Fungal
solubilization of rock phosphate on media based on agroindustrial wastes
Estacion
Experimental del Zaidin, CSIC, Prof. Albareda, 1, 18008-Granada, SPAIN
E-mail: rosario.azcon@eez.csic.es
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Apart
of the wide use of lignocellulosic materials in composting and bioconversion
processes there has been increasing interest in organic acid production based
on agroindustrial residues. As the principal mechanism for mineral phosphate
solubilization is the production of organic acids, rock phosphate (RP)
dissolution by acid-producing microorganisms grown on agrowastes is currently
accepted as a very attractive approach.
Fluorapatite
was solubilized by Aspergillus niger and Phanerochaete
chrysosporium on media containing sugar beet waste (SB), olive cake (OC, alperujo),
dry olive cake (DOC, orujo seco), and olive mill wastewaters (OMWW, alpechin).
Solubilization rate increased during the fermentation processes reaching a
maximum of 224 mg/ml (SB), 159 mg/ml (OC), 326 mg/kg (DOC), and 364 mg/ml (OMWW). A strong relationship was observed
between the medium acidification and RP solubilization activity in the case of
treatments with A. niger, while this mechanism was not well pronounced in
treatments with P. chrysosporium. The highest productivity of
10.6 mg soluble P l-1 h-1 was achieved in treatments with
immobilized cells of A. niger in repeated-batch mode of fermentation.
The
resulting fermentation products were further introduced into soil-plant
systems. Compared to other treatments, the results showed a higher plant growth
rate and shoot P concentration when A. niger-treated SB and RP were
applied to both mycorrhizal and non-mycorrhizal plants. However, combined
introduction of both the fungal-treated wastes and arbuscular mycorrhizal fungi
appeared to be highly efficient approach.
Although it is
difficult to compare and generalize the results because of difference in
substrate, soil and plant characteristics, there is no doubt that
biotechnological schemes based on RP solubilization on agroindustrial wastes
are a powerful tool in the so-called sustainable agriculture.