Statistical optimization of process variables for the large-scale production of Metarhizium anisopliae conidiospores in solid-state fermentation

Solid-State Fermentation: Applications and Future Perspectives for Biostimulant and Biopesticides Production

With the expansion of the green products market and the worldwide policies and strategies directed toward a green revolution and ecological transition, the demand for innovative approaches is always on the rise. Among the sustainable agricultural approaches, microbial-based products are emerging over time as effective and feasible alternatives to agrochemicals. However, the production, formulation, and commercialization of some products can be challenging. Among the main challenges are the industrial production processes that ensure the quality of the product and its cost on the market. In the context of a circular economy, solid-state fermentation (SSF) might represent a smart approach to obtaining valuable products from waste and by-products. SSF enables the growth of various microorganisms on solid surfaces in the absence or near absence of free-flowing water. It is a valuable and practical method and is used in the food, pharmaceutical, energy, and chemical industries. Nevertheless, the application of this technology in the production of formulations useful in agriculture is still limited. This review summarizes the literature dealing with SSF agricultural applications and the future perspective of its use in sustainable agriculture. The survey showed good potential for SSF to produce biostimulants and biopesticides useful in agriculture.

From the dual cyclone harvest performance of single conidium powder to the effect of Metarhizium anisopliae on the management of Thaumastocoris peregrinus (Hemiptera: Thaumastocoridae)

Insect pests introduced in eucalyptus plantations in Brazil are mostly of Australian origin, but native microorganisms have potential for their management. High quality biopesticide production based on entomopathogenic fungi depends on adequate technologies. The objective of this study was to evaluate Mycoharvester® equipment to harvest and separating particles to obtain pure Metarhizium anisopliae conidia to manage Thaumastocoris peregrinus Carpintero & Dellapé, 2006 (Hemiptera: Thaumastocoridae). The Mycoharvester® version 5b harvested and separated M. anisopliae spores. The pure conidia were suspended in Tween 80® (0.1%) and calibrated to the concentrations of 1 x 106, 107, 108 and 109 conidia/ml to evaluate the pathogenicity, lethal concentration 50 and 90 (LC50, LC90) and lethal time 50 and 90 (LT50, LT90) of this fungus to T. peregrinus. This equipment harvested 85% of the conidia from rice, with production of 4.8 ± 0.38 x 109 conidia/g dry mass of substrate + fungus. The water content of 6.36% of the single spore powder (pure conidia) separated by the Mycoharvester® was lower than that of the agglomerated product. The product harvested at the concentrations of 108 and 109 conidia/ml caused high mortality to T. peregrinus third instar nymphs and adults. The separation of conidia produced by solid-state fermentation with the Mycoharvester® is an important step toward optimizing the fungal production system of pure conidia, and to formulate biopesticides for insect pest management.

Evaluation of ultrasound waves for the production of chitinase and β-1,3 glucanase by Trichoderma harzianum through SSF

Cell wall degrading enzymes (chitinase and β-1,3-glucanase) were produced by solid-state fermentation (SSF) using the fungus Trichoderma harzianum and different agro-industrial products, mainly residues. The influence of temperature (25-35 °C), initial moisture content (50-90% w/w), nutrient solution (1-2% v/w), and yeast extract (1-2% w/w) on enzyme activity was evaluated. The application of ultrasound during fermentation for different times (0-6 h/day) was also studied. White rice was the substrate that showed the highest chitinase and β-1,3-glucanase activities, which were 31.31 U/g for chitinase and 23.83 U/g for β-1,3-glucanase after 10 days of fermentation. Application of ultrasound waves during fermentation positively affected (p < 0.05) the enzyme activities. The best results for chitinase (51.88 U/g) and β-1,3-glucanase (39.22 U/g) were obtained with a 50% (w/w) moisture content and 4 h/day ultrasound application for 10 days of fermentation. Increases of 3.6-fold (from 14.37 to 51.88 U/g) and 3.8-fold (from 10.22 to 39.22 U/g) in activities for chitinase and β-1,3-glucanase, respectively, compared to non-sonicated fermentation, were obtained. Ultrasound technique associated with the SSF process was a promising alternative to increase the production activity of cell wall degrading enzymes: chitinase and β-1,3-glucanase.

