DBPapers

SOLUBILIZATION OF NATURAL HYDROXYAPATITE BY LACTIC ACID PRODUCING RHIZOPUS ARRHIZUS IMMOBILIZED IN POLYURETHANE FOAM

AUTHOR/S: M. VASSILEVA, D. SANCHES, D. ALTMEYER, V. BRAVO, N. VASSILEV
Sunday 1 August 2010 by Libadmin2010

10th International Multidisciplinary Scientific GeoConference - SGEM2010, www.sgem.org, SGEM2010 Conference Proceedings/ ISBN 10: 954-91818-1-2, June 20-26, 2010, Vol. 2, 773-780 pp

ABSTRACT

Biotechnological solubilization of insoluble inorganic phosphate-bearing materials is
now accepted as one of the most viable alternative to the traditional chemical
methods. Many microorganisms are capable of solubilizing phosphates although this
feature is mainly attributed to metabolites such organic acids. During the recent years,
we have developed various biotechnological schemes of P-solubilization based on citric
acid (Aspergillus niger, Yarrowia lipolytica), gluconic acid (Penicillium variabile), and
oxalic acid (white-rot fungi) producers. In this work, P-solubilization was carried out
employing the filamentous fungus Rhizopus arrhizus in polyurethane-foamimmobilized
form. Experiments were performed in shake flasks under the conditions of
five repeated-batch fermentation cycles. Hydroxyapatite (HA) was supplemented to the
fermentation medium at a concentration of 1.0 and 2.0 g/l and particle size of 40 and 60
mesh. Results showed that lactic acid produced by Rhizopus arrhizus was able to
solubilize the inorganic phosphate by its hydroxyl and carboxyl groups. The process of
solubilization depended on the size of the P-bearing particles (the lower the size the
higher the concentration of soluble P in the medium). The highest solubilization level
(percentage soluble P/total P) of 47 % was reached at the 3d batch cycle using the lower
size particles applied at concentration of 1.0 g/l. Higher concentration of soluble
phosphate was found when using 2.0 g/l of HA but the solubilization efficiency was
lower. HA was found to stimulate lactic acid production as it served as a pH corrector
during the fermentation. Similarly, the slow release of phosphate due to phosphate
solubilization enhances lactic acid production in the P-deficient production medium.

Keywords: Rhizopus arrhizus; Immobilization; Lactic acid production; Hydroxyapatite; Solubilization