Cryopreservation at −80°C of Agaricus blazei on rice grains

Fungal cryopreservation across 61 genera: Practical application and method evaluation

Fungi occupy important environmental, cultural, and socioeconomic roles. However, biological research of this diverse kingdom has lagged behind that of other phylogenetic groups. This is partially the result of the notorious difficulty in culturing a diverse array of filamentous fungal species due to their (i) often unpredictable growth, (ii) unknown preferences for culturing conditions, and (iii) long incubation times compared with other microorganisms such as bacteria and yeasts. Given the complexity associated with concurrently culturing diverse fungal species, developing practical methods for preserving as many species as possible for future research is vital. The widely accepted best practice for preserving fungal tissue is the use of cryogenic biobanking at -165 C, allowing for the preservation and documentation of stable genetic lineages, thus enabling long-term diversity-centered research. Despite the extensive literature on fungal cryopreservation, substantial barriers remain for implementation of cryogenic biobanks in smaller mycological laboratories. In this work, we present practical considerations for the establishment of a fungal culture biobank, as well as provide evidence for the viability of 61 fungal genera in cryogenic storage. By providing a pragmatic methodology for cryogenically preserving and managing many filamentous fungi, we show that creating a biobank can be economical for independently owned and operated mycology laboratories, which can serve as a long-term resource for biodiversity, conservation, and strain maintenance.

Long-term cryopreservation of Lentinus crinitus strains by wheat grain technique

Lentinus crinitus (Basidiomycota: Polyporales) is a saprophytic fungus with biotechnological importance described more than 20 years ago. However, there are few studies on the long-term preservation of this basidiomycete. Cryopreservation is a long-term storage technique that reduces the metabolic activity of microorganisms, but its success depends on the adjustment of the freezing process, the cryoprotectants, and the protective substrates for each species. This study aimed to assess the mycelial viability and genetic stability of L. crinitus strains cryopreserved at -86 °C for two years by the wheat grain technique using different cryoprotectants and freezing methods. Three strains of L. crinitus (U9-1, U13-5, and U15-12) were subjected to different concentrations and types of cryoprotectants (dimethyl sulfoxide, glycerol, glucose, and sucrose), freezing methods such as immediate freezing from 25 to -86 °C and progressing freezing from 25 to -86 °C in a freezing container with isopropyl alcohol to control the rate of cell freezing at -1 °C min^-1, protective substrate (wheat grain and 2% malt extract agar), and cryopreservation period (1, 6, 12, and 24 months). After thawing, samples were evaluated for mycelial viability, time to mycelial recovery, mycelial stability, and genetic stability of the fungus. All techniques achieved effective cryopreservation at -86 °C, mainly with the wheat grain technique. All cryoprotectants (3.5% glycerol, 1.5% dimethyl sulfoxide, 25% sucrose, and 5% glucose), freezing methods (immediate and gradual), and protective substrate (wheat grain and malt extract agar) were effective for cryopreservation of the three L. crinitus strains in an ultra-low temperature freezer for two years. Mycelial viability, mycelial stability, and genetic stability of the fungus were not affected after two-year cryopreservation, evidencing the robustness of the long-term cryopreservation technique and the fungus.

Endophytic fungi of Brunfelsia uniflora: isolation, cryopreservation, and determination of enzymatic and antioxidant activity

Brunfelsia uniflora (Pohl.) D. Don (Solanaceae), commonly known as manacá-de-cheiro, is widely distributed in Brazil and used by local indigenous peoples as an antirheumatic, antisyphilitic, depurative, emetic, vermifuge, and purgative agent. Several studies have examined the biological activities and phytochemical profile of Brunfelsia; however, few have focused on the diversity of endophytic microorganisms that colonize members of the genus. This study aimed to isolate and cryopreserve endophytic fungi from B. uniflora and determine their cellulase, laccase, and antioxidant activities. Endophytic fungi were isolated from B. uniflora stems, cultured on wheat grains, immersed in a 150 g L^-1 aqueous sucrose solution, and cryopreserved at - 80 °C for 1 and 6 months. Cellulase activity was determined by a qualitative test using carboxymethylcellulose medium and laccase activity by a quantitative test based on the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate). Prior to antioxidant activity assays, fungi were grown in malt extract broth for production of mycelial biomass. A methanolic extract was prepared for evaluation of DPPH· scavenging activity, FRAP activity, and total phenolic content. A total of 46 endophytic fungal isolates were obtained from B. uniflora stems and classified into 24 groups according to morphological similarities. B. uniflora was shown to harbor different genera of ascomycete fungi as endophytic organisms. Mycelial viability was observed after 1 and 6 months of cryopreservation at - 80 °C. Fungi exhibited cellulase and laccase activities. Isolate CE23 had the highest laccase activity after 7 days of cultivation. Twelve isolates were found to have low total phenolic contents and DPPH· and FRAP activities.

