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Differential Decay of Cattle-associated Fecal Indicator Bacteria and Microbial Source Tracking Markers in Fresh and Marine Water
Korajkic, A., B. McMinn, V. Harwood, N. Ashbolt, Mano Sivaganesan, AND O. Shanks. Differential Decay of Cattle-associated Fecal Indicator Bacteria and Microbial Source Tracking Markers in Fresh and Marine Water. ASM Microbe 2017, New Orleans, LA, June 01 - 05, 2017.
This study describes decay of various bacterial indicators originating from cattle manure.
Background: Fecal indicator bacteria (FIB) have a long history of use in the assessment of the microbial quality of recreational waters. However, quantification of FIB provides no information about the pollution source(s) and relatively little is known about their fate in the ambient waters. Microbial source tracking (MST) field has evolved in response to a need to identify pollution source(s), but majority of MST markers suffer from the same caveat as FIB, as our understanding of the factors influencing their fate in the environment is limited. Materials: We assessed the effect of water type (freshwater vs marine) and select environmental parameters (indigenous microbiota, ambient sunlight) on decay of FIB and MST markers from cattle manure. Experiments were conducted in situ using a submersible aquatic mesocosm containing dialysis bags filled with mixture of cattle manure and ambient water. Culturable FIB were enumerated by membrane filtration and via qPCR (Entero1a, EC23S) and MST markers were enumerated via qPCR and included general marker of fecal pollution (GenBac3) and cattle-associated subset (Rum2Bac, CowM2, CowM3). Results: Decay of culturable FIB was significantly faster (P > 0.001) than any of the molecular markers irrespective of the water type or experimental conditions. The water type was a significant factor affecting decay (P: 0.008 to < 0.001), although the magnitude of the effect differed among the microbial targets and over time. Presence of indigenous microbiota and exposure to sunlight were both significant factors (P:0.027 to < 0.001) for the decay of culturable FIB and CowM2, while Rum2Bac (P = 0.008) and CowM3 (P<0.001) were significantly impacted by either sunlight or indigenous microbiota. Conclusions: Our findings indicate that the intrinsic effects derived from secondary habitats (e.g. fresh and marine water) are important determinants of FIB and MST marker persistence. Selective exclusion of natural microbiota and/or sunlight typically resulted in extended survival, but the effect was limited to select microbial targets.