Loss of FliL Alters Proteus mirabilis Surface Sensing and Temperature-Dependent Swarming

Abstract

Proteus mirabilis is a dimorphic motile bacterium well known for its flagellum-dependent swarming motility over surfaces. In liquid, P. mirabilis cells are 1.5-to 2.0-m swimmer cells with 4 to 6 flagella. When P. mirabilis encounters a solid surface, where flagellar rotation is limited, swimmer cells differentiate into elongated (10-to 80-m), highly flagellated swarmer cells. In order for P. mirabilis to swarm, it first needs to detect a surface. The ubiquitous but functionally enigmatic flagellar basal body protein FliL is involved in P. mirabilis surface sensing. Previous studies have suggested that FliL is essential for swarming through its involvement in viscosity-dependent monitoring of flagellar rotation. In this study, we constructed and characterized ⌬fliL mutants of P. mirabilis and Escherichia coli. Unexpectedly and unlike other fliL mutants, both P. mirabilis and E. coli ⌬fliL cells swarm (Swr ؉ ). Further analysis revealed that P. mirabilis ⌬fliL cells also exhibit an alteration in their ability to sense a surface: e.g., ⌬fliL P. mirabilis cells swarm precociously over surfaces with low viscosity that normally impede wild-type swarming. Precocious swarming is due to an increase in the number of elongated swarmer cells in the population. Loss of fliL also results in an inhibition of swarming at <30°C. E. coli ⌬fliL cells also exhibit temperature-sensitive swarming. These results suggest an involvement of FliL in the energetics and function of the flagellar motor. Most bacteria are able to live a planktonic free-living lifestyle or in a surface-attached microbial community called a "biofilm." The interchange between the motile and the sessile phases, referred to as the "swim-or-stick" switch, is not merely stochastic. Rather, the lifestyle change occurs in response to cues that a cell senses as it nears a surface (1). These surface signals are required and initiate biofilm formation (1). A fundamental question underlying the transition in lifestyle from motile to sessile phases is how does a bacterium sense a surface?Studies of many different bacterial species support the idea that surface sensing often involves the bacterial flagellum (2), which also facilitates movement toward and attachment to a surface. However, it is generally agreed that motility and biofilm formation are mutually exclusive. Moreover, flagella are used not only for swimming in liquid but also for swarming over a solid surface. Many bacterial species swarm, and often, as in Proteus mirabilis, require a surface-induced differentiated cell type, called a swarmer cell, that is elongated and hyperflagellated (3).P. mirabilis is a Gram-negative gammaproteobacterium belonging to the Enterobacteriaceae family. It is an opportunistic pathogen capable of causing urinary tract infections (UTI) (4-6). P. mirabilis is dimorphic and produces short vegetative swimmer cells (1.5 to 2.0 m in length) with a single nucleoid and 4 to 10 peritrichous flagella when cultured in nutrient broth. Conversely, when cultured on nutrient agar or in viscous en...

Imaging the Motility and Chemotaxis Machineries in Helicobacter pylori by Cryo-Electron Tomography

“…The location and structure of the additional ring are similar to those of the FliL ring found in B. burgdorferi (43,44). FliL has been shown to play important but diverse roles in many bacterial species (43,(45)(46)(47). The exact structure and function of FliL in H. pylori remain to be elucidated.…”

Proteomics of Colwellia psychrerythraea at subzero temperatures – a life with limited movement, flexible membranes and vital DNA repair

“…In addition, one flagellum-related protein was more abundant at −10°C 8 weeks: FliL ( Fig. Further, they demonstrated that the motility of ΔfliL is temperature dependent, suggesting that FliL interacts with a component of the motor involved in torque generation and helps maintain the integrity and stability of the flagellar rod (Lee and Belas, 2014). FliL is proposed to participate in the coupling of MotB with the flagellar rotor in an indirect fashion and is part of the basal flagellum complex (Suaste-Olmos et al, 2010).…”

“…revealed that FliL plays a role in sensing surfaces (Lee et al, 2013). Further, they demonstrated that the motility of ΔfliL is temperature dependent, suggesting that FliL interacts with a component of the motor involved in torque generation and helps maintain the integrity and stability of the flagellar rod (Lee and Belas, 2014). Because fliL defects yield species-specific phenotypic changes (Lee et al, 2013 and refs within), the exact role of the increased abundance of FliL in −10°C Cp34H cells needs to be examined further.…”

Swarming bacteria respond to increasing barriers to motility by increasing cell length and modifying colony structure

“…We further propose that novel and yet uncharacterized mechanisms exist to tune swarmer cell elongation and promote multicellular rafting based on integrated environmental cues. The motA-deficient strain failed to elongate, and flagellar activity is linked to swarmer cell development (40). Therefore, such unidentified mechanisms presumably function downstream of a theorized flagella-mediated surface-sensing switch.…”