The interactions of vanadate monomer with the mycelium of fungus Phycomyces blakesleeanus: reduction or uptake?

Abstract

The possibility of reduction of vanadate monomer in the mycelium of fungus Phycomyces blakesleeanus was investigated in this study by means of polarography. Control experiments were performed with vanadyl [V(IV)] and vanadate [V(V)] in 10 mM Hepes, pH 7.2. Addition of P. blakesleeanus mycelium resulted in disappearance of all V(IV) polarographic waves recorded in the control. This points to the uptake of all available V(IV) by the mycelium, up to 185 µmol/g, and suggests P. blakesleeanus as a potential agent in V(IV) bioremediation. Polarographic measurements of mycelium with low concentrations (0.1-1 mM) of V(V), that only allows the presence of monomer, showed that fungal mycelia removes around 27% of V(V) from the extracellular solution. Uptake was saturated at 104 ± 2 µmol/g which indicates excellent bioaccumulation capability of P. blakesleeanus. EPR, V NMR and polarographic experiments showed no indications of any measurable extracellular complexation of V(V) monomer with fungal exudates, reduction by the mycelium or adsorption to the cell wall. Therefore, in contrast to vanadium oligomers, vanadate monomer interactions with the mycelium are restricted to its transport into the fungal cell, probably by a phosphate transporter.

Decavanadate Inhibits Mycobacterial Growth More Potently Than Other Oxovanadates

“…Alternatively, these observations are consistent with a hydrophobic environment having been reported in some cases to alter composition and speciation and impact the shifting of observed signals. Combined, these studies showed convincingly that the cell wall is not responsible for reduction of vanadate (Hadzibrahimovic et al, 2017 ) and these studies also confirm that tetrameric vanadate is not able to enter the cells (Zizic et al, 2016 ) as reported in yeast as well (Crans et al, 2002 ) (Willsky et al, 1984a , b .)…”

“…These studies were very elegant and truly important, because they documented the formation of decavanadate in cells from monomeric vanadate for the first time (Willsky et al, 1984b ). Recently, Zakrzewska and Zivic reported a series of studies in fungi exploring the uptake of both vanadate and V(IV) using 51 V and EPR spectroscopy, as well as polarographic studies (Zizic et al, 2013 , 2016 ; Hadzibrahimovic et al, 2017 ). The initial 51 V NMR studies on Phycomyce blakesleeanus mycelium were supplemented with polarography, which allowed for the assignment of the signal at −535 ppm accumulating inside the fungi cells to V 1 even though the pH of the system was defined by HEPES buffer at 7.2 where V 1 generally has a peak position at a higher frequency (Zizic et al, 2016 ).…”