A non-flagellated biocontrol bacterium employs a PilZ-PilB complex to provoke twitching motility associated with its predation behavior

Abstract

Lysobacter enzymogenes OH11 is a non-flagellated, ubiquitous soil bacterium with broad-spectrum antifungal activities. Although lacking flagella, it employs another type of motile behavior, known as twitching motility that is powered by type IV pilus (T4P) to move towards neighboring crop fungal pathogens to kill them as food. At present, little is known about how this non-flagellated bacterium controls twitching motility that is crucial for its predatory lifestyle. Herein, we present a report on how a non-canonical PilZ domain, PilZ Le3639 , controls such motility in the non-flagellated L. enzymogenes ; it failed to bind with c-di-GMP but seemed to be required for twitching motility. Using bacterial two-hybrid and pull-down approaches, we identified PilB Le0708 , one of the PilZ Le3639 -binding proteins that are essential for the bacterial twitching motility, could serve as an ATPase to supply energy for T4P extension. Through site-mutagenesis approaches, we identified one essential residue of PilZ Le3639 that is required for its binding affinity with PilB Le0708 and its regulatory function. Besides, two critical residues within the ATPase catalytic domains of PilB Le0708 were detected to be essential for regulating twitching behavior but not involved in binding with PilZ Le3639 . Overall, we illustrated that the PilZ-PilB complex formation is indispensable for twitching motility in a non-flagellated bacterium.