Surveying a Swarm: Experimental Techniques To Establish and Examine Bacterial Collective Motion

The survival and successful spread of many bacterial species hinges on their mode of motility. One of the most distinct of these is swarming, a collective form of motility where a dense consortium of bacteria employ flagella to propel themselves across a solid surface. Surface environments pose unique challenges, derived from higher surface friction/tension and insufficient hydration. Bacteria have adapted by deploying an array of mechanisms to overcome these challenges. Beyond allowing bacteria to colonize new terrain in the absence of bulk liquid, swarming also bestows faster speeds and enhanced antibiotic resistance to the collective. These crucial attributes contribute to the dissemination, and in some cases pathogenicity, of an array of bacteria. This minireview highlights (i) aspects of swarming motility that differentiate it from other methods of bacterial locomotion, (ii) facilitatory mechanisms deployed by diverse bacteria to overcome different surface challenges, (iii) the (often difficult) approaches required to cultivate genuine swarmers, (iv) the methods available to observe and assess the various facets of this collective motion, and (v) the features exhibited by the population as a whole.