October 29th, 2012 by Michael Ricciardi
The ‘electric bug’, or more specifically, a form of bacteria, was first discovered in 2010 by Danish scientists studying the mysterious chemical fluctuations in the sediment of Aarhus Bay. They had observed a strange chemical linkage between oxygen levels in the water and reactions in the deeper sediments that was faster than chemical theory could explain.
The only thing that could explain such a rapid reaction was the presence of a significant electric field or signal. But what could be causing it? It was thought improbable that such a large effect over so large an area could be achieved by bacteria; no known microbial species fit the bill.
But recently, the bacterial theory was confirmed with the identification of the bug as a member of the microbe family Desulfobulbaceae. This particularly electrifying member shares 92% of its genetic material with the other members of this family, which might seem like a great deal of similarity. But differences in species, even whole genuses, are the result of much smaller percentage differences.
Thus, some researchers suggest that the microbes — which belong to a larger clade of proteo-bacteria — should be considered a whole new genus. The study of this new genus may create a new scientific discipline that integrates biology, geology, and chemistry — one seeking to reveal the electro-chemical links between microbial life forms and the sea floor sediment.
Living Power Cables
The bacteria have a unique cellular structure — looking like identical cogs in some vast machine — that seems perfectly suited to electrical conductance. The bugs fit together in long filaments, capable of forming vast stretches of desulfobulbaceae “cable.” (the microbes are sometimes referred to as “cable bacteria”). So vast, in fact, that a mere teaspoon of sea-floor sediment (from the bottom of Tokyo Bay) was found to contain a half mile of this organic cable. Due to this collective structuring ability, the researchers here assert that the bacteria should be considered a metacellular life form (or metazoan).
While the exact chemical mechanism of electricity generation is not known just yet, it is theorized that the transport of electrons (what’s necessary for any electrical current to flow) occurs between two layers of sediment: the top, oxygen-rich layer, and the slightly deeper (one inch or so) oxygen-depleted layer. This lower anoxic layer is richer in the element sulfur (S) in the form of SO4 and H2S ions. It is speculated that the microbes break down the H2S molecules and transport freed electrons (via the broken H+ bonds) to the upper oxic layer, attracting oxygen, and forming water as an end product. The result of this chemical activity is a continuous electric current.
Benefiting Life Under Sea and On Land
‘Living, electrical cables add a new dimension to the understanding of interactions in nature and may find use in technology development.‘ (the authors, abstract)
But the team has verified that the bacteria are in fact chemically breaking down iron sulfides (FeS2) and carbonates (FeCO3) in the lower layers and producing iron oxide (FeO2) and magnesium calcite precipitate in the upper layer. These are crucial mineral nutrients for life in the oceans — and even for land-dwelling lifeforms who require the same nutrients.
It is not yet known how much of the global sea floor contains these bacterial forms. It is possible that much of the ocean floor will be found to be pulsing with electrical power from these living power cables. These newly discovered microbes could turn out to be a fundamental component to what’s known as Earth’s “deep time” cycle — perhaps being (literally) the pulse of the biosphere.
The research team included microbiologists Christian Pfeffer, Nils Risgaard-Petersen, and Lars Peter Nielsen of Aarhus University (see complete list of team members in link below).
The bacteria are described in the Oct. 24 edition of the journal Nature, under the title “Filamentous bacteria transport electrons over centimetre distances.”
Some source material for this post came from the WIRED article “Electric Bugs: New Microbe Forms Living, Deep-Sea Power Cables” by Brandon Kelm
Top Image: (SEM of Escherichia coli, a type of proteobacteria) US NIAID
Diagram: Nils Risgaard-Petersen via WIRED
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