Evaluation of metal toxicity by a modified method based on the fungus Gerronema viridilucens bioluminescence in agar medium

Abstract

Metal cation toxicity to basidiomycete fungi is poorly understood, despite its well-known importance in terrestrial ecosystems. Moreover, there is no reported methodology for the routine evaluation of metal toxicity to basidiomycetes. In the present study, we describe the development of a procedure to assess the acute toxicity of metal cations (Na(+), K(+), Li(+), Ca(2+),Mg(2+), Co(2+), Zn(2+), Ni(2+), Mn(2+), Cd(2+), and Cu(2+)) to the bioluminescent basidiomycete fungus Gerronema viridilucens. The method is based on the decrease in the intensity of bioluminescence resulting from injuries sustained by the fungus mycelium exposed to either essential or nonessential metal toxicants. The assay described herein enables us to propose a metal toxicity series to Gerronema viridilucens based on data obtained from the bioluminescence intensity (median effective concentration [EC50] values) versus metal concentration: Cd(2+) > Cu(2+) > Mn(2+) approximately Ni(2+) approximately Co(2+) > Zn(2+) > Mg(2+) > Li(+) > K(+) approximately Na(+) > Ca(2+), and to shed some light on the mechanism of toxic action of metal cations to basidiomycete fungi.

Prediction of metal cation toxicity to the bioluminescent fungus Gerronema viridilucens

“…The effect of metal cations on the BL intensity of G. viridilucens was previously reported, and their toxicity was ranked based on the EC50 F values as follows: [23]. The EC50 values obtained directly from the BL versus log (cation concentration) sigmoidal curves, namely, the total median effective concentration, EC50 T [23], were converted to EC50 F using the software MINTEQA2 to calculate the free ion fraction.…”

“…The previously described fungus-based assay procedure developed by our group was followed [23,25]. In summary, All Supplemental Data may be found in the online version of this article.…”

“…Values of log (EC50 F ) were obtained by considering only the free ion concentration, because it reflects the most bioreactive metal species [8,23,27]. Models were developed using all metal ions, without any classification (e.g., valence, hard or soft character).…”

“…Recently, a bioassay to quantify the acute toxicity of metal cations to the bioluminescent basidiomycete fungus Gerronema viridilucens has been developed [23]. The method is an adaptation from the conventional growth rate-based assay in agar medium, but using the natural bioluminescence (BL) of the fungus.…”

Bioluminescência de fungos: distribuição, função e mecanismo de emissão de luz

“…45,46 As luciferases e luciferinas conhecidas hoje são utilizadas amplamente para finalidades bioanalíticas nas áreas médica (diagnósticos e estudos pré-clínicos de patologias como infecções bacterianas, virais e câncer), biotecnológica (biossensores luminescentes) e ambiental (bioensaios/biossensores de toxicidade). 47,48 Todas estas aplicações utilizam ainda umas poucas luciferases oriundas de bactérias, fotoproteínas de celenterados, crustáceos e de vagalumes. 2 Dessa maneira, a compreensão do mecanismo e da natureza dos constituintes envolvidos no processo de emissão de luz em fungos abrirá novas perspectivas de estudos acadêmicos e aplicados.…”