Microbiologia
URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/11840
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Item Mechanisms of phosphate solubilization by fungal isolates when exposed to different P sources(Annals of Microbiology, 2014-03) Mendes, Gilberto de Oliveira; Freitas, André Luiz Moreira de; Pereira, Olinto Liparini; Silva, Ivo Ribeiro da; Vassilev, Nikolay Bojkov; Costa, Maurício DutraThe use of phosphate-solubilizing fungi is a promising biotechnological strategy in the management of phosphorus (P) fertilization, as it enables the utilization of rock phosphates (RP) or the recovery of P fixed in soil particles. The objective of our study was to evaluate fungal isolates for mechanisms of solubilization of P-bearing compounds, such as AlPO4, FePO4, Ca3(PO4)2, Araxá RP, and Catalão RP. Four fungal isolates obtained from Brazilian soils were characterized in liquid media: Aspergillus niger FS1, Penicillium canescens FS23, Eupenicillium ludwigii FS27, and Penicillium islandicum FS30. A. niger FS1 was the only isolate able to solubilize all of the P sources, solubilizing 71, 36, 100, and 14 % of the P from AlPO4, FePO4, Ca3(PO4)2, and RPs, respectively. Medium acidification was an effective solubilization mechanism, particularly for Ca3(PO4)2. The other P sources were mainly solubilized through organic acids produced by the fungi. Oxalic acid, produced exclusively by A. niger FS1, and citric acid were decisive factors in the solubilization of AlPO4 and FePO4. Penicillium isolates produced more gluconic acid than A. niger FS1 in all treatments. However, this higher production did not result in higher solubilization for any of the P sources, showing that gluconic acid contributes little to the solubilization of the P sources evaluated. The higher capacity of medium acidification and the production of organic acids with stronger metal-complexation activity are characteristics that confer to A. niger FS1 a wider action on insoluble P sources. Consequently, this isolate qualifies as a promising candidate for application in the management of P fertilization.Item Decreased mineral availability enhances rock phosphate solubilization efficiency in Aspergillus niger(Annals of Microbiology, 2014-05-30) Oliveira, Samantha Caixeta de; Mendes, Gilberto de Oliveira; Silva, Ubiana Cássia da; Silva, Ivo Ribeiro da; Ribeiro Júnior, José Ivo; Costa, Maurício DutraMicrobial solubilization of rock phosphate (RP) is mainly achieved by the production of organic acids and medium acidification through H+ release. During RP solubilization, mineral nutrient availability is likely to be critical for determining how much carbon is channeled either for metabolite synthesis or for microbial growth, influencing organic acid release by microorganisms. Thus, the objective of this work was to study the relationships between the concentration of mineral nutrients in the growth medium and the efficiency of RP solubilization by Aspergillus niger FS1. For this, the fungus was grown in Czapek medium containing 0, 1, 2, 10, 50, and 100 % of its original concentration of mineral nutrients. Decreasing mineral availability in the growth medium led to decreases in fungal biomass and solubilized P, and increases in titratable acidity and solubilization efficiency as expressed by mg solubilized P per g fungal biomass (YP/B), indicating a shift in fungal metabolism from biomass production to organic acid release. The transfer of pre-grown biomass to media with or without added minerals confirmed that lower mineral availability increases YP/B and led to the solubilization of 76 % of P present in Patos RP. These observations open new perspectives on improving RP solubilization systems by manipulating mineral nutrient availability in the medium, with consequent gains in cost reduction.