Mercury — Mycolyse

Until recently, it was assumed that only bacteria and algae possessed the merB operon exploited during the enzymatic reduction of methylmercury to the volatile, less toxic form Hg(0), but recent investigations into horizontal gene transfer events in fungi have potentially identified transmission of MerB. An alkylmercury lyase discovered in Metarhizium robertsii shows synonymous functionality with the operationally characterised bacterial MeHg demethylase MerB. To determine whether the protein retained its inherited function, researchers ran gene expression trials on the model organism Escherichia coli, finding that Hg resistance was indeed increased in the bacteria, as well as confirming that the purified protein removed the methyl group from MeHg to produce Hg2+. MerB works in concert with a mercury ion reductase, MerA, to achieve mercury resistance. Resistance to mercury is made possible by three components of microbial physiology:

A permeable barrier (phospholipid bilayer) that limits mercury uptake.
The production of chelating agents (thiols) that facilitate mercury sequestration, thereby limiting its bioavailability.
Biovolatilization, which involves the reduction of Hg(II) to volatile Hg(0) through an inducible mercuric ion reductase coded by the mer operon.

While this enzymatic machinery is well-documented in bacteria and algae, the discovery of methylmercury demethylase in fungi is particularly significant because the symbiotic partnerships formed between plants and certain fungi are simultaneously protective and enriching, meaning remediation strategies that can employ living fungal biomass present restorative opportunities beyond Heavy metal removal. Fungi can expand a plant’s access to nutrients, increase growth traits across the plant body, assist in pathogen and predation defense, and limit the uptake and accumulation of foreign agents, including heavy metals within plant tissues. Additionally, the support offered by symbionts stimulates microbial activity and nutrient balance in the rhizosphere. These routine charges carried out by fungi, taken in conjunction with their successful remediation activities could serve not only to ameliorate the toxicities of contaminants but provide stable and robust restoration for the extended plant and microbial populations. Studies have already accessed the viability of Hg-tolerant fungi in the remediation of Mercury from soil and the beneficial interactions between plants and fungi under mercury stress. These studies have demonstrated the protective abilities of fungi containing both demethylase and mercury ion reductase features (Penicillium spp., DC-F11 & Metarhizium robertsii) Hg-contaminated soils, as evidenced by plant root count, plant height, and fungal colony forming units.

Fungal Strain	Capacity	pH	Time	Viability	Remediation type	Application/Process	References
Saccharomyces cerevisiae	80%	6.5	72h	Immobilised	Biosorption	Milk	Massoud et al 2020
Saccharomyces cerevisiae	99.4%	5	24h	Viable	Biosorption	Batch experiments	Hadiani et al 2018
Mucor hiemalis	99%	7	48h	Immobilised	Biosorption	Batch experiments	Hoque & Fritscher 2019
Aspergillus niger	80 %	5.3	7d	Viable	volatilization Bioaccumulation	Contaminated soil	Urik et al 2014
C. cladosporioides	80%	4.3	7d	Viable	volatilization	Contaminated soil	Urik et al 2014
Penicillium canescens	54.8 mg/g	5	6h	immobilised	Adsorption	Batch experiments	say et al 2003
Aspergillus niger	83.2%	5.5	24h	immobilised	biosorption	Iron Oxide-Coated Biomass
Penicillium oxalicum	270 mg/g	6.2	24h	Immobilised	Biosorption	Batch experiments	Svecova et al 2006
Penicillium purpurogenum	70.4 mg/g	5	4h	immobilised	Biosorption	Batch experiments	Say et al 2002
Aspergillus flavus	95.6%	7	30m	Immobilised	Biosorption	Batch experiments	Mahmoud et al 2017
Lecythophora sp.KJ957772	86.8%	N/A	24h	Viable	volatilization	Fungus & biochar combination	Chang et al 2019
Aspergillus niger	95%	N/A	5d	Immobilised	Adsorption Immobilisation	Amalgamation/ WHBC + biomass of A. niger	Narayanan et al 2021
Zygosaccharomyces bailii	93.3%	N/A	14d	Immobilised	Biosorption	Kombucha	et al 2020
Coprinus micaceus	100%	5	2h	Immobilised	Biosorption	Fe2O3 magnetic nanoparticle.	Özdemir et al 2019
Penicillium spp. DC-F11	84%	N/A	7d	Viable	adsorption Precipitation	Batch experiments	Chang et al 2020
Lactarius acerrimus	95%	5	2h	Viable	Biosorption	Batch experiments	Naeemullah et al 2020

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Massoud, Ramona AU - Sharifan, Anoosheh AU - Khosravi, Kianoush AU - Asadi, GholamHassan PY - 2020/11/11 SP - T1 - Mercury biosorption process by using Saccharomyces cerevisiae in milk VL - 45 DO - 10.1111/jfpp.15008 JO - Journal of Food Processing and Preservation ER -
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