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.