Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2007
Publication Date: 3/13/2008
Citation: Haznedaruglu, B.Z., Bolster, C.H., Walker, S.L. 2008. The Role of Starvation on Escherichia coli Adhesion and Transport in Saturated Porous Media. Water Research. Vol 42 pp 1547-1554 Interpretive Summary: Interpretative Summary: Escherichia coli (E. coli) is commonly used as an indicator of fecal pollution. Therefore, it is important to have a good understanding of how this microorganism moves in the environment. Cell surface characteristics such as surface charge and hydrophobicity have been shown to play an important role controlling microbial movement in the environment. What is not well known is how these surface characteristics are affected by the starvation status of the cells. Therefore, we conducted a series of surface characterizations and transport experiments with two E. coli isolates that were starved for 0, 6, 12, and 18 hours. Our findings show that hydrophobicity, surface charge, size, and presence and composition of extracellular polymers depended strongly on the starvation status of the cells. We also found that the transport behavior of the cells through a packed-bed column varied depending on starvation status but the variation was not well correlated with the observed variations in cell surface characteristics. This study highlights the importance of consistency in bacterial preparation for transport and characterization studies and has considerable implications for the future evaluation and prediction of E. coli fate in subsurface environments.
Technical Abstract: The influence of bacterial starvation on cell fate and transport has been examined using two Escherichia coli isolates: one human isolate (HU) and one dairy cow isolate (DC). To better understand the transport of starved bacteria, deposition experiments were conducted in a packed bed column system using cells that had been incubating at room temperature without nutrients for 6, 12, and 18 hour periods as well as time zero harvested, non-starved cells. Complimentary cell characterization techniques were conducted in combination with the transport experiments to evaluate the hydrophobicity, electrophoretic mobility, size, and surface charge density of the cells at the starvation conditions considered. It was observed that the HU cells at time zero were more adhesive than cells starved for longer periods of time. This behavior is attributed to the relatively high hydrophobicity, which resulted from greater extracellular polymeric substance (EPS) presence. The DC cells were most adhesive at time zero and least adhesive after 18 hours of starvation, although cell characterization results (notably the hydrophobicity) did not correlate to transport trends like the HU cells. For both isolates, after 6 hours of starvation the cells exhibited unexpected transport trends and high levels of sugars to proteins in the EPS. Our results suggest transport behavior of environmental E. coli isolates differ in terms of isolate host and starvation conditions. Possible mechanisms responsible for this phenomenon are changes in key cell surface characteristics and synthesis of starvation induced proteins. This study highlights the importance of consistency in bacterial preparation for transport and characterization studies and has considerable implications for the future evaluation and prediction of E. coli fate in subsurface environments.