[mtwalsh01]

The original post in this thread mentions one form of bioremediation called biostimulation “in which bacteria are motivated to start the process of bioremediation”. There are various examples in which the process of biostimulation can be used effectively to encourage the indigenous bacterial community to tackle environmental pollution. One recent study describes handling of the high concentrations of uranium (VI) generated from the mining of leachate in the Witwatersrand Basin, South Africa. In this study, tolerance of the indigenous bacterial species to high U(VI) concentrations along with the required amount of citric acid were optimised. Two bioreactor studies were performed. In the first, U(VI) was removed effectively from both low and high concentrations of U to below the levels set as safe for drinking water by South African National Standards. The second adapted to increasing U(VI) levels in feed water in the presence of sufficient electron donors. Relevant bacterial species such as Desulfovibrio and Geobacter were identified, which are known to reduce U(VI). Uranium was both precipitated intracellularly and as U(IV) oxides and TEM-EDS. The study confirmed the possibilities for optimising the tolerance of the indigenous bacteria for remediation of U(VI) and suggests that their system can be upscaled.

As previous posts have mentioned, it is important to be mindful of potential alterations in bacterial population diversity and abundance following bioremediation strategies including biostimulation. For example, one recent study examined consequences for bacterial abundance and diversity after biostimulation on anoxic marine sediments with high metal content. Molecular fingerprinting and next generation sequencing was used to characterise the bacterial population.  Adding organic (lactose and/or acetate) and/or inorganic compounds induced significant increases in bacterial growth but also changed bacterial diversity and assemblage composition. In experimental systems, supply of organic substrates only resulted in increases in the relative importance of sulphate reducing bacteria of the Desulfobacteraceae and Desulfobulbaceae families accompanied by a Flavobacteriaceae taxa. The opposite effect was achieved by when inorganic nutrients were also supplied. Increased bacterial metabolism along with the increase of bacterial taxa affiliated with Flavobacteriaceae resulted in a significant decrease of Cd and Zn associated with sedimentary organic matter and Pb and As associated with the residual fraction of the sediment. However, independent of the experimental conditions investigated, there was no dissolution of metals suggesting that bacterial assemblages were important in controlling metal solubilisation processes. The results of this study have thus clarified important biogeochemical interactions which influence metal behaviour and advance understanding of potential consequences of bio-treatments on fate of metals in contaminated marine sediments.

References
Maleke M, Williams P, Castillo J, Botes E, Ojo A, DeFlaun M, van Heerden E. Optimization of a bioremediation system of soluble uranium based on the biostimulation of an indigenous bacterial community. Environ Sci Pollut Res Int. 2014 Dec 30. [Epub ahead of print]

Fonti V, Beolchini F, Rocchetti L, Dell'Anno A. Bioremediation of contaminated marine sediments can enhance metal mobility due to changes of bacterial diversity. Water Res. 2014 doi: 10.1016/j.watres.2014.10.035. [Epub ahead of print]