Isolation and Characterization of Environmental Bacteria Capable of Extracellular Biosorption of Mercury

Abstract

Accumulation of toxic metals in the environment represents a public health and wildlife concern. Bacteria resistant to toxic metals constitute an attractive biomass for the development of systems to decontaminate soils, sediments, or waters. In particular, biosorption of metals within the bacterial cell wall or secreted extracellular polymeric substances (EPS) is an emerging process for the bioremediation of contaminated water. Here the isolation of bacteria from soil, effluents, and river sediments contaminated with toxic metals permitted the selection of seven bacterial isolates tolerant to mercury and associated with a mucoid phenotype indicative of the production of EPS. Inductively coupled plasma-optical emission spectroscopy and transmission electron microscopy in conjunction with X-ray energy dispersive spectrometry revealed that bacteria incubated in the presence of HgCl 2 sequestered mercury extracellularly as spherical or amorphous deposits. Killed bacterial biomass incubated in the presence of HgCl 2 also generated spherical extracellular mercury deposits, with a sequestration capacity (40 to 120 mg mercury per g [dry weight] of biomass) superior to that of live bacteria (1 to 2 mg mercury per g [dry weight] of biomass). The seven strains were shown to produce EPS, which were characterized by Fourier transform-infrared (FT-IR) spectroscopy and chemical analysis of neutral-carbohydrate, uronic acid, and protein contents. The results highlight the high potential of Hg-tolerant bacteria for applications in the bioremediation of mercury through biosorption onto the biomass surface or secreted EPS.T hroughout the twentieth century, human activities such as mining, chemical industries, and agriculture have yielded high accumulations of toxic metals in the environment. These metals, bioavailable and persistent (33), constitute a major environmental problem, adversely affecting ecosystems and public health (24). Mercury pollution is of real concern because of the high toxicity of the metal and its translocation all along the food chain: mercury is accumulated upward through the aquatic food chain and is transformed to more-toxic organic mercury forms, mainly highly neurotoxic methylmercury (24).Toxic metals are difficult to remove from the environment, since they cannot be chemically or biologically degraded and are ultimately indestructible. Physicochemical remediation of metalpolluted sites, from incineration of soils to chemical precipitation or/and ion-exchange technologies, has been widely used but remains costly and environmentally damaging. Biological approaches based on metal-resistant microorganisms have received a great deal of attention as alternative remediation processes (20,26). The biological methods used currently for mercury removal consist of Hg 2ϩ reduction to volatile metal mercury by bacterial strains harboring the mer resistance operon (1,32,35,48). Live or dead bacterial biomass has also been used for biosorption applications (52), which consist of passive immobilization of metals by th...

Mineralogical Diversity in Lake Pavin: Connections with Water Column Chemistry and Biomineralization Processes

“…Based on EDXS analyses, these nanoparticles exhibited an Hg/S atomic ratio close to one, suggesting they consisted of HgS. A diversity of bacteria from various contaminated sites has been shown to sorb mercury at their surface and within extracellular polymeric substances in the form of nanometric spherical precipitates comparable to our observations [92]. In addition, sulfate-reducing bacteria may contribute to HgS precipitation through sulfide production [93].…”

Formation of manganese phosphate and manganese carbonate during long-term sorption of Mn2+by viable Shewanella putrefaciens: effects of contact time and temperature

“…The presence of the latter can be concluded from the changes in the bands near 1060 and 580 cm À1 . 28,29 More detailed study of this spectral region shows that the biosynthesis of the polymeric carbohydrates decreases as temperature increases and is practically absent at 30 C (in 30 days).…”

Biosorptive Performance of Bacillus arsenicus MTCC 4380 Biofilm Supported on Sawdust/MnFe2O4 Composite for the Removal of As(III) and As(V)

“…Tables S6 and S7 of the Electronic Supplementary Material also exhibit the intense bands at 1470.388 cm −1 which shifted to 1459.845 cm −1 (As(III)) and at 1527.442 cm −1 , shifted to 1517.727 cm −1 (As(V)) that indicated the responsibility of aromatic -NO 2 group for the biosorption/bioaccumulation process, respectively. Another shift was detected from 1449.922 to 1442.516 cm −1 (As(III)) and from 1442.516 to 1430.945 cm −1 (As(V)), corresponding to the complexation of nitrogen with As(III) and As(V) ions of the N-H group [65]. Wavenumber shifted from 1366.822 to 1375.018 cm −1 (As(III)) and from 1375.018 to 1382.326 cm −1 (As(V)) assigned the reactivity of carboxylate anion C=O stretching for the biosorption/ bioaccumulation process [53].…”