ISOTOPE-DILUTION ANALYSIS AND RATES OF P-32 INCORPORATION INTO PHOSPHOLIPID AS A MEASURE OF MICROBIAL-GROWTH RATES IN BIOFILMS

The method described represents an alternative to the H-3 thymidine in corporation technique in the determination of bacterial growth rates w ithin biofilms. The effect of increasing incubation duration was inves tigated, and incorporation rates found to approximate towards linearit y for ca Ih. Isotope dilution analyses were carried out in an attempt to measure dilution of added P-32 by phosphate that was being cycled i nternally within the biofilm. Statistically significant differences (P < 0.001) were found in rates of phospholipid synthesis in biofilms fr om the River Conwy during different seasons. A close correlation was f ound in a comparison of H-3 thymidine incorporation and P-32 incorpora tion techniques (r = 0.82; P < 0.001) in data collected from the river s Conwy, Clywedog and Aber in North Wales. That close correlation sugg ested that the isotope dilution analysis technique was successful in o vercoming potential problems caused by the pool of internally cycled p hosphate. The alterantive H-3 thymidine incorporation approach cannot be used with sulphate reducing bacteria. And so finally, it was propos ed that the P-32 incorporation technique could prove of value in measu rements of the growth of sulphate reducing bacteria in biofilms causin g metal corrosion.