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Review
. 2021 Jan 28:11:619766.
doi: 10.3389/fmicb.2020.619766. eCollection 2020.

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

Zeeshanur Rahman  1 , Lebin Thomas  2
Affiliations
Review

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

Zeeshanur Rahman et al. Front Microbiol. .

Abstract

Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of different external organic and inorganic substances as electron donors to promote Cr(VI) reduction process by different microorganisms. The use of various redox mediators enabled electron transport facility for extracellular Cr(VI) reduction and accelerated the reaction. Also, many chemicals have employed diverse roles to improve the Cr(VI) reduction process in different microorganisms. The application of aforementioned materials at the contaminated systems has offered a variety of influence on Cr(VI) bioremediation by altering microbial community structures and functions and redox environment. The collective insights suggest that the knowledge of appropriate implementation of suitable nutrients can strongly inspire the Cr(VI) reduction rate and efficiency. However, a comprehensive information on such substances and their roles and biochemical pathways in different microorganisms remains elusive. In this regard, our review sheds light on the contributions of various chemicals as electron donors, redox mediators, cofactors, etc., on microbial Cr(VI) reduction for enhanced treatment practices.

Keywords: Cr(VI) reduction; chemical-assisted; electron donors; electron mediators; microbially mediated process.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Role of various chemicals other than electron donors and mediators on enhanced Cr(VI) reduction.
FIGURE 2
FIGURE 2
The general mechanisms of chemical-assisted microbially mediated Cr(VI) reduction.
FIGURE 3
FIGURE 3
The utilization of various electron donors for Cr(VI) reduction. EVO and ETS mean emulsified vegetable oil and electron transport system, respectively. Sign represents assimilation.
FIGURE 4
FIGURE 4
Different pathways for accelerated Cr(VI) reduction using different electron mediators.
See this image and copyright information in PMC

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