Energy in the form of electricity can be harvested from marine sediments by plac
ID: 145430 • Letter: E
Question
Energy in the form of electricity can be harvested from marine sediments by placing a graphite electrode (the anode) in the anoxic zone and connecting it to a graphite cathode in the overlying aerobic water. We report a specific enrichment of microorganisms of the family Geobacteraceae on energy- harvesting anodes, and we show that these microorganisms can conserve energy to support their growth by oxidizing organic compounds with an electrode serving as the sole electron acceptor. This finding not only pro- vides a method for extracting energy from organic matter, but also suggests a strategy for promoting the bioremediation of organic contaminants in subsurface environments.
Analysis of 16S ribosomal DNA (rDNA) genes (3– 6) demonstrated that there was a pronounced enrichment of microorganisms from the subgroup of the Proteobacteria colonizing energy-harvesting anodes (7). Whereas only 17 4.3% (mean SD, n 3) of 16S rDNA sequences from control electrodes were in the subgroup of the Proteobacteria, 71.3 9.6% (mean SD, n 3) of the 16S rDNA sequences from microorganisms colonizing anodes of the current-producing batteries were in this sub- group. Furthermore, 70% of the increase in Proteobacterial sequences was due to a single cluster of bacteria in the family Geobacteraceae, a group of anaerobic microorganisms that can couple the oxidation of organic com- pounds to reduction of insoluble Fe(III) oxides (8, 9). The organism in pure culture most closely related to the sequences repeatedly enriched on anodes (7) was Desulfuromonas acetoxidans, a marine microorganism known to grow anaerobically by oxidizing acetate with concomitant reduction of elemental sulfur (10) or Fe(III) (11). Enumeration of Desulfuromonas 16S rDNA sequences by a most- probable-number polymerase chain reaction (MPN-PCR) technique (12) revealed that Desulfuromonas target sequences on anodes from current-generating batteries were enriched by a factor of 100 relative to those on anodes from control batteries.
To further investigate the specific enrichment of microorganisms on anodes, we inoculated the anoxic side of a two-chambered microbial battery with sediment; the seawater was periodically changed with fresh acetate-amended anoxic seawater (13). Replacing the medium diluted the sediment and microorganisms from the inoculum that were not growing, while re- supplying acetate, the primary intermediate in the degradation of organic carbon in anoxic sediments (14). After 85 days, 16S rDNA sequences from bacteria attached to the anode were examined. All of the anode-attached bacteria detected were members of the Proteobacteria, with the majority (70%) of the sequences most closely related to the genus Desulfuromonas.
Explain what supplementary figure1 shows, and how do the results support or refute the paper’s main points.
Explanation / Answer
The enrichment of bacteria on electricity harvesting anodes is clearly seen above graph, where the percentage of 16 S rDNA clones are higher in which electricity is harvested.
Proteobacteria species are able to produce electricity when compared to the Cytophoga flavobacterium species.
The subgroup 3 in protebacteria species shows a significant electricity production when compared to the other sub groups.
Bioremediation can be done through using proteobacteria sub group 3 species and Gram + ve species. They can convert organic waste into useful electricity.
It clearly suggests that the majority current producing species are belongs to family Geobacteraceae.
The proteobacteria sub group which produces current belongs to the genus Desulfuromonas.
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