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

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.

Iron-enriched mycelia of edible and medicinal basidiomycetes

Iron bioaccumulation in basidiomycetes is an alternative to recover ferrous sulphate from titanium dioxide pigment production and to produce an iron-enriched mycelial biomass. This study aimed to evaluate iron bioaccumulation capacity in vegetative mycelium of edible and medicinal fungi grown in malt extract liquid medium with different ferrous sulphate contents. Five basidiomycetes were grown in malt extract liquid medium with different iron contents from 0.116 to 100 mg L^-1 iron. The iron content of dried mycelial biomass bioaccumulated with iron was determined by flame atomic absorption spectrophotometry. All fungi grew on the iron culture media and the mycelial biomass growth ranged from 3.24 ± 0.65a mg mL^-1 to 12.46 ± 0.29 mg mL^-1. Iron addition to culture media increased the iron content in the mycelial biomass from 4000-13,000-fold compared with control. Pleurotus ostreatus (2181 ± 218 mg kg^-1) presented the greatest iron content in the mycelial biomass, followed by Schizophyllum commune (1769 ± 131 mg kg^-1), Agaricus subrufescens (1272 ± 8.84 mg kg^-1), and Ganoderma lucidum (840 ± 75 mg kg^-1). P. ostreatus, followed by S. commune, and G. lucidum at 90 and 100 mg L^-1 iron in the culture medium are the best choices to produce iron-enriched mycelial biomass. This extensive study of several edible and medicinal basidiomycetes grown in different iron contents was effective in recovering ferrous sulphate byproduct and transferring it to mycelium to produce a new nutraceutical food of iron-enriched mycelial biomass.

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.