Characterization of the Dapa-Nlpb Genetic Locus Involved in Regulation of Swarming Motility, Cell Envelope Architecture, Hemolysin Production, and Cell Attachment Ability in Serratia Marcescens
Resource
INFECTION AND IMMUNITY v.73 n.9 pp.6075-6084
Journal
INFECTION AND IMMUNITY
Journal Volume
v.73
Journal Issue
n.9
Pages
6075-6084
Date Issued
2005
Date
2005
Author(s)
Soo, P.-C.
Wei, J.-R.
Horng, Y.-T.
Hsieh, S.-C.
Ho, S.-W.
Lai, H.-C.
Abstract
Swarming migration of Serratia marcescens requires both flagellar motility and cellular differentiation and is a population-density- dependent behavior. While the flhDC and quorum-sensing systems have been characterized as important factors regulating S. marcescens swarming, the underlying molecular mechanisms are currently far from being understood . Serratia swarming is thermoregulated and is characterized by continuous surface migration on rich swarming agar surfaces at 30°C but not at 37°C . To further elucidate the mechanisms, identification of specific and conserved regulators that govern the initiation of swarming is essential. We performed transposon mutagenesis to screen for S. marcescens strain CH- 1 mutants that swarmed at 37°C. Analysis of a "precocious-swarming" mutant revealed that the defect in a conserved dapASm-nlpBSm genetic locus which is closely related to the synthesis of bacterial cell wall peptidoglycan is responsible for the aberrant swarming phenotype. Further complementation and gene knockout studies showed that nlpBSm, which encodes a membrane lipoprotein, NlpBSm, but not dapASm, is specifically involved in swarming regulation. On the other hand, dapASm but not nlpBSm is responsible for the determination of cell envelope architecture, regulation of hemolysin production, and cellular attachment capability. While the nlpBSm mutant showed similar cytotoxicity to its parent strain, the dapASm mutant significantly increased in cytotoxicity. We present evidence that DapASm is involved in the determination of cell-envelope- associated phenotypes and that NlpBSm is involved in the regulation of swarming motility.