pneumonia

EuroPneumo Special Issue / pneumonia 2015 Oct 21;7:I–72
O2.2
Competence for genetic transformation in Streptococcus pneumoniae:
primary sigma factor mutations enhance transcription of late genes in
comW mutants
Yanina Tovpeko, Donald A. Morrison
Molecular, Cell, and Developmental Biology, Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
Streptococcus pneumoniae is naturally transformable, but the mechanism governing transformation is not fully
understood. Streptococcal transformation depends on transient accumulation of high levels of the alternative sigma
factor σ X , coordinated via peptide pheromones. σ X recognises a non-canonical promoter upstream of late competence
genes, including those required for DNA uptake. However, full competence also requires a second competence-specific
protein, ComW, regulated by the same pheromone circuit as σ X . We mapped 27 independent comW bypass mutations to
10 single-base transitions, all within rpoD, encoding the primary sigma, σ A . σ A* mutants transformed at an elevated rate
(1% to 20% of WT), far above the comW rate (0.01%). Eight σ A* proteins carried altered residues in RpoD region, 4 that
are implicated in interaction of σ A with the core β subunit. To test for a role for comW in RNAP function, we measured
the effect of the suppressor mutations on late gene expression. Late gene expression was restored to 30% to 80% of
WT levels in the σ A* mutant strains, compared to only 10% in the comW mutant, consistent with the idea that ComW
increases σ X access to core RNAP, and with the location of the mutations in the protein structure. While σ X activity was
restored to 80% of the WT level in one σ A* mutant, the amount of transformants reached only 10% of the WT level,
indicating an additional role of ComW in the development of competence distinct from its role in transcription of late
genes.
Supported by NSF Grant. (MCB-1020863)
O2.3
A new role for Autoinducer-2 in Streptococcus pneumoniae
Claudia Trappetti 1 , Bart Eijkelkamp 1 , Zarina Amin 1 , Adrienne Paton 1 , Christopher McDevitt 1 ,
Marco Oggioni 2 , James Paton 1
1
University of Adelaide, Adelaide, Australia; 2 University of Leicester, Leicester, UK
Bacteria are able to survive in their environment by developing complex multicellular communities, rather than
functioning as individual cells. Communication between cells is essential and is achieved by the secretion and
detection of small signalling molecules called autoinducers. To date, the only signalling molecule recognised by
both Gram-positive and Gram-negative bacteria is the Autoinducer-2 (AI-2). AI-2 is synthesised by the metabolic
enzyme LuxS (S–ribosyl–homocysteine lyase) as a by-product of the conversion of S–ribosyl–homocysteine into
homocysteine. Homologues of LuxS have been found in all bacterial species, suggesting a key role in interspecies
communication. The data presented here indicate that in Streptococcus pneumoniae, AI-2 accelerates and modulates
the progression of disease in mice. In this study, we determined whether the known reduced virulence of a luxS
mutant relative to its wild-type parent D39, could be restored by administrating purified AI-2 in a murine model.
Mice were challenged intranasally with either wild-type or luxS mutant strains and AI-2 was administrated at time zero
and 24 hours post-infection. Treatment with AI-2 significantly increased the levels of bacteraemia and lung invasion in
mice challenged with the luxS mutant. Moreover, the rate of survival was dramatically reduced and the virulence of the
luxS mutant could be reconstituted to the same level of the wild-type strain. To further investigate whether AI-2 could
modulate innate immune responses in the host, we performed a RNA-cytokine array. Surprisingly, we found that only
one cytokine receptor was differentially expressed between groups of mice challenged with either wild-type or luxS
mutant, and that the expression level of this cytokine could be restored if AI-2 is administrated. These data provide
evidence that AI-2 is critical for S. pneumoniae to modulate host immune responses in order to induce systemic disease.
Thus, an inhibitor of the universal signal molecule could have therapeutic potential.
pneumonia 2015 Volume 7
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