Growth kinetics and chlorine resistance of heterotrophic bacteria isolated from young biofilms formed on a model drinking water distribution system

초록

The present work quantified the growth of young biofilm in a model distribution system that was fed with chlorinated drinking water at a hydraulic retention time of 2 h. Bacterial biofilms grew on the surface of polyvinyl chloride (PVC) slides at a specific growth rate of 0.14 ± 0.09 day-1 for total bacteria and 0.16 ± 0.08 day-1 for heterotrophic bacteria, reaching 3.1 × 104 cells/cm2 and 6.6 × 103 CFU/cm2 after 10 days, respectively. The specific growth rates of biofilm-forming bacteria were found to be much higher than those of bulk-phase bacteria, suggesting that biofilm bacteria account for a major part of the bacterial production in this model system. Biofilm isolates exhibited characteristic kinetic properties, as determined by μmax and KS values using the Monod model, in a defined growth medium containing various amounts of acetate. The lowest μ<inf>max</inf> value was observed in bacterial species belonging to the genus Methylobacterium, and their slow growth seemed to confer high resistance to chlorine treatment (0.5 mg/L for 10 min). K<inf>S</inf> values (inversely related to substrate affinity) of Sphingomonas were two orders of magnitude lower for acetate carbon than those of other isolates. The Sphingomonas isolates may have obligate-oligotrophic characteristics, since the lower KS values allow them to thrive under nutrient-deficient conditions. These results provide a better understanding and control of multi-species bacterial biofilms that develop within days in a drinking water distribution system. © 2015, The Microbiological Society of Korea.

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