Surfaces formed by extracellular polymeric substances enclosing individual
and some small communities of {\it Acidithiobacillus ferrooxidans} on plates of
hydrophobic silicon and hydrophilic mica are analyzed by means of atomic force
microscopy imaging. Accurate nanoscale descriptions of such coverage surfaces
are obtained. The good agreement with the predictions of a rather simple but
realistic theoretical model allows us to conclude that they correspond, indeed,
to minimal area surfaces enclosing a given volume associated with the encased
bacteria. This is, to the best of our knowledge, the first shape
characterization of the coverage formed by these biomolecules, with potential
applications to the study of biofilms.Comment: 4 pages, 9 figures. v2: minor changes. v3: Terminology changes and
extra references included. v4: Final versio