ABSTRACT
Gram-positive and gram-negative bacterial surfaces are good interfaces for the sorption of dilute environmental metal cations. Once metal ions have interacted with the electronegative sites on the surface macromolecules, they nucleate the formation of fine-grained minerals by incorporating common anions from their surroundings, encouraging further metal complexation. In the electron microscopy the cell wall of most gram-positive bacteria such as Bacillus subtilis appears as an amorphous layer approximately 20 to 25 nm thick. Bacteria may possess other surface structures such as pili or fimbriae, flagella, spinae, S-layers and capsules. Crystallinity usually correlates with increasing depth within the subsurface environment. Like all other groups of living organisms, bacteria come in a vast range of shapes and sizes. Biofilms are ubiquitous and formidable entities on surfaces in the natural environment and therefore must have a major impact on the chemistry and microbiology of the water immediately overlying them.