Cellulase production by Aspergillus niger using urban lignocellulosic waste as substrate: Evaluation of different cultivation strategies

Cellulases are used in various industries, acting efficiently and sustainably in the degradation of cellulose contained in different raw materials and recovering high value products. It is the third largest group of enzymes consumed industrially, as they are required in processes linked to the food, biofuel, textile, cleaning products, among others. However, the main disadvantage in the use of commercial cellulases is the high cost. In this context, the objective of this work was to determine conditions for obtaining more efficient and economical cellulases. For this, the efficiency in obtaining the extracellular cellulases endoglucanase (CMCase) and exoglucanase (FPase) by a fungus Aspergillus niger was investigated using an urban lignocellulosic waste as substrate characterized by tree leaves collected from squares and avenues in urban areas. As urban lignocellulosic waste is an innovative raw material, its chemical composition was determined. This substrate contains 20.36% cellulose and induced the production of cellulases in all fermentation methods, proving to be a promising and sustainable source. The influence of the nutrient medium on CMCase and FPase activities was evaluated for three different sequential fermentation (SF) configurations. Medium 2 provided an increase of up to 100 U/L of CMCase and FPase in relation to medium 1. The interactive effect of pH and moisture content on CMCase e FPase production under SF was studied in a central composite design (CCD). Also, different fermentation methods (solid state, submerged and sequential) were evaluated. The use of SF increased the enzymatic activities of both cellulases by 140% compared to other conventional methods and also stood out in the production of proteins (270.05 μg/mL) and reducing sugars (1.19 mg/mL). The desirability function determined the optimal activities of CMCase and FPase as 413.49 U/L and 230.68 U/L, respectively, obtained from the optimal variables of pH 5.5 and 75% moisture content under SF. The effect of pH and moisture content on the activity of each cellulase was analyzed using the Pareto chart and response surface methodology (RSM). These results revealed favorable strategies for cellulase production, such as the use of urban lignocellulosic waste, SF and ideal operational conditions.

Characterization of a new strain of Metarhizium novozealandicum with potential to be developed as a biopesticide

The fungal species Metarhizium novozealandicum, that occurs only in New Zealand and Australia has been poorly studied.  In this work, a new strain of M. novozealandicum isolated from a larva of Wiseana sp. is described based on morphology, genomic multilocus (ITS, EF-1α and β-tubulin) phylogeny, growth in different culture media and insecticidal activity. The isolate AgR-F177 was clustered in the same clade with M. novozealandicum. AgR-F177 colonies developed faster on Sabouraud Dextrose Agar (SDA) than on Potato Dextrose Agar (PDA) when incubated at 25°C, with no growth observed at 30°C on either media. Conidia yield on an oat-based medium in semisolid fermentation was 7.41 x 10⁸conidia/g of substrate and a higher yield of 1.68 x 10⁹conidia/g of substrate was obtained using solid fermentation on cooked rice. AgR-F177 formed microsclerotia (MS) in liquid fermentation after 7 days reaching the maximum yield of 3.3 × 10³ MS/mL after 10 days. AgR-F177 caused mortality in Wiseana copularis, Costelytra giveni and Plutella xylostella larvae with efficacies up to 100%, 69.2%, and 45.7%, respectively. The ease of production of AgR-F177 with different fermentation systems and its pathogenicity against different insect pests reveal its potential as a new biopesticide.

Metarhizium robertsii protease and conidia production, response to heat stress and virulence against Aedes aegypti larvae

Nutritional factors exert significant influence on the growth of entomopathogenic fungi, one of the main agents employed commercially in the biological control of arthropods. Thus, the objective of this work is to optimize the culture medium and solid fermentation time for production of proteases and conidia of Metarhizium robertsii ARSEF 2575 and to evaluate the interference of riboflavin and salts on virulence and resistance to abiotic stress factors. In the first step, nine groups were separated: negative control, positive control, and seven supplementation groups: ammonium nitrate, ammonium chloride, potassium nitrate, sodium nitrate, ammonium sulfate, ammonium phosphate, urea. Sodium nitrate showed significant difference in protease production at the time of 20 days of solid fermentation. Then, different concentrations of sodium nitrate and riboflavin as supplement were evaluated. Response surface methodology demonstrated that riboflavin and sodium nitrate influence proteolytic activity and conidia production, but without synergism. Supplementation of the medium with the optimal concentration of sodium nitrate and riboflavin did not interfere with the germination of conidia without exposure to abiotic stress, but did increase the thermotolerance of conidia. The presence of riboflavin and sodium nitrate at optimal concentrations in the culture medium did not alter fungal virulence with and without exposure to heat stress, varying according to the presence or absence of the supernatant during exposure, evidencing that resistance to heat exposure is multifactorial and dependent on intra- and extracellular factors. Moreover, the supplementation increased the larvicidal activity of the supernatant against Aedes aegypti.

