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Microbiology 155 (2009), 912-921; DOI  10.1099/mic.0.021741-0
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Microbiology 155 (2009), 912-921; DOI  10.1099/mic.0.021741-0
© 2009 Society for General Microbiology

Identification of non-flagellar genes involved in swarm cell differentiation using a Bacillus thuringiensis mini-Tn10 mutant library

Sara Salvetti1, Francesco Celandroni1, Mara Ceragioli2, Sonia Senesi2 and Emilia Ghelardi1

1 Dipartimento di Patologia Sperimentale, Biotecnologie Mediche, Infettivologia ed Epidemiologia, Università di Pisa, via San Zeno 35-39, 56127 Pisa, Italy
2 Dipartimento di Biologia, Sezione di Microbiologia, Università di Pisa, via San Zeno 35-39, 56127 Pisa, Italy

Correspondence
Emilia Ghelardi
ghelardi{at}biomed.unipi.it

Swarming is a social phenomenon that enables motile bacteria to move co-ordinately over solid surfaces. The molecular basis regulating this process is not completely known and may vary among species. Insertional mutagenesis of a swarming-proficient Bacillus thuringiensis strain was performed, by use of the transposon mini-Tn10, to identify novel genetic determinants of swarming that are dispensable for flagellation, swimming motility, chemotaxis and active growth. Among the 67 non-swarming mutants obtained, six were selected that showed no defect in flagellar assembly and function, chemotaxis or growth rate. Sequence analysis of DNA flanking the transposon insertion led to the identification of previously uncharacterized genes that are involved in the development of swarming colonies by B. thuringiensis and that are highly conserved in all members of the Bacillus cereus sensu lato group. These genes encode non-flagellar proteins with putative activity as sarcosine oxidase, catalase-2, amino acid permease, ATP-binding cassette transporter, dGTP triphosphohydrolase and acetyltransferase. Functional analysis of two of the isolated mutants demonstrated that swarming differentiation depends on the intracellular levels of the osmoprotectant glycine betaine and on the quantity of synthesized phenazine secondary metabolites. The finding that proteins involved in diverse physiological processes have a role in swarming motility underlines the complexity of the molecular mechanisms governing this behaviour in B. thuringiensis.

Abbreviations: AHL, N-acylhomoserine lactone; Tgen, generation time; CI, chemotaxis index; PZ, phenazine






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Copyright © 2009 Society for General Microbiology.