Biological Manganese Removal by Novel Halotolerant Bacteria Isolated from River Water.

Van Khanh Nguyen,Dinh Duc Nguyen,Myung-Gyu Ha,Ho Young Kang

doi:10.3390/biom10060941

Abstract

Manganese-oxidizing bacteria have been widely investigated for bioremediation of Mn-contaminated water sources and for production of biogenic Mn oxides that have extensive applications in environmental remediation. In this study, a total of 5 Mn-resistant bacteria were isolated from river water and investigated for Mn removal. Among them, Ochrobactrum sp. NDMn-6 exhibited the highest Mn removal efficiency (99.1%). The final precipitates produced by this strain were defined as a mixture of Mn2O3, MnO2, and MnCO3. Optimal Mn-removal performance by strain NDMn-6 was obtained at a temperature range of 25–30 °C and the salinity of 0.1–0.5%. More interestingly, strain NDMn-6 could be resistant to salinities of up to 5%, revealing that this strain could be possibly applied for Mn remediation of high salinity regions or industrial saline wastewaters. This study also revealed the potential of self-detoxification mechanisms, wherein river water contaminated with Mn could be cleaned by indigenous bacteria through an appropriate biostimulation scheme.

Highlights

Manganese, which is the chemical element with the atomic number 25, is in the first transition series in the periodic T of elements
Five strains, including NDMn-1, NDMn-2, and NDMn-4 isolated from Basal salt medium (BSM) medium, and NDMn-6 and NDMn-7 isolated from Nutrient broth medium (NB) medium, were selected and maintained for the subsequent investigations
Strain NDMn-1 was the bacterium that exhibited the highest Mn removal efficiency among the bacteria grown in BSM medium (Figure 1a,b,c), whereas strain NDMn-6 was the better bacterium for Mn removal between two isolated strains from the NB medium (Figure 1d,e)

Summary

Introduction

Manganese, which is the chemical element with the atomic number 25, is in the first transition series in the periodic T of elements. Manganese is an abundant element in the Earth’s crust (0.1%), at approximately one-fiftieth the amount of iron [1]. Mn does not exist as a free element, but occurs in more than 100 natural minerals, mainly in the form of oxides, carbonates, and silicates [1,2]. Manganese has a total of eight oxidation states, including 0, +1, +2, +3, +4, +5, +6, and +7. Among them, only Mn in the +2 oxidation state Mn(II) can exist as a free ion in aqueous solutions and natural water systems. The average concentration of Mn(II) in natural freshwater has been determined to be 8 μg/L [3]

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