Characterization of Fe (III)-reducing enrichment culture and isolation of Fe (III)-reducing bacterium Enterobacter sp. L6 from marine sediment

Iron reducing sludge as a source of electroactive bacteria: assessing iron reduction in biofilm bacteria, planktonic cells and isolates from a microbial fuel cell

In this study, bacteria from a microbial fuel cell (MFC) and isolates were evaluated on their Fe³⁺ reduction capability at different concentrations of iron using acetate as the sole source of carbon. The results demonstrated that the planktonic cells can reach an iron reduction up to 60% at 27 mmol Fe³⁺. Azospira oryzae (µ 0.89 ± 0.27 d^-1) and Cupriavidus metallidurans CH34 (µ 2.34 ± 0.81 d^-1) presented 55 and 62% of Fe³⁺ reduction, respectively, at 16 mmol l^-1. Enterobacter bugandensis (µ 0.4 ± 0.01 d^-1) 40% Fe³⁺ at 27 mmol l^-1, Citrobacter freundii ATCC 8090 (µ 0.23 ± 0.05 d^-1) and Citrobacter murliniae CDC2970-59 (µ 0.34 ± 0.02 d^-1) reduced Fe³⁺ in ~ 50%, at 55 mmol l^-1. This is the first report on these bacteria on a percentage of iron reduction. These results may be useful for anode design to contribute to a higher energy generation in MFCs.

Generation of electrical energy in a microbial fuel cell coupling acetate oxidation to Fe3+ reduction and isolation of the involved bacteria

An iron reducing enrichment was obtained from sulfate reducing sludge and was evaluated on the capability of reducing Fe³⁺ coupled to acetate oxidation in a microbial fuel cell (MFC). Three molar ratios for acetate/Fe³⁺ were evaluated (2/16, 3.4/27 and 6.9/55 mM). The percentages of Fe³⁺ reduction were in a range of 80-90, 60-70 and 40-50% for the MFCs at closed circuit for the molar ratios of 2/16, 3.4/27 and 6.9/55 mM, respectively. Acetate consumption was in a range of 80-90% in all cases. The results obtained at closed circuit for current density were: 11.37 mA/m², 4.5 mA/m² and 7.37 mA/m² for the molar ratios of 2/16, 3.4/27 and 6.9/55 mM, respectively. Some microorganisms that were isolated and identified in the MFCs were Azospira oryzae, Cupriavidus metallidurans CH34, Enterobacter bugandensis 247BMC, Citrobacter freundii ATCC8090 and Citrobacter murliniae CDC2970-59, these bacteria have been reported as exoelectrogens in MFC and in MFC involving metals removal but not all of them have been reported to utilize acetate as preferred substrate. The results demonstrate that the isolates can utilize acetate as the sole source of carbon and suggest that Fe³⁺ reduction was carried out by a combination of different mechanisms (direct contact and redox mediators) utilized by the bacteria identified in the MFC. Storage of the energy generated from the 2/16 mM MFC system arranged in a series of three demonstrated that it is possible to utilize the energy to charge a battery.

Assessment of the tolerance to Fe, Cu and Zn of a sulfidogenic sludge generated from hydrothermal vents sediments as a basis for its application on metals precipitation

