Identification of genes required for different stages of dendritic swarming in Bacillus subtilis, with a novel role for phrC.
Highly branched dendritic swarming of B. subtilis on synthetic B-medium involves a developmental-like process that is absolutely dependent on flagella and surfactin secretion. In order to identify new swarming genes, we targeted the two-component ComPA signalling pathway and associated global regulators. In liquid cultures, the histidine kinase ComP, and the response regulator ComA, respond to secreted pheromones ComX and CSF (encoded by phrC) in order to control production of surfactin synthases and ComS (competence regulator). In this study, for what is believed to be the first time, we established that distinct early stages of dendritic swarming can be clearly defined, and that they are amenable to genetic analysis. In a mutational analysis producing several mutants with distinctive phenotypes, we were able to assign the genes sfp (activation of surfactin synthases), comA, abrB and codY (global regulators), hag (flagellin), mecA and yvzB (hag-like), and swrB (motility), to the different swarming stages. Surprisingly, mutations in genes comPX, comQ, comS, rapC and oppD, which are normally indispensable for import of CSF, had only modest effects, if any, on swarming and surfactin production. Therefore, during dendritic swarming, surfactin synthesis is apparently subject to novel regulation that is largely independent of the ComXP pathway; we discuss possible alternative mechanisms for driving srfABCD transcription. We showed that the phrC mutant, largely independent of any effect on surfactin production, was also, nevertheless, blocked early in swarming, forming stunted dendrites, with abnormal dendrite initiation morphology. In a mixed swarm co-inoculated with phrC sfp+ and phrC+ sfp (GFP), an apparently normal swarm was produced. In fact, while initiation of all dendrites was of the abnormal phrC type, these were predominantly populated by sfp cells, which migrated faster than the phrC cells. This and other results indicated a specific migration defect in the phrC mutant that could not be trans-complemented by CSF in a mixed swarm. CSF is the C-terminal pentapeptide of the surface-exposed PhrC pre-peptide and we propose that the residual PhrC 35 aa residue peptide anchored in the exterior of the cytoplasmic membrane has an apparently novel extracellular role in swarming.
Hamze
Kassem
K
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Julkowska
Daria
D
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Autret
Sabine
S
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Hinc
Krzysztof
K
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Nagorska
Krzysztofa
K
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Sekowska
Agnieszka
A
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Holland
I Barry
IB
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
Séror
Simone J
SJ
Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
D001412:Bacillus subtilis / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D001426:Bacterial Proteins; C061262:ComA protein, Bacteria; D004268:DNA-Binding Proteins; C101115:PhrC protein, Bacillus subtilis; D012097:Repressor Proteins