Scanning agro-industrial wastes as substrates for fungal biopesticide production: Use of Beauveria bassiana and Trichoderma harzianum in solid-state fermentation

As a waste valorisation option, agro-industrial residues (rice husk, apple pomace, whisky draff, soy fiber, rice fiber, wheat straw, beer draff, orange peel and potato peel) were tested as feasible substrates for fungal conidia production. Solid-state fermentation tests were conducted at laboratory scale (100 g) with Beauveria bassiana or Trichoderma harzianum which conidia are reported to have biopesticide properties. Conidia concentrations with all substrates were at least two orders of magnitude above inoculum except for both fibers, thus demonstrating the possibilities of the proposed waste recovery option. Highest productions were at least 1 × 10⁹ conidia g^-1 dry matter for Beauveria bassiana using rice husk or potato peel and higher than 5 × 10⁹ conidia g^-1 dry matter for Trichoderma harzianum using beer draff, potato peel or orange pomace. Principal component analysis has been used to understand which parameters affect the most fungal conidia production for an easier evaluation of other similar wastes, being air-filled porosity and initial pH for Beauveria bassiana and cumulative oxygen consumption, initial moisture and total sugar content for Trichoderma harzianum.

DNA methyltransferase implicated in the recovery of conidiation, through successive plant passages, in phenotypically degenerated Metarhizium

Metarhizium robertsii is a fungus with two lifestyles; it is a plant root symbiont and an insect pathogen. A spontaneously phenotypically degenerated strain of M. robertsii strain ARSEF 2575 (M. robertsii lc-2575; lc = low conidiation) showed a reduction in conidiation and fungal virulence after successive subculturing on agar medium. In order to recover conidiation, we experimentally passaged M. robertsii lc-2575 through plant (soldier bean and switchgrass) root or insect (Galleria mellonella) larvae. After five passages, the resultant strains had significantly increased conidial yields on agar and increased virulence in insect bioassays. Concomitantly, DNA methyltransferase, MrDIM-2 expression was downregulated in BR5 (a strain after 5 bean root passages) and isolates after switchgrass and insect passages. Bisulfite sequencing showed little difference in overall genomic DNA methylation levels (~ 0.37%) between M. robertsii lc-2575 and BR5. However, a finer comparison of the different methylated regions (DMRs) showed that DMRs of BR5 were more abundant in the intergenic regions (69.32%) compared with that of M. robertsii lc-2575 (33.33%). The addition of DNA methyltransferase inhibitor, 5-azacytidine, to agar supported the role of DNA methyltransferases and resulted in an increase in conidiation of M. robertsii lc-2575. Differential gene expression was observed in selected DMRs in BR5 when compared with M. robertsii lc-2575. Here we implicated epigenetic regulation in the recovery of conidiation through the effects of DNA methyltransferase and that plant passage could be used as a method to recover fungal conidiation and virulence in a phenotypically degenerated M. robertsii. KEY POINTS: • Passage of Metarhizium through plant root or insect results in increased conidiation. • DNA methyltransferase is downregulated after host passage. • Bisulfite sequencing identified potentially methylated genes involved in conidiation.

Molecular characterization of pathogenesis involving the GAS 1 gene from Entomopathogenic fungus Lecanicillium lecanii and its virulence against the insect host Diaphorina citri

The entmopathogenic fungus Lecaniicillium lecanii is a naturally available biological control and it is considered to be one of the best mycoinsecticide agents against the destructive insect pest Diaphorina citri Kuwayama. The present study aimed to extract and characterize the toxic insecticidal protein from L. lecanii and to assess the toxicity level against the Asian citrus psyllid the vector of Huanglongbing disease (HLB), also called citrus greening. Extracts of a toxic substance from submerged batch culture examined by sodium dodecyl sulfate-poly-acrylamide (SDS-PAGE), had a molecular weight of 45 kDa. The most abundant toxic metabolite was subjected to HPLC to purify and identified it by mass spectrometry. Subsequently, metabolite toxicity was tested against D. citri at three different concentrations (1%, 2%, and 3%). The results showed that the highest concentration had a significant maximum mortality at 120 h post application. Furthermore, we investigated the expression of the GAS1 gene which was previously identified to have a role in pathogenicity in in vivo studies in adult insect psyllids. Results of this study indicated that expression of the virulence factor gene was present at three concentrations of the fungal suspension post inoculation. This is the first study to provide this novel approach for the characterization of fungal mediated synthesis of a cuticle degrading soluble protein against the insect D. citri. The present results provide strong information on the in vivo expression of the GAS1 gene involved in fungal virulence pertaining to penetration of the insect cuticle, but not to inhibiting the growth of the host.