Five-year cryopreservation at -80 °C of edible and medicinal basidiomycetes by wheat grain technique

This research has focused on basidiomycete cryopreservation at -80 °C and developed a cryopreservation method based on the use of hard or medium-hard endosperm wheat grains as a mycelial carrier for cryopreservation. The aim of this study was to evaluate the mycelial viability of edible and medicinal basidiomycetes, using 13 strains of Agaricus spp. and eight strains of non-Agaricus spp., cryopreserved at -80 °C on hard endosperm wheat grain, with or without cryoprotectant agent (4% glucose), for two and five years. Two groups of basidiomycetes, Agaricus genus and other non-Agaricus genera, were cryopreserved at -80 °C by wheat grain technique for two and five years. The cryopreservation technique with hard endosperm wheat grain without cryoprotectant (preservation substrate), settled previously for A. subrufescens is efficient to cryopreserve other basidiomycetes such as Lentinus crinitus, Pleurotus ostreatus, Pleurotus eryngii, Schizophyllum commune, and Lentinula edodes, besides A. subrufescens strains.

Semisolid culture medium improves mycelial recovery of Agaricus subrufescens cryopreserved in cereal grains

This study aimed to evaluate the effects of the solid and semisolid culture medium on the mycelial viability of A. subrufescens after 5-year cryopreservation at - 70 °C. Mycelia were grown in three types of whole or ground grains, with or without 5% glycerol addition in the substrate and/or in a cryotube. After 5 years of cryopreservation at - 70 °C, every treatment was thawed and recovered in malt extract culture medium with 15 (solid culture medium) or 5 g L-1 (semisolid culture medium) of agar. The semisolid recovery culture medium increased the mycelial viability recovery capacity of A. subrufescens cryopreserved for 5 years in grains with glycerol only in the cryotube, and specifically with medium-hard wheat grain without glycerol addition at all. Agar-based substrates such as malt extract agar, agar-ground grain, or the one with glycerol addition to the substrate were not effective to keep the mycelial viability, regardless of the recovery culture medium consistency. Hard and medium-hard endosperm wheat grains or hard endosperm rye grains with addition of glycerol as cryoprotectant only to the cryotube were effective to cryopreserve the fungus for 5 years without cryoprotectant addition in the substrate.

Long-term cryopreservation of basidiomycetes

Basidiomycetes have several biotechnological and industrial applications such as enzyme production, bioremediation, pharmaceutical and functional food production. Due to climatic features, the preservation of several basidiomycetes is threatened, and to guarantee the preservation of this genetic resource, the development of long-term preservation techniques is necessary once there is no universal protocol for the cryopreservation of basidiomycetes. Cryopreservation is a technique in which microorganisms are submitted to ultralow temperatures. Therefore, this study aimed to collect information on the main conditions for long-term cryopreservation of basidiomycetes in the last 20 years. Scientific articles on cryopreservation of basidiomycetes published from 1997 to 2016, were researched, and only the studies on two intervals of cryopreservation were considered: from 1 to 2 years and for longer than 2 years. The analyzed conditions of basidiomycete cryopreservation were: most studied genera, cryopreservation temperature, substrate, cryoprotectant (and preservation substrate), cryopreservation period, thawing temperature and cultivation medium after thawing, physiological and genetic stability of basidiomycetes after thawing in cryopreservation. In this review, the viability of the main cryopreservation conditions of basidiomycetes studied in the last 20 years are presented and discussed.

Cryopreservation at -75°C of Agaricus subrufescens on wheat grains with sucrose

Agaricus subrufescens is a basidiomycete which is studied because of its medicinal and gastronomic importance; however, less attention has been paid to its preservation. This study aimed to evaluate the effect of sucrose addition to substrate and cryotube on the viability of Agaricus subrufescens cryopreserved at −20 °C and at −75 °C for one and two years. Zero, 10% or 20% sucrose was added to potato dextrose agar or wheat grain. The mycelia were cryopreserved in the absence of cryoprotectant or with sucrose solutions at 15%, 30% or 45%. After one or two years at −75 °C or at −20 °C, mycelia were thawed and evaluated about viability, initial time of growth, colony diameter and genomic stability. Cryopreservation at −20 °C is not effective to keep mycelial viability of this fungus. Cryopreservation at −75 °C is effective when sucrose is used in substrates and/or cryotubes. Without sucrose, cryopreservation at −75 °C is effective only when wheat grains are used. Physiological characteristic as mycelial colony diameter is negatively affected when potato dextrose agar is used and unaffected when wheat grain is used after two-year cryopreservation at −75 °C. The fungus genome does not show alteration after two-year cryopreservation at −75 °C.

