. Both glucose (as well as 3-O-methylglucose) and fructose were taken up by the protoplasts but not sucrose and mannitol. The Km for glucose (fructose) uptake was 1.25 mM (11.3), V_max was 18 (30) pmoles (10⁶ protoplasts min)^-1 . Uptake of fructose was strongly inhibited by glucose but not vice versa; uptake of both was not inhibited by sucrose. The much higher affinity for glucose than for fructose suggests that glucose should be the main carbohydrate source for this fungus. Treatment of protoplasts with 10 μM antimycin A lowered cellular ATP/ADP ratios to well below 1 and significantly inhibited uptake of sugars.

Cloning of an Aspergillus niger invertase gene by expression in Trichoderma reesei

The filamentous fungus Aspergillus niger produces two glycosylated forms of the sucrose-hydrolysing enzyme, invertase. In contrast, some Trichoderma species lack invertase and are unable to utilise sucrose as a sole carbon source. Using an A. niger genomic library constructed in a cosmid vector containing the ura5 gene of Podospora anserina as a selectable marker, and the T. reesei ura5- strain as a sucrose-minus recipient strain, an A. niger invertase gene (suc1) has been cloned by a sib selection procedure. PAGE and enzyme analysis confirmed that transformants had acquired invertase activity. The cloned gene contained DNA sequences which were complementary to the amino-acid sequences of tryptic peptides found in invertase purified from A. niger. The suc1 invertase gene can be used as a dominant selectable marker for the transformation of Trichoderma strains.

Protoplast fusion of beta-glucosidase-producing Aspergillus niger strains

Protoplast fusion, induced by polyethylene glycol and Ca2+, was carried out between two auxotrophic strains of Aspergillus niger. The fusion frequency ranged from 6.2 x 10(-2) - 9.1 x 10(-2). After induced haploidization of a diploid, various segregants showing combinations of the parental genetic markers were isolated. Unlike diploids, haploid segregants exhibited greater variations in their morphology and beta-glucosidase activities. One segregant showed a 2.5-fold increase in beta-glucosidase activity over those of the parents. Thus, this method appears promising for creating new recombinant strains of A. niger with improved beta-glucosidase activities.

Transfer of isolated nuclei into protoplasts of Aspergillus nidulans

Nuclei were isolated from protoplasts of a haploid auxotrophic Aspergillus nidulans strain. Transformation of protoplasts prepared from a complementary haploid auxotrophic strain with these purified nuclei resulted in both heterokaryotic and diploid colonies. The nutritionally-complementing colonies appeared at a frequency of 5 x 10(-7) to 10(-8).