Extremophile bacteria could be key to solving nuclear problems

May 26, 2015 by Sam Wood

Radiation-tolerant bacteria could be even more effective at clearing up nuclear waste through natural processes than previously thought.

Last year, a team from the University of Manchester discovered an 'extremophile' microorganism in the Peak District, capable of breaking down organic material that is present in nuclear waste, preventing the organic compounds from leaching out key radioactive elements into the environment.

Other studies from the group have shown that land contaminated with radioactive waste can also be cleaned up by bacteria that convert soluble forms of radionuclides, such as uranium, to insoluble forms that are less hazardous and mobile. However, for this to be useful, a critical question has needed addressing for some time; whether these unusual naturally occurring activities are killed off by radiation associated with the radioactive waste.

Now in a new paper published today in the journal Applied and Environmental Microbiology the team explain how they have discovered that radiation could actually allow certain microbes to thrive, rather than killing them, possibly including a species known to transform radioactive material into much more stable forms. Hence, radiation could make them more effective in the cleanup of contaminated land or in contributing to the safety of radioactive waste disposal in the long-term.

Professor Jonathan Lloyd, who has led the research at the University of Manchester, said, "This could provide a new, and very useful extra layer of protection when we are trying to dispose of nuclear waste. There are advanced plans on how this can be done safely, often involving the use of concrete and steel barriers, but there is recognition that at some point in the distant future these barriers will be breached.

"But by assessing the ability of these useful microbes to survive radiation stress, we can be more confident that the waste will remain locked-up for very long periods of time (many thousands of years), helped by a naturally evolving "biobarrier". Before this research, the assumption was that the radiation would probably kill off the bacteria that we are studying, but it seems that is not the case. It is potentially a very important finding for the nuclear industry, and illustrates how resilient biology can be!"

Getting rid of nuclear waste poses a big problem for the UK, with very large volumes destined for burial deep underground. The largest volume of radioactive waste, termed 'intermediate level' and comprising of 364,000m3 (enough to fill four Albert Halls), will be encased in concrete prior to disposal into underground vaults. When ground waters eventually reach these waste materials, they will react with the cement and become highly alkaline.

Explore further: Scientists discover hazardous waste-eating bacteria

More information: "The impact of gamma radiation on sediment microbial processes." Appl. Environ. Microbiol. AEM.00590-15; Accepted manuscript posted online 3 April 2015, DOI: 10.1128/AEM.00590-15

Sept 9 2014 Scientists discover hazardous waste-eating bacteria

Tiny single-cell organisms discovered living underground could help with the problem of nuclear waste disposal, say researchers involved in a study at The University of Manchester.

Although bacteria with waste-eating properties have been discovered in relatively pristine soils before, this is the first time that microbes that can survive in the very harsh conditions expected in radioactive waste disposal sites have been found. The findings are published in the ISME (Multidisciplinary Journal of Microbial Ecology) journal.

The disposal of our nuclear waste is very challenging, with very large volumes destined for burial deep underground. The largest volume of radioactive waste, termed 'intermediate level' and comprising of 364,000m³ (enough to fill four Albert Halls), will be encased in concrete prior to disposal into underground vaults. When ground waters eventually reach these waste materials, they will react with the cement and become highly alkaline. This change drives a series of chemical reactions, triggering the breakdown of the various 'cellulose' based materials that are present in these complex wastes.

One such product linked to these activities, isosaccharinic acid (ISA), causes much concern as it can react with a wide range of radionuclides - unstable and toxic elements that are formed during the production of nuclear power and make up the radioactive component of nuclear waste. If the ISA binds to radionuclides, such as uranium, then the radionuclides will become far more soluble and more likely to flow out of the underground vaults to surface environments, where they could enter drinking water or the food chain. However, the researchers’ new findings indicate that microorganisms may prevent this becoming a problem.

Working on soil samples from a highly alkaline industrial site in the Peak District, which is not radioactive but does suffer from severe contamination with highly alkaline lime kiln wastes, they discovered specialist “extremophile” bacteria that thrive under the alkaline conditions expected in cement-based radioactive waste. The organisms are not only superbly adapted to live in the highly alkaline lime wastes, but they can use the ISA as a source of food and energy under conditions that mimic those expected in and around intermediate level radwaste disposal sites. For example, when there is no oxygen (a likely scenario in underground disposal vaults) to help these bacteria “breathe” and break down the ISA, these simple single-cell microorganisms are able to switch their metabolism to breath using other chemicals in the water, such as nitrate or iron.

The fascinating biological processes that they use to support life under such extreme conditions are being studied by the Manchester group, as well as the stabilizing effects of these humble bacteria on radioactive waste. The ultimate aim of this work is to improve our understanding of the safe disposal of radioactive waste underground by studying the unusual diet of these hazardous waste eating microbes.

One of the researchers, Professor Jonathan Lloyd, from the University's School of Earth, Atmospheric and Environmental Sciences, said: “We are very interested in these Peak District microorganisms. Given that they must have evolved to thrive at the highly alkaline lime-kiln site in only a few decades, it is highly likely that similar bacteria will behave in the same way and adapt to living off ISA in and around buried cement-based nuclear waste quite quickly.

"Nuclear waste will remain buried deep underground for many thousands of years so there is plenty of time for the bacteria to become adapted. Our next step will be to see what impact they have on radioactive materials. We expect them to help keep radioactive materials fixed underground through their unusual dietary habits, and their ability to naturally degrade ISA."

The paper "Microbial degradation of isosaccharinic acid at high pH” is published in The ISME Journal, DOI: ISMEJ.2014.125