Viability of ectomycorrhizal fungi following cryopreservation

The use of ectomycorrhizal (ECM) fungi in biotechnological processes requires their maintenance over long periods under conditions that maintain their genetic, phenotypic, and physiological stability. Cryopreservation is considered as the most reliable method for long-term storage of most filamentous fungi. However, this technique is not widespread for ECM fungi since many do not survive or exhibit poor recovery after freezing. The aim of this study was to develop an efficient cryopreservation protocol for the long-term storage of ECM fungi. Two cryopreservation protocols were compared. The first protocol was the conventional straw protocol (SP). The mycelium of the ECM isolates was grown in Petri dishes on agar and subsequently collected by punching the mycelium into a sterile straw before cryopreservation. In the second protocol, the cryovial protocol (CP), the mycelium of the ECM isolates was grown directly in cryovials filled with agar and subsequently cryopreserved. The same cryoprotectant solution, freezing, and thawing process, and re-growth conditions were used in both protocols. The survival (positive when at least 60 % of the replicates showed re-growth) was evaluated before and immediately after freezing as well as after 1 week, 1 m, and 6 m of storage at -130 °C. Greater survival rate (80 % for the CP as compared to 25 % for the SP) and faster re-growth (within 10 d for the CP compared to the 4 weeks for the SP) were observed for most isolates with the CP suggesting that the preparation of the cultures prior to freezing had a significant impact on the isolates survival. The suitability of the CP for cryopreservation of ECM fungi was further confirmed on a set of 98 ECM isolates and displayed a survival rate of 88 % of the isolates. Only some isolates belonging to Suillus luteus, Hebeloma crustuliniforme, Paxillus involutus and Thelephora terrestris failed to survive. This suggested that the CP is an adequate method for the ultra-low cryopreservation of a large set of ECM fungi and that further studies are necessary for the more recalcitrant ones.

Preservation of Agaricus subrufescens strains at low temperature by using cultures on sorghum grains

BACKGROUND

One of the main problems for the preservation of genetics resources of Agaricus subrufescens is to maintain the viability of the strains because the mycelium is very sensitive to cooling and therefore it ages rapidly.

AIMS

Evaluate the viability of A. subrufescens strains stored as cultures on sorghum grain (spawn) at different temperatures.

METHODS

Eighteen strains of A. subrufescens and three strains of Agaricus bisporus were studied. Spawn's viability was evaluated under the following conditions: (1) control at 25°C (C), (2) cooling to 4°C (R) and (3) freezing in liquid nitrogen at -196°C (LN). Samples were recovered from week 4 every 2 weeks until week 12 and week 24 in C and R, whereas in LN samples were recovered at 4, 12 and 24 weeks. Viability was evaluated in 50 seeds, by strain and condition, recovering the mycelium in Petri dishes with potato dextrose agar medium (PDA). Mycelium growth was also evaluated on PDA after 14 days of recovery.

RESULTS

Most strains showed 100% viability and they were recovered usually in 1 day. In LN the viability ranged between 84 and 100% depending on the strain, but in some cases recovery took more than 10 days. Mycelial growth decreased gradually over time and although the results show significant differences between treatments C and R, the decline is associated with ageing of the mycelium rather than the treatment itself.

CONCLUSIONS

Culture on sorghum grain and storage at low temperature is an interesting way to preserve genetic resources of A. subrufescens.

Cryopreservation at -20 and -70 °C of Pleurotus ostreatus on Grains

Alternative substrates for cryopreservation at -20 °C have been little explored for basidiomycetes and could bring new possibilities of lower cost cryopreservation. Nevertheless, freezing temperatures between -15 and -60 °C are very challenging because they frequently result in cryoinjuries. The objective of this study was to evaluate substrates associated to cryoprotective agents for Pleurotus ostreatus cryopreservation at -20 or -70 °C in order to develop alternative techniques for basidiomycete cryopreservation. P. ostreatus was grown on potato dextrose agar or whole grains of oat, wheat, rice or millet and transferred to cryovials with cryoprotective solution with 1 % dimethyl sulfoxide, 5 % glycerol, 10 % saccharose, 4 % glucose, 6 % polyethylene glycol-6000 or 5 % malt extract. The mycelium in the cryovials were cryopreserved at -20 or -70 °C and recovered for evaluation of the mycelial growth viability after 1 and 3 years. Both substrates and cryoprotectants affect the viability of the mycelial growth cryopreserved at -20 or -70 °C; wheat grains combined with cryoprotectants such as saccharose or glucose are effective for keeping mycelium viable after cryopreservation at -20 °C for 1 or 3 years; for cryopreservation at -70 °C after 1 or 3 years, any substrate combined with any cryoprotectant is effective for preserving the mycelium viable, except for millet grains with polyethylene glycol after 3 years; semi-permeable cryoprotective agents such as saccharose and glucose are the most effective for cryopreservation at -20 or -70 °C for at least 3 years.