Mechanisms of bacterial resistance to chromium compounds

Abstract

Chromium is a non-essential and well-known toxic metal for microorganisms and plants. The widespread industrial use of this heavy metal has caused it to be considered as a serious environmental pollutant. Chromium exists in nature as two main species, the trivalent form, Cr(III), which is relatively innocuous, and the hexavalent form, Cr(VI), considered a more toxic species. At the intracellular level, however, Cr(III) seems to be responsible for most toxic effects of chromium. Cr(VI) is usually present as the oxyanion chromate. Inhibition of sulfate membrane transport and oxidative damage to biomolecules are associated with the toxic effects of chromate in bacteria. Several bacterial mechanisms of resistance to chromate have been reported. The best characterized mechanisms comprise efflux of chromate ions from the cell cytoplasm and reduction of Cr(VI) to Cr(III). Chromate efflux by the ChrA transporter has been established in Pseudomonas aeruginosa and Cupriavidus metallidurans (formerly Alcaligenes eutrophus) and consists of an energy-dependent process driven by the membrane potential. The CHR protein family, which includes putative ChrA orthologs, currently contains about 135 sequences from all three domains of life. Chromate reduction is carried out by chromate reductases from diverse bacterial species generating Cr(III) that may be detoxified by other mechanisms. Most characterized enzymes belong to the widespread NAD(P)H-dependent flavoprotein family of reductases. Several examples of bacterial systems protecting from the oxidative stress caused by chromate have been described. Other mechanisms of bacterial resistance to chromate involve the expression of components of the machinery for repair of DNA damage, and systems related to the homeostasis of iron and sulfur.

Isolation and Characterization of Chromium(VI)-Reducing Bacteria from Tannery Effluents

“…Chromate tolerance mechanisms in bacteria have been reported to include reduction, methylation, precipitation at the cell surface, blocking cellular uptake by altering the uptake pathway and removal from the cytoplasm by efflux pumps [19][20][21]. In the present study the mechanism of chromate tolerance was not investigated.…”

Development of a Novel Electrochemical Inhibition Sensor Array Based on Bacteria Immobilized on Modified Screen-Printed Gold Electrodes for Water Pollution Detection

“…For this work the following three types of bacteria were selected: (i) Escherichia coli (E. coli, K12 strain) which belong to gram-negative bacteria type generally sensitive to different types of pollutants including heavy metals, pesticides, and hydrocarbons [16], (ii) Shewanella oneidensis (S. oneidensis, MR-1 strain) which belong to gram-positive bacteria and known to be tolerant to heavy metals [17] because of its bio-catalytic-activity towards heavy metals [25], and (iii) Methanotrophic bacteria (Methylococcus capsulatus, Bath strain) gramnegative bacteria which thrive in the presence of some petrochemicals [18][19] because of its bio-degradation-properties [27]. LB (Luria-Bertain) broth was used as a medium for E. coli [20] and S. oniedensis bacterial cell cultures, while M. capsulatus were grown in NMS (Nitrate Mineral Salts) medium [21].…”

Reduction of chromium (VI) compounds by sulfate-reducing bacteria

“…Сполуки п'яти-(Cr (V), чотири-(Cr (IV) і двовалентного (Cr (IІ) хрому нестабільні й у природі трап ляються рідко [27]. Токсична дія хрому (ІІІ) пов'язана з його здатністю заміщувати магній у ДНК полімеразі та в інших ферментах, зв'язуватися з PO 4 3--групами, реагувати з карбо-нільними і сульфгідрильними групами ферментів, впливати на процеси реплікації і транскрипції [12,40,42,49]. Cr (VI) може викликати перфорацію носової перего-родки, астму, бронхіт, запалення легень і печінки, рак бронхів.…”