An epifluorescence-based evaluation of the effects of short-term particle association on the chlorination of surface water bacteria

• The bacteria of largest hydrophobicity and smallest charge adhered best.
• Environmental isolates of adhered bacteria demonstrated chlorination resistance.
• Environmental particles demonstrated greater protection than goethite.
• Particle-mediated resistance showed a moderate relationship to bacterial adhesion.
• Bacterial adhesion played a larger role than the availability of protective sites.

Investigations into particle-mediated chlorination resistance were undertaken for three different bacteria (Escherichia coli ATCC 25922 and environmental isolates of Pseudomonas fluorescens and Serratia marcescens) and three different surfaces (goethite, environmental particles and surface-modified environmental particles). P. fluorescens demonstrated greater hydrophobicity than both other strains and proved the most adherent bacterium over all substrata investigated. Particle-mediated resistance to chlorination was investigated using short bacteria-particle association times and activity assays that employed sensitive epifluorescent detection. Consistent with adhesive behaviours, the bacterial strain that demonstrated the greatest particle-mediated chlorination resistance was the environmental strain of P. fluorescens. Resistance was observed to vary with both bacteria and particle type, and demonstrated a moderate correlation with adhesion (r2 ≥ 0.65). The short-term approach employed in our study demonstrates particle-mediated protection without the commonly assumed requirements of extracellular polymeric substances (EPS) or a large particle-based chlorine demand. Consequently, we have linked resistance with adhesion capacities and demonstrated a limit to resistance in the presence of additional particle protective sites (through increased turbidity) which appears to be driven by intra-population variance in bacterial surface characteristics. Finally, we observed important differences between behaviours of environmental versus laboratory-derived bacterial strains and particles, which highlight the importance of employing both approaches in characterising “real world” systems.

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