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Two Best Poster Prizes for Microbiology

ITQB PhD students work recognized at Microbiotec'11

Oeiras, 06.11.2011

Two ITQB PhD students, Catarina S. Pereira and Mafalda Xavier Henriques, received Best Poster Presentation Prizes at the MICROBIOTEC’11, which took place last week in Braga.

MICROBIOTEC is a national congress jointly organized by the Portuguese Society for Microbiology and the Portuguese Society for Biotechnology. MICROBIOTEC’11 Best Poster Presentation Prizes were attributed by both societies to award the best poster presentation within each one of the ten MICROBIOTEC´11 poster sessions.

Catarina S. Pereira from the Bacterial Signalling Lab (ITQB/IGC) presented her poster entitled "Phosphoenolpyruvate phosphotransferase system regulates detection and processing of the quorum sensing signal Autoinducer-2" at the Molecular Microbiology and Microbial Physiology Symposium. This poster was also awarded with the Best Poster Prize, attributed by The Portuguese Society for Microbiology and sponsored by The American Society for Microbiology to the best poster contribution on Microbiology Research in MICROBIOTEC’11 .

Mafalda Xavier Henriques from the Bacterial Cell Surfaces and Pathogenesis Lab presented her poster entitled “Synthesis of capsular polysaccharide at the divsision septum of Streptococcus pneumoniae is dependent on a bacterial tyrosine kinase” at the Cellular Microbiology and Pathogenesis Symposium.


Poster Abstracts

Phosphoenolpyruvate phosphotransferase system regulates detection and processing of the quorum sensing signal Autoinducer-2

C. S. Pereira, A. J. Santos, P. B. Correia and K. B. Xavier

Certain bacteria can interfere with quorum sensing-regulated behaviors of neighboring species by internalizing the signal AI-2 using the Lsr transport system (encoded by the lsr operon). Here we show that the phosphoenolpyruvate phosphotransferase system (PTS) is required for Lsr activation and is essential for AI-2 internalization.
Our results suggest that AI-2 internalization is initiated by a PTS-dependent mechanism, which provides sufficient intracellular AI-2 to relieve repression of the lsr operon and, thus induce depletion of
AI-2 from the extracellular environment. The fact that AI-2 internalization is not only controlled by the community-dependent accumulation of AI-2, but also depends on the phosphorylation state of PTS suggests that Escherichia coli can integrate information on the availability of substrates with external communal information to control quorum sensing and its interference.


Synthesis of capsular polysaccharide at the divsision septum of Streptococcus pneumoniae is dependent on a bacterial tyrosine kinase

M. X. Henriques, T. Rodrigues, M. Carido, L. Ferreira and S. R. Filipe

Streptococcus pneumoniae is an important Gram-positive pathogen, associated with a variety of infections that can range in severity from otitis media to pneumonia or meningitis. It is a frequent cause of community-acquired pneumonia in developed countries, with mortality rates higher than 20% in patients presenting concurrent septicemia. In developing countries, 25% of all preventable deaths in children under the age of 5 are due to pneumococcal septicemia.
Pneumococcal cells possess a capsular polysaccharide (capsule or CPS) surrounding its entire surface. This strucutre plays a major role both in the colonization and in the persistence of the bacteria in the infected host, conferring protection against its innate immune system. There are currently known more than 90 differente types of CPS, or serotypes, but in almost all of them the genes that code for proteins involved in the synthesis and regulation of the capsule are located at the same chromosomal region, the cps operon. This operon is constituted by serotype specific genes, that encode proteins required for the syntesis of the specific sugar components of each capsular polysaccharide, and by conserved genes, that constitute good targets for strategies developed against pneumococcal infections. Proteins Wzd and Wze, the products of two of these conserved genes, were the focus of our work.
Wzd and Wze belong to the Bacterial tyrosine kinase family of proteins, whose members are involved in the regulation of the synthesis and export of bacterial capsular and extracellular polysaccharides which play essential roles in the initial stages of infection by pathogenic bacteria. Also, bacterial tyrosine kinases possess unique structural features with no equivalent in eukaryotic kinases. For these reasons, proteins that belong to this family constitute good novel antibacterial targets.
Bacterial tyrosine kinases are composed by a sensing transmembrane domain (in pneumo CPS this is Wzd) and by an intracellular catalytic domain (Wze). The intracellular catalytic domain has two important conserved motifs: a Walker A ATP binding motif and a C-terminal tryosine cluster. These two motifs were shown previously to be important for the regulation of CPS synthesis by Wze: ATP binding is necessary for the the prodcution of capsule and the phosporylation of the C-terminal tyrosines is importante in the attachment of the CPS to the cell wall. Wzd is necessary for the autophosphorylation of Wze. Based on these results, a model for the regulation of CPS synthesis by Wzd and Wze has been proposed (Figure 1).
In the present work we report a previously uncharacterized role of Wzd and Wze in the coordination of the CPS synthesis with pneumococcal cell division, by showing that these two proteins localize at the division septum and that this localization is required for the presence of CPS at the septum. We propose that proteins Wzd and Wze may act as spatial regulators of capsule metabolism, ensuring CPS is produced synchronously with the synthesis of peptidoglycan at the division septum.



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