UMB (Ultramicrobacteria) have largely evaded cultivation from the environment since their earliest detection nearly four decades ago. However, the presence of UMB is largely undocumented, likely a correlation to their small cell, documented to occupy ranges between 0.2 microns and 0.009 microns. Since being previously identified as a majority in soil, UMB are now estimated to make-up nearly 15% of the entire bacterial domain thank to modern advances in modern DNA sequencing technology. It has been revealed that UMB are present in an increasing number of environments. It is proposed that their small size makes them physiologically adept at surviving in stressed environments. Traditionally thought to be inactive in the environment, it wasn't until active cultures were recently isolated from the Uranium contaminated waste site at the Y-12 National Security Complex at the ORNL (Oak Ridge National Laboratory), and the Rifle Colorado Uranium mining site that these organisms have been given proper attention for their role in Bioremediation.
Our knowledge of UMB is extremely limited leaving even the most basic questions regarding their growth, metabolism, diversity, phylogeny, and ecological role unanswered. Academic, and Government-sponsored groups from around the U.S. are working to understand these diverse and unique organisms. They include the Lawrence Berkley Lab, the lab of Jill Banfield, the Terry Hazen lab, Department of Energy’s ENIGMA project, the Oak Ridge National Laboratory, Pennstate University, and others. Studies are currently focused on National Priority EPA Superfund Sites at the former atomic testing laboratories at the Y-12 complex in Oakridge Tennessee, and the Riffle Colorado Uranium Mining site. Both sites are subject to chronic uranium groundwater contamination. Uranium is a radioactive element with a slow rate of decay, and is known for a wide variety of detrimental health impacts including chronic carcinogenic effects, and acute toxicity. Y-12 is also contaminated with nitrate, a potential toxin, and the most prevalent groundwater pollutant worldwide. Globally, communities and cities are plagued with undrinkable and unusable aquifers, making this a critical societal issue. It is proposed that these organisms are integral pioneers to disturbed community recovery. This knowledge could aid in the solution of some of the most challenging human health and quality of life impacts.
With our information of UMB growing to now encompass not only those organisms that use UMB size as a dormancy state for low nutrients or environmental stress. We have now discovered a variety of organisms which are considered active even at this small size. The high surface area to volume ratio of the small cell size leads to greater nutrient uptake, and could be a benefit to organisms living in such nutrient deplete environments. Recent genetic analyses have yielded results that support a very high expression of pili and pili-like features, which have been reported as being used to connect small and large cells together. There are still many questions regarding the relationship of these UMB to the surrounding microbial taxa. Furthermore, there are questions about whether these organisms can survive independently and if their small size makes them more responsive to remediation of pollution. These organisms leave a plethora of questions unanswered. The most important of which are related to growth, environmental response, and community structure. Current findings may be rather inconclusive about the roles of these organisms among the microbial community, but future projects are being used to unravel the mysteries which still surround these novel bacterial organisms and their role in bioremediation.
 Brown, C. T. et al. unusual Biology across a group comprising more than 15% of domain bacteria. Nature. 523, (2015).
 Luef, B. et al. Diverse uncultivated ultra-small bacterial cells in groundwater. Ncomms. 6, (2014).
 Hazen, T. C. et al., Environmental Systems Microbiology of Contaminated Environments. Bioremediation. Ch. 5.1, p.4. (2017).
 Smith, M. B. et al. Natural bacterial communities serve as quantitative geochemical biosenors. mBio 6, (2015).
 EPA. Superfund. www.epa.gov/superfund