C, Box and whisker plots showing mean pixel intensities for ColE9* K469CAF647 fluorescence per cell measured for the indicated cells and condition used, whiskers represent minimum and maximum mean pixel intensity, box shows 1st and 3rd quartile with the median shown as a line. From left-to-right: E. coli JM83 cells; E. coli btuB deletion strain showing loss of all ColE9* K469CAF647 cell-associated fluorescence; E. coli JM83 cells in the presence of CCCP; E. coli JM83 cells following trypsin treatment showing significant ColE9* K469CAF647 fluorescence remains associated with cells indicative of import; E. coli JM83 cells treated with CCCP and trypsin showing the complete loss of internalised ColE9* K469CAF647 fluorescence. n, number of cells used, typically from 2-4 biological replicates. ****, indicates a t value <0.05 in a student T-test as a statistically significant result, ns indicates no significant difference as determined by student T-test. 