Metal-Fungus interaction: Review on cellular processes underlying heavy metal detoxification and synthesis of metal nanoparticles

The most adverse outcome of increasing industrialization is contamination of the ecosystem with heavy metals. Toxic heavy metals possess a deleterious effect on all forms of biota; however, they affect the microbial system directly. These heavy metals form complexes with the microbial system by forming covalent and ionic bonds and affecting them at the cellular level and biochemical and molecular levels, ultimately leading to mutation affecting the microbial population. Microbes, in turn, have developed efficient resistance mechanisms to cope with metal toxicity. This review focuses on the vital tolerance mechanisms employed by the fungus to resist the toxicity caused by heavy metals. The tolerance mechanisms have been basically categorized into biosorption, bioaccumulation, biotransformation, and efflux of metal ions. The mechanisms of tolerance to some toxic metals as copper, arsenic, zinc, cadmium, and nickel have been discussed. The article summarizes and provides a detailed illustration of the tolerance means with specific examples in each case. Exposure of metals to fungal cells leads to a response that may lead to the formation of metal nanoparticles to overcome the toxicity by immobilization in less toxic forms. Therefore, fungal-mediated green synthesis of metal nanoparticles, their mechanism of synthesis, and applications have also been discussed. An understanding of how fungus resists metal toxicity can provide insights into the development of adaption techniques and methodologies for detoxification and removal of metals from the environment

List of organisms comparing their desulfurizing efficiency in percentage removal of sulfur from literature with reference to the present study.

<p>List of organisms comparing their desulfurizing efficiency in percentage removal of sulfur from literature with reference to the present study.</p

Possible bacterial strains containing <i>dszABC</i> operon.

<p>Possible bacterial strains containing <i>dszABC</i> operon.</p

Standardization of PCR product of <i>dsz</i> genes and 16s rRNA with different annealing temperatures.

<p>The PCR products with different annealing temperature were electrophoresed in agaraose gel against 100 bp DNA ladder.</p

Differential desulfurization of dibenzothiophene by newly identified MTCC strains: Influence of Operon Array - Fig 5

<p>Chromatogram showing the DBT desulfurization after 10 days of growth with different MTCC strains (a) <i>Rhodococcus rhodochrous</i> (3552), (b) <i>Artrobacter sulfureus</i> (3332), (c) <i>Gordonia rubropertincta</i> (289) and (d) <i>Rhodococcus erythropolis</i> (3951).</p

Screening of <i>dsz</i> genes in different MTCC strains <i>Rhodococcus rhodochrous</i> (3552), <i>Artrobacter sulfureus</i> (3332), <i>Gordonia rubropertincta</i> (289) and <i>Rhodococcus erythropolis</i> (3951) enriched with DBT.

<p>The different lanes are showing the amplified products of different genes <i>dszA</i>, <i>dszB</i>, <i>dszC</i> and <i>dszD</i>.</p

Differential desulfurization of dibenzothiophene by newly identified MTCC strains: Influence of Operon Array - Fig 4

<p>HPLC graph showing the retention time of (a) DBT and (b) 2-HBP. (c) The control DBT without microorganism also shows same retention time with respect to the standard DBT without any degradation.</p

4S-Pathway of biodesulfurization of dibenzothiophene (DBT).

<p>Four enzymes (DszA, DzsB, DszC and DszD) are involved in the pathway where the first three steps catalyzed by flavin mononucleotide reduced (FMNH₂)-dependent monooxygenases, those leading to DBT-sulfoxide (DBTO), DBT-dioxide (DBTO₂) and hydroxyphenyl benzenesulfinate (HPBS), respectively. The final desulfurization step to 2-hydroxybiphenyl (2-HBP) is catalyzed by desulfinase.</p