A view to a kill: using cutting edge microscopy to study predatory bacteria

Bdellovibrio bacteriovorus (B. bacteriovorus) are a promising tool in the fight against antimicrobial resistance. With a predatory lifestyle and a wide range of prey, including antibiotic drug resistant pathogens, they are novel solution to the growing issues presented by antimicrobial resistant bacteria. Despite the proven importance of motility to B. bacteriovorus predation efficiency, their swimming behaviour remained little understood. The key characteristics of their motility including their re-orientation mechanisms were unknown. This study has utilised digital inline holographic microscopy (DIHM), a novel three-dimensional and high speed imaging technique, to shed new light on B. bacteriovorus swimming behaviour. The cells were tracked in a range of conditions including in bulk fluid, near to surfaces and in the presence of live prey cells. The resulting trajectories were analysed to quantify the key motility characteristics, patterns, and differences in behaviour dependent on condition changes. I have shown, for the first time, that B. bacteriovorus have a complex bi-phasic swimming style with run-reverse-flick re-orientations. Their motility behaviour including swimming speeds, run lengths and re-orientation angles remains consistent over a co-culturing window of 19-24 hours. However, it changes radically near to surfaces showing a significant drop in swimming speed and no longer performing a run reverse flick style re-orientation. Instead, its behaviour becomes significantly more homogeneous in both run length distribution and re-orientation angle. In contrast, in the presence of live prey cells B. bacteriovorus retain the run reverse flick behaviour but increase their swimming speed. This is likely a mechanism to increase predation efficiency in areas of high prey density. These results represents the first in-depth three-dimensional study of B. bacteriovorus motility.