Abstract
Bacteria have developed various motility mechanisms to adapt to a variety of solid surfaces. A rhizosphere isolate, Paenibacillus sp. NAIST15-1, exhibited unusual motility behavior. When spotted onto 1.5% agar media, Paenibacillus sp. formed many colonies, each of which moved around actively at a speed of 3.6 μm/sec. As their density increased, each moving colony began to spiral, finally forming a static round colony. Despite its unusual motility behavior, draft genome sequencing revealed that both the composition and organization of flagellar genes in Paenibacillus sp. were very similar to those in Bacillus subtilis. Disruption of flagellar genes and flagellar stator operons resulted in loss of motility. Paenibacillus sp. showed increased transcription of flagellar genes and hyperflagellation on hard agar media. Thus, increased flagella and their rotation drive Paenibacillus sp. motility. We also identified a large extracellular protein, CmoA, which is conserved only in several Paenibacillus and related species. A cmoA mutant could neither form moving colonies nor move on hard agar media; however, motility was restored by exogenous CmoA. CmoA was located around cells and enveloped cell clusters. Comparison of cellular behavior between the wild type and cmoA mutant indicated that extracellular CmoA is involved in drawing water out of agar media and/or smoothing the cell surface interface. This function of CmoA probably enables Paenibacillus sp. to move on hard agar media.
Highlights
Migration is a critical mechanism by which bacteria survive and thrive in a particular environment
Motility is crucial as it enables bacteria to seek out and colonize suitable environments
Our isolate Paenibacillus sp. was suitable for the analysis because it was amenable to genetic manipulation (Methods, see below)
Summary
Migration is a critical mechanism by which bacteria survive and thrive in a particular environment. The organelles responsible for mobility, flagella, are common in bacteria [1]. The most common form of flagella-dependent motility, called swimming motility, only works in an aqueous environment. Bacteria live in aqueous environments and on a variety of biotic and abiotic solid surfaces. Many bacteria have developed mechanisms that facilitate movement on a solid surface. These include swarming, twitching, gliding, and sliding motility, which are mediated by flagella, Type IV pili, focal adhesion complexes, surface active molecules, or the expansive forces generated by growing cells [2,3,4]
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