Screening for alkaline keratinolytic activity in fungi isolated from soils of the biosphere reserve “Parque Costero del Sur” (Argentina)

Abstract

A screening was carried out on 69 fungal strains isolated from alkaline-calcareous, neutral and alkaline-sodic soils, as well as from their associated plant material, to determine their ability to grow at alkaline pH. A total of 32 fungi were selected for their ability to produce alkaline keratinase activity in submerged shaken cultures supplemented with soybean meal (SM) and tryptone and on cow hair (CH) under solid state fermentation conditions. Although several fungal strains produced keratinolytic activity on both SM and CH, they differed in the levels detected. Among them, Aspergillus niger, Cladosporium cladosporioides, Metarrhizium anisopliae, Neurospora tetrasperma and Westerdikella dispersa were the best producers, with levels higher than 1.2 U ml -1 . Different fungal species are here reported for the first time for their ability to produce keratinolytic activity at alkaline pH.

Biodegradation of feather waste keratin by a keratinolytic soil fungus of the genus Chrysosporium and statistical optimization of feather mass loss

“…After 42 days of cultivation A. fulvescens strains and Chrysosporium articulatum strain caused solubilisation and mineralization of feather proteins as indicated by the release of peptides and the accumulation of N-NH 4 + in the medium correlated with increased pH reaching 8.6–9.1 (alkalinization). As reported by Sanyal et al (1985) and Elíades et al (2010), an alkaline reaction is favourable for the production of keratinolytic protease by fungi. Korniłłowicz-Kowalska (1997a) demonstrated that saprotrophic keratinolytic fungi, represented mainly by a variety of species of geophilic dermatophytes and Chrysosporium , converted up to 75% of nitrogen into the ammonium form during full solubilization of native feather keratin.…”

α‐L‐Rhamnosidase andβ‐D‐glucosidase activities in fungal strains isolated from alkaline soils and their potential in naringin hydrolysis

“…All the fungi isolated were inoculated according to Saparrat and Guillen [32] in a liquid soya-meal medium as reported by Elíades et al [22], and supplemented with buffer-solutions according to Nagai et al [33] to adjust the pH to 9.0. Three replicates for each fungus were incubated for 15 d at 28 ± 1.5 °C under shaking (200 rpm).…”

“…Twenty-three fungi from the screening were grown on the soya-meal liquid medium at pH 9.0 (basal medium) [22] and in the presence of naringin (Sigma, USA, with purity higher than 99.5% purity). A stock solution of 1 mM of this glucoside in Tris-HCl 20 mM was sterilized by filtration through 0.2 μm cellulose filters and added to the basal medium before inoculating each fungus as reported by Saparrat et al [6].…”

“…α-L-Rhamnosidase and β-D-glucosidase activities were measured at pH 9.0 through either a microtiter plate method (qualitatively) or spectrophotometric analysis (quantitatively) using the chromogen substrates p-nitrophenyl-α-L-rhamnopyranoside (Sigma, St. Louis, MO, USA; pnp-Rha) and p-nitrophenyl-β-D-glucopyranoside (Sigma, pnp-Glu) respectively, according to Rojas et al [34]. Culture filtrates previously concentrated as reported by Elíades et al [22] were used as enzyme source. Blank reactions without enzyme were also tested.…”

“…Therefore, new biocatalysts with a better performance, such as those active at alkaline pH, are required for industrial applications. Although a lot of information is available about the ability of fungi and bacteria to produce α-L-rhamnosidases and β-D-glucosidases as well as their catalytic properties and gene sequence [19], there are few reports on the production and characterization of these alkaline enzymes from fungi, including those associated with extreme environments [6,[20][21][22]. An example of this kind of environments is the native xerophilic forest dominated by the tree species Celtis tala Gill ex Planch (Ulmaceae) and Scutia buxifolia Reiss (Rhamnaceae) [23], and Distichlis spicata (L.) Greene grassland associated located in the eastern part of the Buenos Aires province (Argentina).…”