Evolutionary patterns of Escherichia coli growth in seawater determined with a Host to Coast Environmental Laboratory Analog

Abstract

The present study investigated evolution- ary patterns of Escherichia coli growth and survival in transmission through the coastal ecosystem between human host and seawater using a novel 'Host to Coast' Laboratory Analog simulating an 11 d sequence cycling through the pH and temperature conditions of the small intestine, colon, sewer, seawater, human stomach, and back into the small intestine. Although historically E. coli has been assumed to die off rapidly in seawater, a few instances of E. coli growth have been observed in environmental fresh water, soils, and nutrient- enriched tropical seawater, suggesting the potential for evolving greater viability in such environments. This study investigated whether E. coli can evolve increased capacity for growth and survival in seawater through selective exposures to singular abiotic factors such as the high alkalinity or low temperatures approx- imating coastal aquatic conditions, and also whether adaptation to cycling pH can lead to increased growth fitness in a human host. Specialists and generalists were examined to reveal patterns of trade-offs in the multi-stress environment of the Analog. Dramatic increases in fitness revealed in the Host to Coast Ana- log due to evolutionary exposure to alkalinity and cycling pH suggested that these factors are critically important in the evolutionary ecology of E. coli. Evolv- ing the capacity for seawater survival and growth, combined with increased capability to infect human hosts, could facilitate E. coli infection from seawater exposure. Results suggest implications for wastewater management in order to prevent superior strains of pathogenic E. coli from evolving.