Enhanced solubilization of iron and calcium phosphates by Aspergillus niger by the addition of alcohols

The present study deals with the effect of increased concentrations of alcohols (methanol and ethanol) on the solubilization of FePO4 and CaHPO4 by Aspergillus niger. The efficiency of solubilization (ES) of inorganic phosphates, fungal growth, acid production and pH variation were determined. The concentrations of alcohols that most favored the solubilization of phosphates were 4% methanol and 3% ethanol. The ES of phosphates by the fungus in media containing methanol ranged from 11-96% and 0.4-87% for ethanol. The stimulation or inhibition of solubilization was dependent on greater or lesser fungus growth, acid production and decreased pH. These responses were supported by the correlation between the amount of phosphate dissolved and fungal growth (0.630** to 0.831**), the production of acids (0.529* to 0.989**) and a decrease in pH (-0.755** to -0.962**). Thus, the addition of alcohols facilitated insoluble phosphates dissolution during the fungus growth.

Solubilization of CaHPO4 and AlPO4 by Aspergillus niger in culture media with different carbon and nitrogen sources

The solubilization of inorganic phosphates by microorganisms supplies phosphates for plant nutrition and increases their growth. The solubilization of CaHPO4 (Ca-P) and AlPO4 (Al-P) by Aspergillus niger using several carbon and nitrogen sources was studied. Solubilization of Ca-P was enhanced when the carbon sources were mannitol, maltose, galactose and glucose (in that order). Galactose, sucrose and maltose were the carbon sources that enhanced the solubilization of Al-P. More extensive growth, acid production, and decrease in pH were obtained in the Al-P medium than in the Ca-P medium, however, the quantity of solubilized phosphate was 12 percent less. Phosphate solubilization was related to acid production, pH drop and fungal growth in the culture medium. The results of a study carried out under abiotic conditions showed that organic acids solubilize more Ca-P than Al-P. Evaluating the effect of the nitrogen source, the solubilization of Ca-P or Al-P decreased in the following order: glycine > NH4Cl > NaNO3 and NH4NO3 > urea > (NH4)2SO4, respectively. Ammoniacal nitrogen (NH4+-N) sources were the most effective in the production of acids and in lowering of the pH.

A solubilização de fosfatos inorgânicos por microrganismos disponibiliza fosfato para a nutrição das plantas e aumenta seu crescimento. A solubilização de CaHPO4 (Ca-P) e AlPO4 (Al-P) por Aspergillus niger na presença de várias fontes de carbono e de nitrogênio foi estudada. A solubilização de Ca-P foi aumentada quando as fontes de carbono foram manitol, maltose, galactose e glicose (nesta ordem). Galactose, sacarose e maltose foram as fontes de carbono que aumentaram a solubilização de Al-P. Maior crescimento, produção de ácidos e diminuição do pH foram obtidos em meio contendo Al-P do que Ca-P, porém, a quantidade de fosfato solubilizado foi apenas 12 por cento maior. A solubilização dos fosfatos foi relacionada à produção de ácidos, diminuição do pH e crescimento do fungo no meio de cultura. Resultados de um estudo conduzido sob condições abióticas mostraram que os ácidos orgânicos solubilizaram mais Ca-P do que Al-P. Avaliando-se o efeito da fonte de N, a solubilização de Ca-P ou Al-P decresceu na seguinte ordem: glicina > NH4Cl > NaNO3 ou NH4NO3 > Uréia > (NH4)2SO4, respectivamente. As fontes de N amoniacal (NH4+-N) foram as mais efetivas na produção de ácidos e diminuição do pH.