4.1.2 Precipitation
Precipitation is defined as the creation of insoluble inorganic metal precipitates. This
might be more simply understood when metals are attached to extracellular polymeric elements excreted by eukaryotic microorganisms, especially yeast and fungi.
The precipitates might be made and persist in contact with or inside the microbial
cells or may be independent of the compact phase of the microbial cell (Bahafid et al.
2017). Precipitation of metals outside the cell occurs on the surface of the cell and in
the solution. Precipitation is considered to be a metabolically dependent process
when the fungal cell secretes such substances that favor precipitation; else, it is
independent because no intracellular secretions are involved, and metal surface
chemical interactions induce precipitation (Shakya et al. 2015).
4.2 Intracellular Sequestration of Heavy Metals
Due to their nature of cell wall and fast growth rate, fungi reduce the environmental
pollutants into less toxic forms. This process is through metabolic activity within
living organisms (Bahobil et al. 2017) through chemical reactions such as oxidation,
reduction, methylation, and dealkylation; they can transform toxins through volatilization and reduce the metal toxicity (Siddiquee et al. 2015). They also transfer
excess metals to fungi mycelium and plant symbiosis by cytoplasmic vesicles and
vacuoles.
4.2.1 Glomalin Production
Glomalin appears to be effective in sequestering different heavy metals, particularly
Cu, Pb, and Cd found in high concentrations in polluted dust (Gonzalez-Chavez
et al. 2004). Arbuscular mycorrhizal fungi (AMF) produce glomalin, initially
believed to be a secreted hydrophobin and later identified as a spore- and cell
wall-localized 60-kilodalton heat shock protein, which looks to play a role in
heavy metal immobilization (Ferrol et al. 2016). Regardless of the possibility of
the secretion of organic acids such as chelators, glomalin, a glycoprotein exuded by
arbuscular mycorrhizal fungi, has been proposed to play a role in metal immobilization, as illustrated in Fig. 17.2 (González-Guerrero et al. 2009).
4.2.2 Molecular Homeostasis
Uptake of essential metals through the mycorrhizal pathway starts through the cell
membrane of the extraradical mycelium. Genome sequencing and transcriptomic
analyses of Rhizopus irregularis brought in the identification of various genes
364
A. Ayele et al.
Precipitation is defined as the creation of insoluble inorganic metal precipitates. This
might be more simply understood when metals are attached to extracellular polymeric elements excreted by eukaryotic microorganisms, especially yeast and fungi.
The precipitates might be made and persist in contact with or inside the microbial
cells or may be independent of the compact phase of the microbial cell (Bahafid et al.
2017). Precipitation of metals outside the cell occurs on the surface of the cell and in
the solution. Precipitation is considered to be a metabolically dependent process
when the fungal cell secretes such substances that favor precipitation; else, it is
independent because no intracellular secretions are involved, and metal surface
chemical interactions induce precipitation (Shakya et al. 2015).
4.2 Intracellular Sequestration of Heavy Metals
Due to their nature of cell wall and fast growth rate, fungi reduce the environmental
pollutants into less toxic forms. This process is through metabolic activity within
living organisms (Bahobil et al. 2017) through chemical reactions such as oxidation,
reduction, methylation, and dealkylation; they can transform toxins through volatilization and reduce the metal toxicity (Siddiquee et al. 2015). They also transfer
excess metals to fungi mycelium and plant symbiosis by cytoplasmic vesicles and
vacuoles.
4.2.1 Glomalin Production
Glomalin appears to be effective in sequestering different heavy metals, particularly
Cu, Pb, and Cd found in high concentrations in polluted dust (Gonzalez-Chavez
et al. 2004). Arbuscular mycorrhizal fungi (AMF) produce glomalin, initially
believed to be a secreted hydrophobin and later identified as a spore- and cell
wall-localized 60-kilodalton heat shock protein, which looks to play a role in
heavy metal immobilization (Ferrol et al. 2016). Regardless of the possibility of
the secretion of organic acids such as chelators, glomalin, a glycoprotein exuded by
arbuscular mycorrhizal fungi, has been proposed to play a role in metal immobilization, as illustrated in Fig. 17.2 (González-Guerrero et al. 2009).
4.2.2 Molecular Homeostasis
Uptake of essential metals through the mycorrhizal pathway starts through the cell
membrane of the extraradical mycelium. Genome sequencing and transcriptomic
analyses of Rhizopus irregularis brought in the identification of various genes
364
A. Ayele et al.