Extracellular Proteolytic Activity Plays a Central Role in Swarming Motility inBacillus subtilis

Abstract

Natural isolates of Bacillus subtilis exhibit a robust multicellular behavior known as swarming. A form of motility, swarming is characterized by a rapid, coordinated progression of a bacterial population across a surface. As a collective bacterial process, swarming is often associated with biofilm formation and has been linked to virulence factor expression in pathogenic bacteria. While the swarming phenotype has been well documented for Bacillus species, an understanding of the molecular mechanisms responsible remains largely isolated to gram-negative bacteria. To better understand how swarming is controlled in members of the genus Bacillus, we investigated the effect of a series of gene deletions on swarm motility. Our analysis revealed that a strain deficient for the production of surfactin and extracellular proteolytic activity did not swarm or form biofilm. While it is known that surfactin, a lipoprotein surfactant, functions in swarming motility by reducing surface tension, this is the first report demonstrating that general extracellular protease activity also has an important function. These results not only help to define the factors involved in eliciting swarm migration but support the idea that swarming and biofilm formation may have overlapping control mechanisms.It has long been recognized that bacteria can facilitate their growth and survival by forming cooperative, multicellular communities that are most often associated with surfaces (38). Such organized populations of microorganisms have been found in both clinical and environmental settings, where they have positive and negative impacts on human health and environmental ecology (4, 24). For these reasons, bacterial multicellularity is being actively studied, and while biofilms are most commonly ascribed to this type of behavior, swarming is another primary example of a surface-associated collective bacterial process. A form of migration, swarming facilitates the rapid colonization of surfaces by a population of bacteria. Swarming motility has been linked with biofilm formation, antibiotic resistance, and virulence factor production (1, 21, 39). Many of the virulence factors reported to be associated with the occurrence of swarming are exoenzymes and, more specifically, extracellular proteases (12, 47). While a strong link between swarming, extracellular protease production, and pathogenesis has been noted (12,44,47), only a few studies have focused on the requirement of proteases for swarm motility. In a recent investigation, the extracellular protease Epr was found to be essential for swarming motility in the domesticated Bacillus subtilis laboratory strain 168 (6). Since laboratory strains of B. subtilis have been shown to exhibit less-robust biofilm formation and swarm motility (3, 20), we were interested in investigating whether Epr and other extracellular proteases were involved in swarming in an undomesticated B. subtilis strain.First described more than a century ago for the gram-negative organism Proteus, swarming motility has now been...

A Halotolerant Bacterium Bacillus licheniformis HSW-16 Augments Induced Systemic Tolerance to Salt Stress in Wheat Plant (Triticum aestivum)

“…Therefore, test organism was tested for its motility following the standard protocol of Connelly et al (2004).…”

Bacterial swarming: a model system for studying dynamic self-assembly

“…91–93 Kearns and Losick discovered that surfactin was essential for swarming migration in B. subtilis . 48 Laboratory strains of B. subtilis that do not swarm contain a frameshift mutation in the sfp gene required for surfactin synthesis.…”

Maturation of Fibrinolytic Bacillopeptidase F Involves both Hetero- and Autocatalytic Processes

“…The principal function of extracellular proteases, including Bpr, is thought to be supplying nutrients for bacterial growth by degrading extracellular proteins, although additional physiological functions have also been described for some of these proteases. For instance, Epr (40) and Vpr (41,42) are involved in swarming motility of B. subtilis. AprE, WprA, and Vpr are reported to play a role in processing and activation of the antibiotic peptide subtilin, and a function for Bpr and Epr in this process cannot be ruled out (43).…”