Reactorbacillus

              One of the more controversial bioforming techniques makes use of the ability for certain microbes to accumulate rare earth metals, and more worrying span the gap between biological life and nuclear power.

Table showing some uranium concentrations of common crustal rocks, and other sources

Taking only one element into consideration, uranium, we can see that although relatively little is present in a variety of materials, and very much dispersed, but as soon as we start to process rock on metres cubed scale we can quickly accumulate significant amounts of uranium. A tonne (or put another way, a million grams) will on average contain a few grams of uranium, and also some other radioisotopes, and engineered bacteria will quite happily extract this for free. (Also uranium oxidation is an exothermic process providing the bacteria with a potential energy source to drive their cellular processes)

            Bacteria have already been extensively used to dissolve away rock, to generate large subterranean cavities, usually for terraforming projects, the projects generate huge caverns which can stably hold water, or accommodate for storage of other things, which is useful when one wants to start engineering an existing environment. The outcome of this is that the solutions that the rock eating bacteria generate will contain significant amounts of rare earth metal, and the processes tend to generate millions of metres cubed of excavation, meaning literally tonnes of uranium.

            Reactorbacillus is a engineered microbe made from a combination of different existing bacteria which have some bioleaching abilities, as well as the inclusion of completely new genes which have artificially developed, some species of reactor bacillus work independently of mining microbes slowly dissolving the rock themselves, others are part of a greater community of engineered microbes, but all have one ability, to accumulate rare earth metals. Usually uranium and other rare earth metals are fused into ‘sulphur clusters’ that reside in the cell, the relatively small amounts of rare metals, even in the increased concentration in the cell do little to harm it. However of cell death, the precipitation of these bacteria from the medium form highly enriched deposits. It is in this increased concentration that the accumulated radio-nucleotides begin to function as a reactor, as enough material is in such close proximity.

            In this way biological agents can be used to generate natural reactors, nearly anywhere. As far as terraforming projects are concerned this is of remarkable benefit as these natural reactors can provide vast amounts of heat, with no real energy required in their generation. The process also prevents the accumulation of a critical mass of radioisotopes, as the heat and radiation given off by the functioning reactor act to sterilize the immediate environment, prevent further accumulation of fuel from the bacteria. Most systems equilibrate over time generating a low output reactor which is continuously fed by the lifecycle of the microbes. It could be thought that this process would generate an unenviable amount of radioactive waste, but these reactors are usually hundreds of metres below ground, and the reactor in a very small confined area, though there is some risk of losing radioisotope through water seepage, the complexes of metals formed are relatively insoluble and inert and so stay put.

Additional notes

Formation of a natural reactor using uranium is dependent on the concentration of 235U, when proportions of this isotope fall below 1% (in relation to 238U) then no amount of uranium accumulation will result in criticality. For this reason this method is restricted either to younger planets (higher relative abundance of 235U), or to particularly nuclide rich worlds.