Quantitative changes in the elasticity and adhesive properties of Escherichia coli ZK1056 prey cells during predation by Bdellovibrio bacteriovorus 109J

Atomic force microscopy (AFM) was used to explore the changes that occur in Escherichia coli ZK1056 prey cells while they are being consumed by the bacterial predator Bdellovibrio bacteriovorus 109J. Invaded prey cells, called bdelloplasts, undergo substantial chemical and physical changes that can be directly probed by AFM. In this work, we probe the elasticity and adhesive properties of uninvaded prey cells and bdelloplasts in a completely native state in dilute aqueous buffer without chemical fixation. Under these conditions, the rounded bdelloplasts were shown to be shorter than uninvaded prey cells. More interestingly, the extension portions of force curves taken on both kinds of cells clearly demonstrate that bdelloplasts are softer than uninvaded prey cells, reflecting a decrease in bdelloplast elasticity after invasion by Bdellovibrio predators. On average, the spring constant of uninvaded E coli cells (0.23 +/- 0.02 N/m) was 3 times stiffer than that of the bdelloplast (0.064 +/- 0.001 N/m) when measured in a HEPES - metals buffer. The retraction portions of the force curves indicate that compared to uninvaded E. coli cells bdelloplasts adhere to the AFM tip with much larger pull-off forces but over comparable retraction distances. The strength of these adhesion forces decreases with increasing ionic strength, indicating that there is an electrostatic component to the adhesion events.