An electron micrograph of bacteria, evidencing nanowire connections amongst the archaea and Desulfococcus while in consortium. (Source: Gunter Wegener and the Max Planck Institute)
Symbiosis—the mutually beneficial relationship between two or more organisms—defines many evolutionary success stories, like that of the clown fish and sea anemone, as well as the coral-algae relationship. Most often, these relationships consist of a natural prey organism receiving the benefits of protection and nutrients while assisting its host or partner in capacities such as grooming, anchoring, or mobility. Researchers recently confirmed the existence of another symbiotic relationship, a relationship facilitated by nanoscale microbial power grids.
Near the bottom of the ocean, devoid of light, organisms such as bacteria exhibit energy production processes adapted to Earth’s primordial oxygen-less, sulfate and methane concentrated atmosphere (1). In particular, archaea have developed the ability to anaerobically oxidize methane as a means of producing energy (1). Meanwhile, primordial bacteria produce hydrogen disulfide from sulfate compounds through anaerobic respiration, reminiscent of how organisms operated in ancient atmospheric conditions (1, 2). These processes, while effective in fueling the bare vital functions of microbial extremophiles—organisms living in extreme conditions like volcanic lakes, high concentration sulfur environments, etc.—are still vastly inefficient in comparison with aerobic respiration and photosynthesis (1). As a consequence, bacteria and archaea often couple these reactions to optimize their respective energy production.
In a recently published paper, a research team from the Max Planck Institute, Wegener et al., confirmed that such a relationship existed between thermophilic archaea and sulfur-producing bacteria, Desulfococcus (2, 3). To test for the symbiotic relationship, researchers observed variations in the production rates of methane oxidation carbonate products and hydrogen disulfide in response to 1) changes in methane and sulfate concentrations (reactants for the respective energy production reactions) and 2) tampering with genes responsible for the production of cytochromes—molecules that accept and transport energetic electrons from energy production processes (3). Upon comparing native condition production levels, researchers observed astonishingly small changes in production levels and efficiency in response to environmental and cellular changes typical of generic microbial symbiosis resulting from the transfer of molecular intermediates. This finding led researchers to suspect that the crux of this symbiotic relationship’s efficiency resided in nanoscale power grids facilitating the transfer of electrons between the two energy production cycles (3).
Upon further analysis of the genomes of both microbial species, researchers discovered genes responsible for the construction of pili—microtubule structures that facilitate cell motion and anchoring—linked to key energy production DNA sequences (3). Wegener et al. realized that the networks of connected pili provided more efficient pathways for the transfer of energetic oxidation mediums such as cytochrome c, enhancing the methane oxidation and hydrogen disulfide production reactions (3). Furthermore, Wegener et al. discovered that these networks did not form unless the thermophilic archaea were in solution with Desulfococcus bacteria, emphasizing the symbiotic nature of the nano power grids (3). The presence of nanogrids connecting the methane oxidizing archaea and the Desulfococcus bacteria has been corroborated by a study published by McGlynn et al. The group used fluorescent protein tagging, nitrogen-15 isomer tagging, and transmission electron microscopy to confirm the presence of microtubules and energy intermediate transfer via pili between the two microbe types while in consortia—a mixed population of bacteria and archaea (4).
These studies provided valuable insight into the potential molecular pathways of energy transfer in microbes and a potential precedent for human endeavors at nanoscale energy transfer via organic materials. The researchers also made advances toward confirming the omnipresence of nanowire structures among archaea-bacteria consortia as a facilitator of energy transfer. Such advances hold promise for explaining primordial microbial colonies and for improving nanotechnology.
References:
- Obligate anaerobe. (2015, September 20). In Wikipedia, The Free Encyclopedia. Retrieved 21:08, October 27, 2015, fromhttps://en.wikipedia.org/w/index.php?title=Obligate_anaerobe&oldid=681970816
- Max-Planck-Gesellschaft. (2015, October 21). Nano power grids between bacteria: Microorganisms in the sea organize their power supply via tiny power-cables, thus oxidising the greenhouse gas methane. ScienceDaily. Retrieved October 25, 2015 from www.sciencedaily.com/releases/2015/10/151021135630.htm
- McGlynn, S., & Chadwick, G. (2105). Single cell activity reveals direct electron transfer in methanotrophic consortia. Nature, 526(7574), 531-535. doi:10.1038/nature15512
- Gunter Wegener, Viola Krukenberg, Dietmar Riedel, Halina E. Tegetmeyer, Antje Boetius. Intercellular wiring enables electron transfer between methanotrophic archaea and bacteria. Nature, 2015; 526 (7574): 587 DOI: 10.1038/nature15733