Isolation and characterization of Metarhizium anisopliae TK29 and its mycoinsecticide effects against subterranean termite Coptotermes formosanus

The entomopathogenic fungus Metarhizium anisopliae is widely used as biocontrol agent against many insect pests. In the present study, the potential isolate of M. anisopliae TK29 was isolated from the agricultural soils in Thekkady, India. The taxonomic identity of the isolate was confirmed based on its morphology and 18S rDNA gene sequence homology. Phylogenetic analysis confirmed that the isolated strains were related to the same species. A potential isolate (TK29) was optimized for mass cultivation and conidial spore production was enhanced using three different raw substrates (Rice, Maize, black gram) by solid-state fermentation. The results showed higher conidial spore yield from rice (2.6 ± 0.32%) compared to black gram (2.1 ± 0.28%) and maize (1.9 ± 0.23%) substrates. Dry green conidia were applied against Formosan subterranean termite, Coptotermes formosanus at three different concentrations (1 × 10⁶, 1 × 10⁷, and 1 × 10⁸ conidia/ml^-1). The highest mortality rate was obtained from 1 × 10⁸ conidia/ml^-1 at 120 h post-treatment. Our study indicated that M. anisopliae TK29 had desirable attributes for the development of a mycoinsecticide against C. formosanus.

Solid state fermentation (SSF): diversity of applications to valorize waste and biomass

Solid state fermentation is currently used in a range of applications including classical applications, such as enzyme or antibiotic production, recently developed products, such as bioactive compounds and organic acids, new trends regarding bioethanol and biodiesel as sources of alternative energy, and biosurfactant molecules with environmental purposes of valorising unexploited biomass. This work summarizes the diversity of applications of solid state fermentation to valorize biomass regarding alternative energy and environmental purposes. The success of applying solid state fermentation to a specific process is affected by the nature of specific microorganisms and substrates. An exhaustive number of microorganisms able to grow in a solid matrix are presented, including fungus such as Aspergillus or Penicillum for antibiotics, Rhizopus for bioactive compounds, Mortierella for biodiesel to bacteria, Bacillus for biosurfactant production, or yeast for bioethanol.

Modulation of conidia production and expression of the gene bbrgs1 from Beauveria bassiana by oxygen pulses and light

Light and oxidant states affect the conidiation in diverse fungi, although the response has not been described when both stimuli are applied simultaneously. Conidial production and quality in Beauveria bassiana were analysed under four conditions for a wild-type (wt) strain and a previously isolated mutant (mt): normal atmosphere (21% O2; NA) or oxygen-enriched pulses (26% O2; OEP), with either light (L) or darkness (D). The response was complemented by following the expression of the bbrgs1 gene, encoding a regulator of the G-protein signal associated to conidia production. Conidiation was not significantly affected in the mutant strain by any condition (highest value with NA-L: 2.7×10(8)concm(-2)). Relative to maximal levels under NA (NA-D: 4×10(7)concm(2)), the wt strain diminished conidiation by 34-fold under OEP. The expression of bbrgs1 was higher (up to 188 times) in the mutant strain in every condition relative to the wt strain, in fact expression levels were consistent with the conidiation yields between strains. Viability and hydrophobicity were less affected by culture conditions, although pathogenicity parameters improved in conidia from OEP. The response to OEP, either with light or darkness, was strain-dependent for conidial production, viability, hydrophobicity and infectivity of conidia, then these parameters could be modulated in mass production processes.

Exo-pectinase production by Bacillus pumilus using different agricultural wastes and optimizing of medium components using response surface methodology

In this research, the production of exo-pectinase by Bacillus pumilus using different agricultural wastes was studied. Agricultural wastes containing pectin such as wheat bran, sugar beet pulp, sunflower plate, orange peel, banana peel, apple pomace and grape pomace were tested as substrates, and activity of exo-pectinase was determined only in the mediums containing sugar beet pulp and wheat bran. Then, effects of parameters such as concentrations of solid substrate (wheat bran and sugar beet pulp) (A), ammonium sulphate (B) and yeast extract (C) on the production of exo-pectinase were investigated by response surface methodology. First, wheat bran was used as solid substrate, and it was determined that exo-pectinase activity increased when relatively low concentrations of ammonium sulphate (0.12-0.21% w/v) and yeast extract (0.12-0.3% w/v) and relatively high wheat bran (~5-6% w/v) were used. Then, exo-pectinase production was optimized by response surface methodology using sugar beet pulp as a solid substrate. In comparison to P values of the coefficients, values of not greater than 0.05 of A and B (2) showed that the effect of these process variables in exo-pectinase production was important and that changes done in these variables will alter the enzyme activity.

