Biphasic Decay Kinetics of Fecal Bacteria in Surface Water Not a Density Effect

Abstract

The decay of fecal bacteria in surface water often follows a biphasic pattern with the apparent first-order rate constant relatively high during a first phase and lower in a second one. This could be the result of population heterogeneity in resistance due to various mechanisms (different strains, genetically or nongenetically differentiated cells, different growth or cell cycle stage, clumping, hardening), or the specific decay rate could be directly or indirectly affected by the cell density (e.g., quorum sensing). All these mechanisms can theoretically produce a biphasic decay pattern and are consistent with the literature. However, they are fundamentally different and lead to different behavior of mechanistic total maximum daily load models, so identifying the correct mechanism is important. This technical note presents the results of a study aimed at determining if a density effect is involved. Laboratory decay experiments with pure strain