Subcellular distribution and chemical forms of cadmium in a dark septate endophyte (DSE), Exophiala pisciphila

Abstract

Our objective was to understand the cadmium (Cd) tolerance mechanisms by investigating the subcellular distribution, chemical forms of Cd and adsorptive groups in the mycelia of Exophiala pisciphila. We grew E. pisciphila in the liquid media with increasing Cd concentrations (0, 25, 50, 100, 200, and 400 mg L(-1)). Increased Cd in the media caused a proportional increase in the Cd uptake by E. pisciphila. Subcellular distribution indicated that 81 to 97% of Cd was associated with the cell walls. The largest amount and proportion (45-86%) of Cd was extracted with 2% acetic acid, and a concentration-dependent extraction was observed, both of which suggest that Cd-phosphate complexes were the major chemical form in E. pisciphila. A large distribution of phosphate and Cd on the mycelia surface was observed by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The precipitates associated with the mycelia were observed to contain Cd by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX). Fourier transform infrared (FTIR) identified that hydroxyl, amine, carboxyl, and phosphate groups were responsible for binding Cd. We conclude that Cd associated with cell walls and integrated with phosphate might be responsible for the tolerance of E. pisciphila to Cd.

Co-inoculation of Lolium perenne with Funneliformis mosseae and the dark septate endophyte Cadophora sp. in a trace element-polluted soil

“…DSEs, Zhan et al (2015) showed that Exophiala pisciphila could adsorb 81 to 97% of Cd onto its cell walls, but none of those previous studies was confirmed in planta or performed with another DSE (such as Cadophora sp. ).…”

Exogenous Glutathione Alleviation of Cd Toxicity in Italian Ryegrass (Lolium multiflorum) by Modulation of the Cd Absorption, Subcellular Distribution, and Chemical Form

“…Similar results were also observed in Italian ryegrass root under Cd stress, the toxicity easily appeared in Harukaze with lower TI (Table 1), which was partly supported by the significant negative correlation between the root TI and the proportion of Cd extracted by 80% ethanol (Table 4). The proportion of Cd bonded to undissolved phosphate (Cd extracted by 2% HAC) with low mobility and toxicity showed an increase in the Exophiala pisciphila mycelia root under Cd stress [51].…”

Unravelling the Role of Melanin in Cd and Zn Tolerance and Accumulation of Three Dark Septate Endophytic Species

“…and P. mustea. Other intra-or extra-cellular mechanisms must occur, including either non-enzymatic or enzymatic efficient detoxifying processes against TE-induced ROS, as reported for E. pisciphila and G. cylindrosporus [8,53]. Moreover, efflux transport systems, sequestration into vacuoles, or intracellular chelation usually represent the major components of metal tolerance in other fungi [54][55][56][57].…”

“…Moreover, efflux transport systems, sequestration into vacuoles, or intracellular chelation usually represent the major components of metal tolerance in other fungi [54][55][56][57]. Such mechanisms have also been proposed from the transcriptomic data of mycelia exposed to TE in the DSE fungi E. pisciphila and Cadophora finlandica [8,10,53]. However, the identification and the functional characterization of the genes/proteins that are involved have not yet been performed [12].…”