Intensive farming combined with global warming significantly increases land erosion, resulting in major environmental effects. Danish researchers have discovered that electrically conductive particles usually washed away through erosion may have an unexpected effect. The particles enable an unusual partnership between bacteria that produce considerable greenhouse gas. The researchers hope to use these bacteria sustainably for storing electricity and carbon.
Bacteria, like humans, vary tremendously. Most bacteria prefer to live at normal temperatures and in normal environments. Some thrive, however, in extreme cold and heat, under extreme pressure, in extreme salinity or in extreme acidity. Some feed on organic material, and others prefer rocks or metals. Danish researchers have now discovered, buried in the coastal sediments of the Baltic Sea, a very unusual partnership in which Geobacter bacteria feed Methanosarcina microorganisms with electricity.
“During our research in the Gulf of Bothnia between Sweden and Finland, we discovered a very unusual partnership between two microorganisms that share a meal, so to speak. One feeds on organic material from the sediment but has nothing to respire and thus releases electrons onto minerals, which will be feeding another species that converts carbon dioxide methane,” explains Amelia-Elena Rotaru, University of Southern Denmark, a main author.
The two different microbes requice electrically conductive minerals for their collaboration. This is where land erosion comes into play. Erosion could transport conductive particles into the sea.
"Thus it may create the ideal conditions for this odd couple of microorganisms, one of which makes electrical currents to feed the one that emits methane, a potent greenhouse gas."
Mysterious symbiosis in the Baltic Sea
The researchers selected the Gulf of Bothnia, into which eight rivers in Sweden and Finland flow. In particular, the runoff from nearby forestry and coastal industries and increased land erosion inputs conductive minerals into the Gulf, including the conductive particles that are essential for the collaboration between Geobacter and the methane-producing Methanosarcina.
“This is the first time researchers have discovered this type of electrical collaboration between these kinds of microorganisms in the environment. The study shows that, as long as conductive particles were available, both continued to grow, but if we removed the conductive particles, Geobacter died off and the methane-producing Methanosarcina dramatically decreased its activity.”
The symbiosis involves Geobacter feeding Methanosarcina with electrons via the conductive particles. Because of Methanosarcina’s ability to retrieve electrons from conductive particles it could outcompete other microorganisms that would usually thrive in this environment.
“The conductive particles are crucial for the survival of these bacteria. One example of conductive particle that washes out through land erosion in the Baltic Sea is an iron mineral – magnetite, and the increased input of this mineral into the Baltic might affect the composition of bacteria in the immediate environment and the emission of greenhouse gases in general.”
This new knowledge is important because it shows us the potential negative impact of land erosion in generating the greenhouse gas methane.
Positive impact of such partnerships
However, it is equally important to use such knowledge for converting waste into methane and then use it as natural gas.
“We cannot easily control the natural production of methane, but we can reduce the input of these conductive particles originating from excessive deforestation and agricultural amendments. On a more positive note, we could use electrically conductive particles to optimize the growth of microorganisms in the digester tanks in which waste is converted to natural gas.”
Instead of focusing on preventing the negative impact of microorganisms, Amelia-Elena Rotaru and her team are attempting to find a way of getting the microorganisms to work for us to store energy and carbon dioxide into multi-carbon chemicals substituting fossil fuel based chemicals required by various industries.
“If we can find a way to use the electrical properties of microbes to store carbon and electricity while producing biodegradable and safe materials similar to those made today from fossil fuels, we will achieve our ultimate goal of fostering a sustainable society,” concludes Amelia-Elena Rotaru.
”Conductive particles enable syntrophic acetate oxidation between Geobacter and Methanosarcina from coastal sediments” has been published in mBio. The Novo Nordisk Foundation awarded a grant in 2015 to a main author, Amelia-Elena Rotaru, for the project Microbial Chemical Plants: Harnessing Microbial Metabolism for the Production of Valuable Chemicals.