Expression and promoter characterization of BbPacC, a pH response transcription factor gene of the entomopathogenic fungus Beauveria bassiana

To survive, the entomopathogenic fungus Beauveria bassiana, which shows promise as a biocontrol agent for a variety of pests, including agricultural and forestry pests and vectors of human pathogens, must tailor gene expression to the particular pH of its environment. The pH response transcription factor gene BbPacC and its flanking sequence were cloned from this fungus. Quantitative reverse transcription (RT)-PCR revealed that it is highly induced by alkaline pH and salt stress, and the expression level achieved twice that of the housekeeping gene γ-actin. A microfluorometric assay indicated that the 1479 bp promoter region could activate the expression of enhanced green fluorescent protein (EGFP) under the same conditions. Truncation analysis showed that the 1479, 1274, 1040, 888 and 742 bp promoters have similar efficiencies in activating expression of β-glucuronidase (GUS). The GUS activities of corresponding transformants reached approximately 50 % that of those containing the strong constitutive promoter PtrpC. A truncation upstream at the –572 bp position (referenced to the translation start codon ATG), however, resulted in a significant loss of GUS activity. Both the upstream absences of the −502 and −387 bp positions caused almost complete loss of GUS activity. These results suggest that PPacC is an efficient, alkaline, and salt-inducible promoter, the core cis-elements are mainly located within the –742 to –502 bp region, and promoters equal to or longer than 742 bp may be feasible for regulating gene expression in response to an ambient pH or salt stress.

Nutritional optimization of a native Beauveria bassiana isolate (HQ917687) pathogenic to housefly, Musca domestica L

A new Beauveria bassiana isolate, showing high activity against Musca domestica L. (Diptera: Muscidae) adults (mortality-100.0 %), larvae (mortality-72.3 %) and pupae (Infection in emerged flies-96.7 %) was used. The isolate was subjected to a combinational approach towards selection of process parameters for its growth optimization. Initial screening of several carbon and nitrogen sources revealed glucose and NaNO3 as the most suitable source for optimal biomass and spore production. Further, optimization through Placket-Burman and a 2(5) full factorial central composite design revealed highly significant effect of glucose and pH. The optimum composition for maximum biomass yield was (g/l): glucose 28; NaNO3 2.43; KH2PO4 1.32; MgSO4 0.60; and pH 7.00. Glucose concentration showed almost linear relationship with biomass yield, indicating its significant contribution in medium composition for fungal growth. Highly significant interactions were observed between glucose and pH, followed by glucose and NaNO3 concentration.

Production of fibrolytic enzymes by Aspergillus japonicus C03 using agro-industrial residues with potential application as additives in animal feed

Solid-state fermentation obtained from different and low-cost carbon sources was evaluated to endocellulases and endoxylanases production by Aspergillus japonicus C03. Regarding the enzymatic production the highest levels were observed at 30 °C, using soy bran added to crushed corncob or wheat bran added to sugarcane bagasse, humidified with salt solutions, and incubated for 3 days (xylanase) or 6 days (cellulase) with 70% relative humidity. Peptone improved the xylanase and cellulase activities in 12 and 29%, respectively. The optimum temperature corresponded to 60 °C and 50-55 °C for xylanase and cellulase, respectively, both having 4.0 as optimum pH. Xylanase was fully stable up to 40 °C, which is close to the rumen temperature. The enzymes were stable in pH 4.0-7.0. Cu++ and Mn++ increased xylanase and cellulase activities by 10 and 64%, respectively. A. japonicus C03 xylanase was greatly stable in goat rumen fluid for 4 h during in vivo and in vitro experiments.

Response surface optimization of polysaccharides extraction from Liriope roots and its modulatory effect on Sjogren syndrome

The response surface methodology (RSM) was employed to study the extraction of liriope polysaccharides. The maximum extraction rate (64.1%) of liriope polysaccharides obtained by using the above optimised concentrations of the variables was extraction time (X(1)) at 185min, ratio of liquid to solid (X(2)) at 11, and extraction temperature (X(3)) at 94 degrees C. Forty male Wistar rats were used in the present experiment. After 2 weeks of acclimatization, animals were divided into 5 equal groups: control, SS model and 3 polysaccharides-treatment groups. Rats were orally administered their respective doses every day for 6 weeks. Liriope polysaccharides significantly increased the amount of salivary secretion, and the relative weight of spleen, thymus and submandibular glands. Therefore, the present results revealed that liriope polysaccharides exert a protective effect against tissue damage in rats with sjogren syndrome (SS).