Iron aggregation in biofilms does indeed occur. Essentially many bacterial
surface polymers are anionic due mainly to carboxylate or phosphate residues.
These surface polymers include capsules, peptidoglycan, teichoic and
teichuronic acids, and to a smaller extent membrane phospholipids and
lipopolysaccharides (particularly those with acidic O antigens). These anionic
residues will attract and bind cations such as Fe. Depending upon the chemical
environment and metabolism of the organisms within the biofilm, the bound iron
may precipitate and form a number of different minerals.
Several reviews have been published on this subject including:
Beveridge, T.J. Annual Review of Microbiology 43: 147-171, 1989
Kasan, H.C. Critical Reviews in Environmental Science and Technology 23:79,
McLean, R.J.C. et al., Canadian Journal of Microbiology 42: 392-400, 1996
Ehrlich, H.L. and Brierley, C.L. 1990. Microbial Mineral Recovery,
McGraw-Hill, New York (chapters 9 - 14 written by several authors cover
various aspects of biosorption)
As for your question relating to biofilm growth at pH 11 in the presence of
EDTA: I am not aware of this having been reported. If you have encountered
this phenomenon, I would certainly investigate it.
Southwest Texas State University
San Marcos, Tx 78666
Email: RM12 at swt.edu