A Biotechnological Process for Valorizing Poultry Feathers through Keratinolytic Cladosporium Isolates ^†

Protein hydrolysates, as plant biostimulants, have beneficial effects on the growth, yield and quality of agricultural crops [1,2]. A good and available source of protein hydrolysates are keratin wastes from the agro-industry, especially from the poultry industry. Isolation and characterization of keratin-degrading microorganisms with keratinolytic activity and plant growth-promoting activity represent a biotechnological approach for valorizing poultry feathers. In the present study, three keratinolytic Cladosporium isolates were investigated for their potential as plant growth promotion agents.

Qualitative tests for production of several secondary metabolites were carried out in Petri plates on solid specific medium [3,4]. In some tests, the response was estimated by measuring the diameter of the clear zone formed around the inoculation point in solid media. The following tests were carried out: production of phytohormone, namely 3-indole acetic acid (medium with tryptophan), secretion of hydrolytic enzymes, zinc solubilization (medium with insoluble zinc compounds), phosphate solubilization (medium with Ca₃(PO₄)₂ and brom cresol purple as pH indicator).

Relevant characteristics for use as a plant growth promoting were evidenced in Cladosporium sp. T2 which presented a good production of 3-indole acetic acid, a common plant hormone, responsible for various aspects of plant growth and development. Moreover, Cladosporium isolate T2 had the ability to secrete lytic enzymes (e.g., chitinases, cellulases, keratinases, proteases), a relevant feature for plant biostimulants. The isolate T2 was active in zinc solubilization, an imperative micronutrient for plant growth. The ability for phosphate solubilization has significance through increasingthe bioavailability of insoluble phosphorus from soil to be used by plants.

Members of the Cladosporium genus, endophytic fungi in a special relationship with plant hosts, have a great potential to improve plant growth and tolerance to abiotic and biotic stresses. In addition to this general behavior of the genus, the experimental results indicated that the selected Cladosporium isolate T2 presents relevant features as a plant biostimulant. Further study will be focused on the effect produced on plants by treatment with feather hydrolysates.