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Interconnection between PHA and Stress Robustness of Bacteria
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Stanislav Obruca, Petr Sedlacek, Iva Pernicova, Adriana Kovalcik, Ivana Novackova, Eva Slaninova, Ivana Marova
The microorganisms which are able to grow with a high concentration of heavy metals are known as metallotolerants. There are no microbial strains that require the presence of heavy metals for their growth but some of their production metabolic pathways could be directly caused or at least enhanced by the presence of heavy metal ions in the solutions where cells occur. A typical example could be seen for the PHA model microorganism Cupriavidus necator when, moreover, nitrogen limitation together with an excess of a carbon source led to a higher PHB amount in cells. Also, the presence of heavy metal ions such as copper, iron or nickel led to enhanced production of PHA. The resistance against high concentrations of different heavy metals including copper, nickel, zinc, cadmium, lead, arsenic, mercury and others was described for the microbial strain Cupriavidus metallidurans CH34 isolated from the metal processing factory. All defense mechanisms were described for this strain. The resistance against heavy metals could be associated with genetic determinants occurring within plasmids, transposons or chromosomal DNA when the transfer of genes causing the resistance is used by many microorganisms as a strategy of how to survive this stress. Enzymes of the PHA biosynthetic pathway were characterized and it was observed that more copies of individual genes are located in different places in the genome in contrast with the genome of C. necator. Moreover, some of them showed dissimilarities considering the substrate specificity which could lead to the ability of utilization of different carbon sources for PHA production as well as an ability to incorporate a wider range of monomers [113–115].
Mechanisms of Bacterial Heavy Metal Resistance and Homeostasis
Published in Edgardo R. Donati, Heavy Metals in the Environment, 2018
Pallavee Srivastava, Meenal Kowshik
The RND family of transporters found in all three domains of life represent the first level of heavy metal resistance and are involved in export of superfluous cations (Nies, 2003). They were first described as a related group of bacterial transport proteins involved in heavy metal resistance (Cupriavidus metallidurans), nodulation (Mesorhizobium loti) and cell division (E. coli). RND superfamily is involved in export of heavy metals, hydrophobic compounds, amphiphiles, nodulation factors, and proteins (Nies, 2003). The CzcA (for Co2+/Zn2+/Cd2+ efflux), SilA (Ag+-specific exporter), and CusA (Cu+/Ag+ effluxer) are components of tripartite CBA-type efflux complexes responsible for metal resistance mostly in Gram-negative bacteria (Silver, 2003). The CzcA protein is encoded by the czcCBA operon (Fig. 2d), which also encodes for the CzcC, the outer membrane factor (OMF) and CzcB, the membrane fusion protein (MFP) (van der Lelie et al., 1997). RND proteins employ proton motive force to achieve cation efflux (Kim et al., 2011). The homotrimers or heterotrimers forming the RND proteins are composed of two different RND polypeptides in a 2:1 ratio (Kim et al., 2011). Each RND monomer has 12 transmembrane α-helices that span the inner membrane. The RND trimer contains a large hydrophilic portion that extends into the periplasmic space (Murakami et al., 2006), and connects to the second component of the CBA system, the trimeric OMF. The three subunits of OMF span the outer membrane as β-barrel (Koronakis et al., 2000). The MFP is periplasmic and forms a hexa/trimeric ring around the RND and the OMF to complete the CBA system (Fig. 8) (Akama et al., 2004). The active transport of heavy metals out of the cell results in decreased intracellular concentrations thereby conferring resistance.
Toxic Metal Removal Using Microbial Nanotechnology
Published in Mahendra Rai, Patrycja Golińska, Microbial Nanotechnology, 2020
Some chromate-resistant bacteria such as Pseudomonas fluorescens, Enterobacter cloacae and Acinetobacter sp. (Fig. 2.2) have been shown to remove Cr from industrial effluent (Srivastava and Thakur 2007, Thatheyus and Ramya 2016). Bacteria detoxify chromium mainly by reducing Cr(VI) to Cr(III), through Cr(V) and Cr(IV) intermediates, and it is a potentially useful process in the remediation of Cr(VI)-affected environments. Reduction of Cr(VI) to Cr(III) can be performed by various species of Pseudomonas, including Pseudomonas aeruginosa, P. synxantha, P. putida, P. ambigua, P. fluorescens, P. dechromaticans and P. chromatophila (Cheung et al. 2006). Bacteria from other genera that can reduce Cr(VI) include Acinetobacter lwoffii, Bacillus megaterium, Aeromonas dechromatica and Escherichia coli ATCC 33456 (Srivastava and Thakur 2007, Shen and Wang 1993). Sulfate-reducing bacteria Desulfovibrio desulfuricans and D. vulgaris were reported to reduce Cr(VI). Some extremophiles such as the radiation-resistant Deinococcus radiodurans and Thermoanaerobacter ethanolicus isolated from subsurface sediments reduced Cr(VI) (Fredrickson et al. 2000). Pyrobaculum islandicum was capable of reducing Cr(VI) at high temperatures (Kashefi and Lovley 2000). Resistance to Cr(VI) was investigated in Pseudomonas aeruginosa, which was attributed to the decreased uptake and/ or enhanced efflux of Cr(VI) by the cell membrane (Dogan et al. 2011). A similar resistance mechanism was reported in Cupriavidus metallidurans CH34, which was resistant to eight metals including Zn(II), Cd(II), Co(II), Ni(II), Cu(II), CrO2– 4, Hg(II), and Pb(II) (Monsieurs et al. 2011, Mergeay et al. 2003). Bacillus circulans, B. megaterium and B. coagulans exhibited efficient Cr removal but Agrobacterium radiobacter EPS-916, Microbacterium liquefaciens and Zoogloea ramigera did not (Thatheyus and Ramya 2016).
Hexavalent chromium bioremediation with insight into molecular aspect: an overview
Published in Bioremediation Journal, 2021
Sreejita Ghosh, Amrita Jasu, Rina Rani Ray
Juhnke et al. (2002) reported that Cupriavidus metallidurans strain AE126 without the chrB1 gene shows a comparatively higher chromate tolerance than the wild type strain; but a weak chromate reduction was observed in the mutant strain on removal of chrC and chrI genes. Also, in this same finding, it was reported that the chrF2 genes in Cupriavidus metallidurans strain AE126 increased the chromate reduction capability whereas removal of chrA2 and chrB2 genes extremely diminished the chromate reduction ability. In the bacterial species of Arthrobacter sp. strain FB24 removal of chrJ, chrK and chrL genes lead to a drastic decrease in the chromate reduction ability.