A paramour factor limiting metal-microorganism interaction is the metal ion concentration, and the metal precipitation efficiency driven by microorganisms is sensitive to metal ion concentration. The aim of the work was to determine the tolerance of the sulfidogenic sludge generated from hydrothermal vent sediments at microcosms level to different concentrations of Fe, Cu and Zn and the effect on the microbial community. In this study the chemical oxygen demand (COD) removal, sulfate-reducing activity (SRA) determination, inhibition effect through the determination of IC₅₀, and the characterization of the bacterial community´s diversity were conducted. The IC₅₀ on SRA was 34 and 81 mg/L for Zn and Cu, respectively. The highest sulfide concentration (H₂S mg/L) and % of sulfate reduction obtained were: 511.30 ± 0.75 and 35.34 ± 0.51 for 50 mg/L of Fe, 482.48 ± 6.40 and 33.35 ± 0.44 for 10 mg/L of Cu, 442.26 ± 17.1 and 30.57 ± 1.18 for 10 mg/L of Zn, respectively. The COD removal rates were of 71.81 ± 7.6, 53.92 ± 1.07 and 57.68 ± 10.2 mg COD/ L d for Fe (50 mg/L), Cu (40 mg/L) and Zn (20 mg/L), respectively. Proteobacteria, Firmicutes, Chloroflexi and Actinobacteria were common phyla to four microcosms (stabilized sulfidogenic and added with Fe, Cu or Zn). The dsrA genes of Desulfotomaculum acetoxidans, Desulfotomaculum gibsoniae and Desulfovibrio desulfuricans were expressed in the microcosms supporting the SRA results. The consortia could be explored for ex-situ bioremediation purposes in the presence of the metals tested in this work.

Isolation and characterization of an acid and metal tolerant Enterobacter cloacae NZS strain from former mining lake in Selangor, Malaysia

Background

Metal polluted environments have been found to harbor acid and metal tolerant bacterial communities. Metal oxidizing bacteria in particular are industrially important microorganisms that can be utilized for potential applications in biomining and bioremediation. However, some well-characterized strains are not readily culturable as they are obligate and fastidious chemolithotrophs requiring special techniques for their cultivation. Hence, this study was aimed at isolating, identifying, and characterizing indigenous metal tolerant heterotroph(s) from abandoned mines that can potentially be used for biomining or bioremediation processes in the future.

Results

Seventeen bacteria from former mining lakes were isolated and identified using 16S rRNA. Minimal inhibition concentration (MIC) and growth study of isolated bacteria carried out in Luria-Bertani media containing three different metals ions, zinc (II), copper (II), and iron (II), showed that a particular isolate termed Enterobacter cloacae NZS was found to exhibit better growth and tolerance for copper (up to 90 mM), zinc (up to 200 mM), and iron (up to 170 mM). Growth of the strain was notably well in the presence of iron (II). Compared to all the isolates, only E. cloacae NZS was able to be enumerated at pH lower than 5 while other strains were culturable only at pH 7. Its capability in iron (II) oxidation was preliminary assessed based on the pH, cell count, glucose consumption, and amount of iron oxidized throughout incubation in 9K media. E. cloacae NZS strain was found to be capable of oxidizing iron (II) supplied in 9K media to iron (III).

Conclusion

As preliminary investigation showed that E. cloacae NZS was able to oxidize iron (II) in 9K media at pH2, further optimization on the strain, medium, and culture conditions in future may be able to provide a better insight on this strain to be possibly used as an iron oxidizer for various applications.

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Effect of Indigenous Microbial Consortium on Bioleaching of Arsenic from Contaminated Soil by Shewanella putrefaciens

The effects of indigenous microbial consortium on removal of As from As-contaminated soil using an Fe(III)-reducing bacterium Shewanella putrefaciens were investigated under circumneutral pH condition. Sequential extraction of As revealed that more than 30% of As was associated with Fe(III)-(oxy)hydroxides in the soil. Bioleaching experiments were conducted anaerobically with a supply of lactate as a carbon source. The highest As removal efficiency (57.5%) was obtained when S. putrefaciens and indigenous bacterial consortium coexisted in the soil. S. putrefaciens and indigenous bacteria solely removed 30.1% and 16.4% of As from the soil, respectively. The combination of S. putrefaciens and indigenous bacteria led to a higher amount of labile As after microbial dissolution of Fe(III)-(oxy)hydroxides. After microbial treatment, soil quality represented by pH and organic content appeared to be preserved. The results indicated that the ecological and physiological understanding of the indigenous microbiome might be important for the efficient application of bioleaching technology to remove As from contaminated soils.