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Strategies for the study of mechanisms underlying pneumococcal intra-species interactions
Publication . Dias, Ana Sofia Veríssimo; Valente, Carina
Streptococcus pneumoniae is a major human pathogen that colonizes the nasopharynx, where multiple strains often co-exist. Co-colonization promotes intra-species interactions that shape bacterial fitness, persistence, and transmission. These dynamics are central to pneumococcal ecology and epidemiology, yet their underlying molecular mechanisms remain poorly understood. Previous work from our group identified two contrasting phenotypes: a positive, interaction of commensalism between strains 15A and NT1, and a negative, interaction of amensalism between strains 19F and NT2.
This thesis aimed to investigate these interactions using a non-targeted approach, based on differential fluorescence induction to capture condition-dependent gene regulation.
Despite extensive optimization, blunt-end ligation of genomic fragments into pDL278 proved inefficient and prevented reliable in-house library construction. A commercially synthesized promoter library was obtained for strain NT1, allowing non-targeted analysis of the positive interaction through differential fluorescence induction, while the negative interaction was explored using a targeted hypothesis-driven approach.
For the positive interaction, optimization of biofilm growth and development of suitable controls enabled FACS-based screening and enrichment of condition-responsive clones. Preliminary results showed increased promoter activity when NT1 was co-cultured with a capsule-deficient 15A mutant, implicating the capsule as a key determinant of transcriptional modulation during interactions.
For the negative interaction, sequential deletion of bacteriocin loci revealed that inhibition of NT2 by 19F depends on the cumulative activity of multiple bacteriocins. Competence-mediated fratricide was identified as an additional synergistic mechanism, while residual inhibition suggested contributions from other loci, such as Streptococcin A, or competence-regulated autolysins.
Overall, this work shows that pneumococcal intra-species interactions are multifactorial and context-dependent. Positive interactions reflect capsule-dependent transcriptional plasticity, whereas negative interactions rely on overlapping and redundant inhibitory mechanisms. Together, these findings highlight the dual strategies of adaptability and redundancy that sustain pneumococcal coexistence and competition in the nasopharynx, with important implications for colonization dynamics, serotype replacement, and vaccine design.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
Concurso de Projetos de I&D em Todos os Domínios Científicos - 2022 - PEX
Número da atribuição
2022.10980.PTDC