A key factor governing growth of all organisms is nutrient
availability. All human pathogens are heterotrophs, utilizing
organic compounds as their carbon and energy source. Natural
organic matter in water comprises a broad spectrum of many
different compounds; it is usually determined as a bulk parameter,
such as dissolved organic carbon (DOC). Only a fraction
(0.1 to 44%) of this DOC pool is readily available for bacterial
growth (18, 33). This bioavailable fraction is quantified using
bioassays, such as the biodegradable dissolved organic carbon
(BDOC) assay (27) or the assimilable organic carbon (AOC)
assay (31). Typically, AOC represents small molecules readily
available for growth, whereas BDOC can also include larger
molecular compounds, which require predegradation before
they can be taken up by microbial cells. Results from both of
these assays are commonly used as indicators for bacterial
growth potential and have previously been associated with