Inhibition of Aspergillus niger Phosphate Solubilization by Fluoride Released from Rock Phosphate

Abstract

The simultaneous release of various chemical elements with inhibitory potential for phosphate solubilization from rock phosphate (RP) was studied in this work. Al, B, Ba, Ca, F, Fe, Mn, Mo, Na, Ni, Pb, Rb, Si, Sr, V, Zn, and Zr were released concomitantly with P during the solubilization of Araxá RP (Brazil), but only F showed inhibitory effects on the process at the concentrations detected in the growth medium. Besides P solubilization, fluoride decreased fungal growth, citric acid production, and medium acidification by Aspergillus niger. At the maximum concentration found during Araxá RP solubilization (22.9 mg F(-) per liter), fluoride decreased P solubilization by 55%. These findings show that fluoride negatively affects RP solubilization by A. niger through its inhibitory action on the fungal metabolism. Given that fluoride is a common component of RPs, the data presented here suggest that most of the microbial RP solubilization systems studied so far were probably operated under suboptimal conditions.

Biochar Enhances Aspergillus niger Rock Phosphate Solubilization by Increasing Organic Acid Production and Alleviating Fluoride Toxicity

“…As observed previously (7), a small increase in F Ϫ concentration results in a large decrease in the level of solubilized P. The decrease in RP solubilization is related to inhibitory effects of F Ϫ on A. niger metabolism, especially on citric acid production and medium acidification (7). Both of these processes were increased under the application of biochar as F Ϫ adsorbent (Table 2).…”

“…The remainder of the medium in the fermentation flask was acidified with concentrated H 2 SO 4 (95%) to pH 0.5 to 1.0 to solubilize the precipitated calcium oxalate. The acidified sample was filtered through 0.2-m membranes and used for the determination of organic acids by ultraperformance liquid chromatography-tandem MS (UPLC/MS/MS) as described previously (7). The measured oxalic acid concentrations were converted to the quantity of oxalic acid in the total volume of medium.…”

“…However, it was recently demonstrated that during the solubilization process, PSMs become exposed to various chemical elements released from the RP (7). Released fluoride (F Ϫ ) was observed to cause a strong decrease in P solubilization, suggesting that most of the microbial RP solubilization systems may operate at suboptimal conditions (7), given that fluorine is a ubiquitous element in RPs (8). Thus, it is expected that strategies to remove F Ϫ while it is released from RPs could increase the overall efficiency of RP solubilization.…”

Isolation and characterization of phosphofungi, and screening of their plant growth-promoting activities

“…The pH, low-molecular-weight organic acids, and inorganic phosphate content of the supernatant were determined (Singh 2011). Fungal cell pellets were collected and dried in an oven at 70 °C to a constant weight, to determine the dry weight of the mycelium biomass (Mendes et al 2013). The entire experiment was performed in triplicate, and the data are expressed as mean values with standard deviations.…”

Biodecomposition of Jordan Phosphorite by Phosphate-Solubilizing Fungi

“…The dissolution of different types of P-contained resources (including Ca, iron and aluminum phosphates and various sources of rock phosphate) by Aspergillus niger has been demonstrated earlier (Vassilev et al 2005;Nahas, 1996;Bojinova et al, 1997;Goenadi et al 2000;Barroso et al, 2006;Bojinova et al, 2008;Mendes et al, 2013). The amount of P solubilized in culture is also depend on the composition of the medium (carbon and nitrogen composition), medium volume, pulp density, particle size, initial pH of the medium, temperature, inoculum concentration, along with culture and sampling procedures for the solubilization of the phosphates.…”