Characteristics of phosphate solubilization by an isolate of a tropical Penicillium rugulosum and two UV-induced mutants

Abstract

After screening several fungal isolates obtained from Venezuelan soils, the isolate IR‐94MF1 of Penicillium rugulosum was selected for its high mineral phosphate solubilizing activity (Mps+) with hydroxyapatite. Mutants with altered (Mps−) or amplified activity (Mps++) were obtained by UV irradiation of conidia. When glucose was used as the sole C source by the fungus, gluconic acid was associated with the hydroxyapatite activity. In solid media, in comparison to glucose and maltose, sucrose appeared to be the best C source for the solubilization of hydroxy‐apatite and FePO4.

Effect of nitrogen source on the solubilization of different inorganic phosphates by an isolate of Penicillium rugulosum and two UV-induced mutants

“…Although the wild‐type in the KH 2 PO 4 liquid medium presented similar growth with arginine, nitrate and nitrate+ammonium (Table 2), citric acid was produced in larger concentrations only with nitrate (12.78 mM, Table 4). However, for FePO 4 a measurable solubilizing halo was previously reported for the wild‐type isolate [17] grown in the presence of nitrate+ammonium and sucrose. Azcon et al [34] reported that under dry conditions, mycorrhizal plants produced a higher yield than phosphate fertilized plants when nitrate was supplied as the only N source, in the absence of ammonium.…”

“…When sucrose was used as the sole C source, the MPS activity was accompanied by the production of citric and gluconic acids in the culture media; however, only gluconic acid was found when glucose was used [17]. With sucrose, both acids were produced by the wild‐type and the Mps ++ mutant, but they were not detected in filtrates from the Mps − mutant (Table 3Table 4).…”

“…It is known that citric acid is able to solubilize calcium phosphate [26]. Therefore, it is suggested here that an induction of a ‘short’ path (direct oxidation of the aldonic sugar by nonphosphorylating oxidation) could be selected by IR‐94MF1 instead of a ‘long’ biosynthetic pathway [17], when HA is used as the phosphate source. This hypothesis could explain the low growth of IR‐94MF1 on this phosphate source (Table 2).…”

“…Penicillium rugulosum IR‐94MF1 is a fungus with a high hydroxyapatite (HA) solubilization capacity isolated from a pasture tropical soil present on the top of an unexploited apatite‐rock‐phosphate mine [17]. Mutants with a negative (Mps − ) or an amplified (Mps ++ ) MPS activity were developed and our results showed that P solubilization activities were significantly higher when sucrose was used as the C source as compared to glucose or maltose [17].…”

“…Inocula for the wild‐type P. rugulosum IR‐94MF1 and its mutants were prepared by using a synchronous 3‐day‐old vegetative mycelium prepared as described by Reyes et al [17].…”