It is well reported that a low pH (2-4) favours efficient leaching or mobilisation of heavy metals from water/soil/industrial wastes.
If we use alkali tolerant/alkaliphilic bacteria which grows well at pH 11-12 and produces organic acid and neutralizes the medium (brings down the high pH to 8), how efficient it is to solubilise or mobilize the heavy metals in the medium? What is the mechanism of bioremediation of the heavy metals by such bacteria? Does only the organic acid produced by bacteria work or are some other factors (such as redox reactions, siderophores etc.) also involved in it?
There are not many publications on bioleaching under alkaline conditions. Some of the alkalitolerant bacteria seem to have good leaching potential (see e.g., Sklodowska and Matlakowska (2007) in: Donati and Sand (eds.) Microbial Processing of Metal Sulfides, pp.121. More recently, biological treatment and metal mobilization from alkaline solids by mainly Bacillus has been addressed (see Chiang et al. (2013) Minerals Engineering 48:116)
If bugs are alkaliphilic but produce organic acids, medium will become less alkaline to a point they will stop growing.
Not all heavy metals are movable just in acidic conditions, e.g. U can form soluble complexes with carbonate in alkaline conditions so it is even used in mining, Mo as molibdate is much more available in alkaline conditions,...
Respect biomining in non-acidic conditions, it is not necessarily alkaline you can take a look to the following review, though it is a bit old.
Jain, N. & Sharma, D.K., 2004. Biohydrometallurgy for nonsulfidic minerals - A review. Geomicrobiology Journal, 21(3), pp.135–144. Available at: http://www.tandfonline.com/doi/abs/10.1080/01490450490275271
In general, organic acids may form complexes with heavy metals making them soluble. It is known that some of this acids like citric or oxalic have important interactions with some metals but all this will be dependent on the exact acid and conditions of pH, ionic strength...
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