Neisseria meningitidis is a Gram-negative human-restricted
pathogen that asymptomatically resides in the human respiratory
tract. Meningococcal meningitis and sepsis both are
caused by N. meningitidis. The bacterium must adhere to host
epithelial cells in order to colonize effectively. The factors that
determine the initial attachment to the host and dispersal, are
not well understood. Metabolites released by the host may aid
in meningococcal colonization and dissemination. Polyamines
are aliphatic polycations that assist in cell survival and proliferation.
The virulence properties of N. meningitidis after
exposure to polyamines were investigated. Adhesion to nasopharyngeal
epithelial cells increased in the presence of spermine.
Also, the relative expression of adhesin, pilE increased
in the presence of spermine. Further, relative expression of
ctrA, ctrB and lipB was upregulated in the presence of spermidine,
indicating increased capsule formation. Upregulated
capsule synthesis of N. meningitidis in the presence of spermidine
allows it to survive in murine macrophages. The study
suggests the importance of the extracellular pool of polyamines
in promoting virulence in N. meningitidis.
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The catA gene encodes the major catalase in Streptomyces coelicolor, whose production increases upon H_2O_2 treatment. Besides the previously identified primary promoter (catAp1), a minor promoter (catAp2) was newly assigned by S1 nuclease mapping. The catAp2 transcript was observed transiently upon entry into the stationary phase in liquid culture and upon differentiation on solid plates, whereas the level of catAp1 transcription did not change significantly during this growth transition. The catAp1 promoter was transcribed by the major vegetative RNA polymerase holoenzyme containing [sigma]^HrdB , whereas the catAp2 was transcribed in vitro by the holoenzyme containing [sigma]^R that is activated under oxidative conditions. The cis-element regulating the H_2 O_2 -inducibility of catAp1 was identified within the 23 bp inverted repeat sequence located between -65 and -43 of the catAp1 promoter. We named this sequence HRE (H_2O_2 -responsive element). The distal half of the inverted repeat was more crucial for H_2 O_2 ?pendent induction of the catAp1 transcript than the proximal half. HRE most likely serves as a binding site for the H_2 O_2 -responsive repressor CatR.