Solubilization of phosphate rocks and minerals by a wild-type strain and two UV-induced mutants of Penicillium rugulosum

https://doi.org/10.1016/S0038-0717(01)00099-2Get rights and content

Abstract

Two Venezuelan phosphate rocks (PRs), apatite deposits from Monte-Fresco and Navay areas, and two minerals, Florida apatite and Utah variscite were used to investigate phosphate solubilization by the wild type strain IR-94MF1 of Penicillium rugulosum initially selected for its high mineral phosphate activity (Mps+) and two of its mutants Mps++ and Mps. In liquid cultures, the three fungal strains showed better growth on the Navay PR than on Monte Fresco PR. The Utah variscite was the best phosphorus (P) source for the growth of the wild type and the Mps++ mutant. Solubilization of the various P sources by the wild-type IR-94MF1 and the Mps++ mutant resulted mostly from the action of organic acids. Citric acid seemed to be more active agent for the solubilization of the Utah variscite while gluconic acid appeared to be responsible for the solubilization of the Florida apatite and the Monte Fresco PR. Both organic acids are likely involved in the solubilization of the Navay PR. The Mps- mutant did not produce any organic acid when grown on all the P sources used.

Introduction

In South America, phosphate rocks (PRs) should provide a cheap source of phosphorus (P) fertilizer for crop production. However, most PR deposits have low reactivity (León et al., 1986) and cannot be used successfully as P sources for crop production (Kpomblekou and Tabatabai, 1994). It has been shown that organic acids can greatly increase the concentration of P in soil solution through chelation and an exchange reaction (Gadd, 1999). Therefore, the application of P solubilizing microorganisms (Kucey et al., 1989, Muchovej et al., 1989) is a promising approach for increasing P availability in PR amended soils. Production of carboxylic acids like citric and oxalic acids was associated with calcium phosphate solubilization by Penicillium bilaii (Cunningham and Kuiack, 1992). Gluconic acid was implicated in the solubilization of a rock phosphate by Penicillium variabile P16 (Vassilev et al., 1996), the solubilization of Ca and Al phosphate minerals by Penicillium radicum (Whitelaw et al., 1999), and the release of Ca2+, Al3+ and Fe3+ from rock samples by Penicillium frequentas (De La Torre et al., 1993). However, the release of toxic concentrations of some metals during PR solubilization can affect fungal growth, physiology and metabolism (Karamushka et al., 1996). We have previously described Penicillium rugulosum IR-94MF1 which was isolated from a Venezuelan soil and selected for its high mineral phosphate solubilization activity (Mps+) with hydroxyapatite, and two of its UV-induced mutants with very high (Mps++) or negative (Mps) activity (Reyes et al., 1999b). These mutants allowed the elucidation of the mechanisms of action involved in the Mps+ activity of isolate IR-94MF1. The Mps+ phenotype was mainly associated with the production of gluconic and citric acids, and it responded differently to calcium, iron and aluminum phosphate salts when used as P-sources and to ammonium, nitrate or arginine as nitrogen sources (Reyes et al., 1999a). Our long-term aim is the bioactivation of poorly soluble PR using P. rugulosum IR-94MF1. In this paper, we evaluated the solubilizing activity of IR-94MF1 on two sedimentary PR apatites obtained from the Monte Fresco and San Joaquin de Navay deposits in the southwest region of Venezuela. The activity of IR-94MF1 (isolated from a soil in contact with the Monte Fresco deposit) on the two Venezuelan PRs was also compared with its activity on an apatite mineral from Florida. As IR-94MF1 was also able to dissolve AlPO4 (Reyes et al., 1999b) we further investigated its effect on a variscite mineral from Utah.

Section snippets

Materials and methods

Four forms of P were used: two Venezuelan PRs, apatite deposits, from Monte-Fresco and Navay areas; and two minerals, Florida apatite and Utah variscite (Ward's Natural Science Establishment, Rochester, NY). All the P sources were finely ground (100% through a 100-mesh Tyler screen, 0.149-mm opening) prior to use. Following digestion in HNO3/HClO4, the amount of P was determined by the vanado-molybdate method (Tandon et al., 1968), and Ca, Mg, Na, K, Mn, Fe, Cu, Al and Zn were determined by

Results and discussion

The chemical composition of the four phosphate materials used is presented in Table 1, Table 2. The total P contents ranged from 93 to 128 mg P g−1. Florida apatite and Utah variscite contained higher amounts of P than Navay and Monte-Fresco apatites. Utah variscite contained lower amounts of Ca and higher amounts of Al and Fe as compared to other phosphate materials. The solubility of P in the phosphate materials, expressed as percentage of total P soluble in 2% citric acid and 2% formic acid,

Acknowledgements

Authors are grateful to Dr R. R. Simard for the use of his laboratory for the organic acids determinations, and to Professors M. Cescas and M. Caillier for their constructive comments. We Thank Dr Les Barran for proof reading the manuscript. I. Reyes was the recipient of a doctoral fellowship from the Venezuelan Council for Science and Technology (CONICIT) and Táchira National Experimental University (UNET) of Venezuela.

References (22)

  • J.R De Freitas et al.

    Phosphate-solubilizing rhizobacteria enhance the growth and yield but not phosphorus uptake of canola (Brassica napus L.)

    Biology and Fertility of Soils

    (1997)
  • Cited by (74)

    • Efficient bioimmobilization of cadmium contamination in phosphate mining wastelands by the phosphate solubilizing fungus Penicillium oxalicum ZP6

      2022, Biochemical Engineering Journal
      Citation Excerpt :

      Fig. 4b shows the changes in the soil soluble phosphate content during incubation. Compared with the uninoculated control group, the content of soluble phosphate in inoculated soil increased significantly because strain ZP6 produced a significant quantity of organic acids, which solubilized PR in the soil, thus releasing soluble phosphate [26,35]. However, a slight increase in soluble phosphate was observed in the soil that was not inoculated with strain ZP6.

    • Phosphate solubilization by microorganisms

      2022, New and Future Developments in Microbial Biotechnology and Bioengineering: Sustainable Agriculture: Microorganisms as Biostimulants
    • The prospects of bio-fertilizer technology for productive and sustainable agricultural growth

      2019, New and Future Developments in Microbial Biotechnology and Bioengineering: Microbial Biotechnology in Agro-environmental Sustainability
    View all citing articles on Scopus
    View full text