Swarming

It is known that Bacillus subtilis (strain 168) which is generally used in the lab is unable to swarm on a solid surface eg. agar plate. This is because of two reasons which are:

1. Surfactin is a natural surfactant which helps in reducing surface tension and aids the bacteria to swarm on a solid or semi solid medium. Strain 168 is unable to produce the bacterial cyclic lipopeptide surfactin.
2. Strain 168 is also unable to bio synthesize flagellum and thus has a very low amount of swarming.

sfp

Strain 168 is unable to produce surfactin because it contains a frameshift mutation in the gene named sfp. In a non domisticated strain 3610, sfp gene is intact and thus produces a protein which helps in the post translational modification of the immature surfactin peptide formed by the srfABCD operon. After the modification, this peptide is exported out of the cell and helps in breaking the surface tension and aids the movement of the bacteria.

swrA

In the undomesticated strain 3610, the gene swrA along with the gene swrB helps in the bio synthesis of flagellum. swrA acts on the the gene sigD which acts as a transcription for the genes required in the late flagellum biosynthesis. The laboratory strain 168 contains a fameshift mutation in the gene swrA and thus the stain moves on the surface with a very slow pace.

swrC

It provides resistance to the antimicrobial action of the peptide surfactin.

efp

efp stands for Elongation Factor P and this gene helps in the non dendritic swarming.

Pathway

Swarming of the colony cells starts when the concentration of the signalling peptide ComX and the pentapeptide pheromone CSF (encodede by phrC) reach a critical concentration and activates the sensor kinase ComP by phosphorylating it. ComP is a part of two component transduction system and thus activates response regulator ComA which is present downstream to ComP.

ComA targets srf operon which consists of four genes viz srf A,B,C, and D and it also targets ComS which is present upstream to the srf operon and it activates competence by displacing MecA from ComK and thus MecA is targeted for proteolysis by ClpC/ClpB. ComK regulates the genes required for competence.

While ComA is activating srf operon, another gene named sfp encodes 4' phosphopantetheinyl transferase which is required to activate each of the four surfactin synthases by the post translational modification of Srf A, Srf B, Srf C, and Srf D, which are required for the non ribosomal assembly of the surfactin heptapeptide.

Simultaneously, gene swrA activates the transcription factor sigD (sigma D) which acts on the genes required in the late flagellum biosynthesis.

Bibliography

1. Julkowska, D, Obuchowski, M, Holland, IB & Se, SJ 2005, "Comparative Analysis of the Development of Swarming Communities of Bacillus subtilis 168 and a Natural Wild Type : Critical Effects of Surfactin and the Composition of the Medium." Society, vol. 187, no. 1, pp. 65-76.
2. Kearns, DB & Losick, R 2004, "Swarming motility in undomesticated Bacillus subtilis." Molecular Microbiology, vol. 49, no. 3, pp. 581-590.
3. Kearns, DB, Chu, F, Rudner, R & Losick, R 2004, "Genes governing swarming in Bacillus subtilis and evidence for a phase variation mechanism controlling surface motility." Molecular microbiology, vol. 52, no. 2, pp. 357-69.