THE BIOFILM POLYSACCHARIDE MATRIX - A BUFFER AGAINST CHANGING ORGANIC SUBSTRATE SUPPLY

In contrast to the widely held view that microorganisms respond rapidly to changes in environmental conditions, the microbes in biofilms appear remarkably resilient to substantial changes in the abundance of dissolved organic substrates. Removal of high-molecular-weight dissolved materials from waters supplied to river biofilms generally did not affect bacterial densities or the synthesis of phospholipids and DNA. Even the complete elimination of exogenous materials from the overlying waters allowed heterotrophic activity to continue unaffected. Moreover, that continued activity was not supported by the catabolism of endogenous reserves of C (poly-beta-hydroxy alkanoate-PHA). The addition of inorganic nutrients to substrate-free waters allowed heterotrophic activity to increase within the biofilm. Since neither exogenous sources of river DOC or endogenous reserves (PHA) served as the source of C, we propose that an alternative, namely the polysaccharide matrix (and any absorbed or incorporated organic matter), served as the primary carbon reserve for biofilm microorganisms during the imposed organic substrate deprivation.