In our previous study [Hong Y, Brown DG (2009) Appl Environ Microbiol 75(8):2346-2353], the adenosine triphosphate (ATP) level of adhered bacteria was observed to be 2-5 times higher than that of planktonic bacteria. Consequently, the proton motive force (Delta p) of adhered bacteria was approximately 15% greater than that of planktonic bacteria. It was hypothesized that the cell surface pH changes upon adhesion due to the charge-regulated nature of the bacterial cell surface and that this change in surface pH can propagate to the cytoplasmic membrane and alter Delta p. In the current study, we developed and applied a charge regulation model to bacterial adhesion and demonstrated that the charge nature of the adhering surface can have a significant effect on the cell surface pH and ultimately the affect the ATP levels of adhered bacteria. The results indicated that the negatively charged glass surface can result in a two-unit drop in cell surface pH, whereas adhesion to a positively charged amine surface can result in a two-unit rise in pH. The working hypothesis indicates that the negatively charged surface should enhance Delta p and increase cellular ATP, while the positively charged surface should decrease Delta p and decrease ATP, and these results of the hypothesis are directly supported by prior experimental results with both negatively and positively charged surfaces. Overall, these results suggest that the nature of charge on the solid surface can have an impact on the proton motive force and cellular ATP levels.
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