Energy in the form of electricity can be harvested from marine sediments by plac
ID: 145310 • 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.
Fig. 1. Electricity production by D. ace- toxidans in a two-chambered fuel cell, using only a solid graphite electrode as the electron acceptor. Cells (180 mg of protein per liter) were placed directly into the anaerobic anodic chamber and pro- vided with 1 mM sodium acetate. AQDS was added as an electron shuttling com- pound where indicated. The aerobic chamber was sterile, and the two elec- trodes were connected by a 500-ohm resistor.
3. Explain what fig. 1 shows, and how do the results support or refute the paper’s main points.
0.5 65 °C 29 Cells Acetate AQDS 0.4L O 0.3 0.1 0 0 50 100 150 200 250 300 Time (h)Explanation / Answer
Pairs of platinum mesh or graphite fiber-based electrodes, one embedded in marine sediment (anode), the other in proximal seawater (cathode), have been used to harvest low-level power from natural, microbe established, voltage gradients at marine sediment-seawater interfaces in laboratory aquaria. The sustained power harvested thus far has been on the order of 0.01 W/m2 of electrode geometric area but is dependent on electrode design, sediment composition, and temperature. It is proposed that the sediment/anode-seawater/cathode configuration constitutes a microbial fuel cell in which power results from the net oxidation of sediment organic matter by dissolved seawater oxygen. Considering typical sediment organic carbon contents, typical fluxes of additional reduced carbon by sedimentation to sea floors < 1,000 m deep, and the proven viability of dissolved seawater oxygen as an oxidant for power generation by seawater batteries, it is calculated that optimized power supplies based on the phenomenon demonstrated here could power oceanographic instruments deployed for routine long-term monitoring operations in the coastal ocean.
it can also be understood by another publication
Submillimeter depth distributions of total dissolved inorganic carbon (DIC) were derived from pH and profiles measured with microelectrodes in an organic-rich, laboratory-maintained sediment. The DTC profiles were used to calculate diffusive fluxes of DIC across the sediment-water interface. In two experiments, the calculated diffusive fluxes fell within ±50% of the total flux of DIC determined by core incubation. An assessment of errors suggests that the microelectrode-derived estimates are not significantly different from measured total DIC fluxes (P = 0.05). It is concluded, therefore, that pH and microelectrode measurements can be paired to determine finescale pore-water DIC profiles and DIC diffusive fluxes. Problems will arise only in situations in which pH and gradients are extremely steep or spatially heterogeneous; this is because these conditions can cause mismatching of pH and measurements or CO2 system disequilibrium.
ex:-
Besides all said advantages, batch cultures of E. coli in the presence of excess glucose or glycerol produce acidic fermentation by-products, in particular acetate Acetate is a known inhibitor of biomass and recombinant protein production , and the extent of its production is related to bacterial growth rate and to the availability of the carbon source , and is directly involved in the regulation of the central carbon metabolism . At pH 7.0–7.5, acetate is present in equilibrium with undissociated acetic acid. The latter, unlike charged acetate ions, can migrate uncontrolledly through bacterial membranes, disrupting the transmembrane pH and impairing cells viability . For this reason, several techniques have been devised to limit acetate accumulation. These include modifications of the growth medium composition through the addition of amino acids or minerals, the design of different process strategies (i.e. fed batch or dialysis culture) or gene engineering on the microorganisms to reduce acetate production and consequent accumulation ]. These methods are widely reviewed elsewhere [7, 19]. Cultures of E. coli K12 tend to produce more acetate compared to BL21 . This is one of the reasons why, although historically adopted in industrial processes, strain K12 is being gradually replaced by BL21 as the preferred microbial host for recombinant protein production. Moreover, recent multi-omics analysis have demonstrated that, compared to strain K12, BL21 possesses superior balance between amino acids production and degradation machineries, thus resulting in more efficient protein yields . Lower acetate production by BL21 compared to K12 is believed to be, in part, also a consequence of a more active glyoxylate shunt, which allows recycling part of the acetate produced during the fermentation toward other gluconeogenic cycles . A recent paper demonstrated that the phenotypic differences between the two strains is due to the high expression of acetyl-CoA synthetase (acs) in glucose exponential phase in BL21, which allows the simultaneous consumption of acetate and glucose .
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