Darius Labie
Here are some interesting facts about the bacterium that I have chosen to adopt, Candidatus Desulforudis audaxviator - an ancient and lonely bacterium that may shed light on some of sciences big topics like the nature of early life on Earth, the requirements to sustain the simplest life forms and ecosystems, and the possibility of extra-terrestrial life forms.
D. audaxviator is a rod-shaped, Gram-positive, motile, spore-forming, thermophilic bacterium that was discovered in 2006 in a South African gold mine, 2.8 km deep (a depth that was, prior to the discovery of this bacterium, thought to be uninhabited by life) in a 60° C fluid-filled fracture in uranium-rich rock. This bacterium is the sole inhabitant of its environment (making up 99.99% of the biological life present in a fluid sample taken from the fracture- as determined by DNA sequencing) and has subsequently been found at this depth in other continents. It is an obligate anaerobe that obtains its energy through the dissimilatory reduction of sulphate in the presence of radiation and it is capable of carbon and nitrogen fixation. The discovery of this bacterium has the potential to shed light on questions regarding life that existed on Earth millions of years ago as well as the possibility of extra-terrestrial life.
The species name, audaxviator, means bold traveller and was inspired by the latin phrase “…descende, audax viator, et terrestre centrum attinges.” from Jules Verne’s “Journey to the centre of the Earth” which translates to “… descend, bold traveller, and you will attain the centre of the Earth.” Which is quite fitting because this bold traveller is closer to the centre of the Earth than any other known living organism.
Few organisms are similar to D. audaxviator in that it is anaerobic chemolithoautotroph ie. it is capable of using inorganic sources of energy instead of consuming organic molecules as food or needing sunlight, it can fix its own carbon from inorganic carbon present in its environment rather than relying on plants to convert carbon dioxide to organic compounds, and utilisez sulphate instead of oxygen as the final electron acceptor during cellular respiration. D. audaxviator can also fix its own nitrogen from ammonia and use it to synthesize all the amino acids necessary to support life, hence not needing to acquire any of them from its environment. D. audaxviator’s numerous metabolic pathways are a major contributing factor to its ability to exist independently of other life. Its 2.35 Mbp genome encodes, in 2157 protein-encoding genes, the entire biological component that is necessary to sustain a single-species ecosystem, completely independently of other life forms. It obtains energy anaerobically through dissimilatory sulphate reduction, this process is characterized by the production of inorganic sulphide, which is also present in small amounts in the rock surrounding the fracture in which it was found. D. audaxviator utilizes the inorganic sulphide present in its environment by reacting it with hydrogen peroxide which is produced by radiolysis of the water within the fracture. Radiolysis is achieved by the radioactive decay of uranium that is present in the rock. It basically eats radiation! D. audaxviator does not require organic carbon because it is capable of carbon fixation and thus obtains its carbon from gasses such as carbon dioxide, methane and formate in the rocks. The bacterium is also capable of nitrogen fixation, and it obtains nitrogen from ammonia. It is also capable of using this nitrogen to synthesize all the amino acids that are necessary for life. D. audaxviator is capable of forming endospores which allow it to persist through unfavourable conditions. It is also motile and therefore capable of moving towards nutrients in response to a chemical gradient. These unique characteristics of this bacterium makes D. audaxviator capable of complete independence from other organisms.
Follow the link to learn more about how this bacterium survived all alone for so long https://www.nature.com/news/2008/081009/full/news.2008.1160
According to the DNA sequencing results obtained by Chivian et al (2008), D. audaxviator possesses many genes that were acquired though horizontal gene transfer (a topic we will be discussing in MICR311) between an ancestor of D. audaxviator and ancient archaeal species. These genes encode the synthesis of an archaeal nitrogenase, a sulfate adenyltransferase, and the formation of gas vesicles). They have conferred benefits to the bacterium that have allowed it to survive in isolation for so long. Follow the link to learn more
D. audaxviator is an endolithic bacterium, meaning it lives within rocks-this also makes it an extremophile because rocks are an inhospitable environment. It is also thermophilic, meaning it is capable of withstanding high temperatures that would normally kill living things. D. audaxviator is a polyextremophile – an extremophile that is capable of withstanding two or more extreme conditions. Furthermore, it is intolerant of oxygen and simply requires sulphate, water, radiation, ammonia and carbon dioxide to exist- all of which are found together in various rocky bodies throughout the universe (for example, Mars, Pluto, and theoretically countless asteroids and meteoroids). The discovery of this bacterium suggests that if we do find extra-terrestrial life, it is unlikely to resemble the little green men we’ve all been expecting but rather it will possibly resemble an organism such as D. audaxviator. The scientist that discovered the bacterium hypothesized that if life existed that deep in the Earths crust it is likely to resemble extra-terrestrial life, and thus found this bacterium. Reading the following articles made me realize just how exciting, vast and sometimes even extreme our work really is as microbiologists.
follow the hyperlinks to articles about the scientists that discovered this bacterium and how it all transpired (https://pr.princeton.edu/pwb/99/1213/microbe.shtml)(https://serc.carleton.edu/microbelife/extreme/endoliths/index.html)
