Monospecies Citrobacter sp. biofilms were grown in a laminar flow cell usin
g a carbon-limiting medium. Microelectrode measurements showed no change in
pH between the bulk fluid and biofilm when the flow cell was supplied with
the carbon-limiting medium under static or flowing conditions. When the bi
ofilm was supplied with a phosphate-limiting medium the biofilm became more
acidic than the bulk fluid and developed a gradient within. The implicatio
ns for metals-bioremediation processes are discussed.