Comparison of extraction methods for quantifying extracellular polymers inbiofilms

Five commonly used extraction methods - regular centrifugation, EDTA extrac tion, ultracentrifugation, steaming extraction and regular centrifugation w ith formaldehyde (RCF) - were selected to study their effectiveness and rep eatability in extracting extracellular polymeric substances (EPS) from aero bic/sulfate reducing and nitrifying/denitrifying biofilm samples. Biofilm E PS extraction yields were represented by carbohydrate and protein concentra tions; the amount of cell lysis during the extractions was indicated by DNA concentration. The results showed that analyzing wash waters is essential in quantifying biofilm EPS; the contribution of this step varied from 8-50% of the total carbohydrate yield, depending on the extraction method. Among the extraction methods, the RCF extraction gave the greatest carbohydrate yield, the steaming extraction gave the greatest protein yield, and the oth er three extraction methods gave approximately equivalent amounts of carboh ydrate and proteins for both types of biofilm. DNA in the EPS was 27 times smaller than in the pellets, indicating no significant cell lysis occurred during the extractions. (C) 1999 IAWQ Published by Elsevier Science Ltd. Al l rights reserved.