Publicação
New insights into the sociomicrobiology of Streptococcus pneumoniae : exploring biofilm formation
| Resumo: | During the last decade it has become more evident that Streptococcus pneumoniae (pneumococcus) holds a high genetic diversity throughout its population. Two important biological resources for achieving pneumococcalgenetic plasticity are competence/natural transformation and phage transduction. Both factors strongly contribute to genome modification and have a real impact in the capacity of survival and adaptation of this bacterium. Another important survival skill of the pneumococcus is its ability to form matrix‐enclosed biofilms. These microbial communities guarantee protection from environmental threats such as host immune defenses and antibiotics. Moreover, due to the fact that bacteria are believed to spend most of their lifetime in biofilms and that there is a higher physical proximity of bacteria within these structures, biofilms are probably the prefered stage for the occurrence of genetic exchange between pneumococci. This thesis contributes to a better understanding of the mechanisms that generate pneumococcal genetic diversity and the important bacterial ability to form biofilms. In the pursuit of this goal, two biological conditions were selected: a) prophage carriage and b) pherotype characterization, resulting in three independent studies: i) the study of the impact of prophage spontaneous activation on pneumococcal biofilm formation, ii) a molecular epidemiology study of the distribution of pherotypes and its contribution to pneumococcal genetic differentiation and iii) the study of the influence of pherotypes on pneumococcal biofilm growth and recombination efficiency. The study of the effect of prophage carriage and its spontaneously induced host lysis on pneumococcal biofilms reveal that, although limited phage induction results in the death of their bacterial hosts, the bacterial population as a whole benefits from prophage carriage and an enhancement in biofilm formation is observed. Moreover, this study shows a link between the external DNA (eDNA) that is released to the medium due to bacterial lysis and the growth of pneumococcal biofilms. The molecular epidemiology study performed showed that of the two dominants pherotypes (CSP1 and CSP2) the majority of the invasive isolates screened presented the CSP1 pherotype. Several associations with the pherotypes and other biological markers were observed indicating that pherotypes are not randomly distributed within the pneumococcal population. Associations with serotype, antimicrobial resistance and genetic lineage were unveiled; it was also detected that phage transduction may be indirectly arbitrated by pherotypes, implicating an uneven distribution of large genetic elements such as some genetic determinants of antibiotic resistance. The study also showed that strains that are phylogenetically closer have a higher likelihood of sharing the same pherotype. Severe limitations to inter‐pherotype communication may be leading towards an ongoing genetic drift, explaining the two genetically distinct subpopulations that were detected. Moving forward, we decided to explore the impact of the two major pherotypes on both the capacity to form biofilms and on recombination efficiency. Biofilms of strains presenting CSP1 had increased biofilm mass and were more densely packed. Also, the addition of synthetic cognate CSP amplifies the observed differences in biofilm growth between the pherotypes. The study also revealed that CSP1 strains transform more efficient both in the liquid medium and within the biofilm structure. Taken together this thesis work has shown that genetic exchanges between pneumococcal strains are occurring preferentially between strains sharing the same pherotypes and that the enhancement of biofilm formation detected both by prophage carriage and by CSP signaling have in common the positive impact of DNA release to the extracellular medium resulting from the lysis of a fraction of the bacteria inside the biofilm.A última década assistiu a um aumento das evidências reunidas sobre a elevada diversidade genética existente na população de Streptococcus pneumoniae. |
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| Autores principais: | Carrolo, Margarida, 1978- |
| Assunto: | Microbiologia Streptococcus pneumoniae Biofilmes Teses de doutoramento - 2011 |
| Ano: | 2011 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | During the last decade it has become more evident that Streptococcus pneumoniae (pneumococcus) holds a high genetic diversity throughout its population. Two important biological resources for achieving pneumococcalgenetic plasticity are competence/natural transformation and phage transduction. Both factors strongly contribute to genome modification and have a real impact in the capacity of survival and adaptation of this bacterium. Another important survival skill of the pneumococcus is its ability to form matrix‐enclosed biofilms. These microbial communities guarantee protection from environmental threats such as host immune defenses and antibiotics. Moreover, due to the fact that bacteria are believed to spend most of their lifetime in biofilms and that there is a higher physical proximity of bacteria within these structures, biofilms are probably the prefered stage for the occurrence of genetic exchange between pneumococci. This thesis contributes to a better understanding of the mechanisms that generate pneumococcal genetic diversity and the important bacterial ability to form biofilms. In the pursuit of this goal, two biological conditions were selected: a) prophage carriage and b) pherotype characterization, resulting in three independent studies: i) the study of the impact of prophage spontaneous activation on pneumococcal biofilm formation, ii) a molecular epidemiology study of the distribution of pherotypes and its contribution to pneumococcal genetic differentiation and iii) the study of the influence of pherotypes on pneumococcal biofilm growth and recombination efficiency. The study of the effect of prophage carriage and its spontaneously induced host lysis on pneumococcal biofilms reveal that, although limited phage induction results in the death of their bacterial hosts, the bacterial population as a whole benefits from prophage carriage and an enhancement in biofilm formation is observed. Moreover, this study shows a link between the external DNA (eDNA) that is released to the medium due to bacterial lysis and the growth of pneumococcal biofilms. The molecular epidemiology study performed showed that of the two dominants pherotypes (CSP1 and CSP2) the majority of the invasive isolates screened presented the CSP1 pherotype. Several associations with the pherotypes and other biological markers were observed indicating that pherotypes are not randomly distributed within the pneumococcal population. Associations with serotype, antimicrobial resistance and genetic lineage were unveiled; it was also detected that phage transduction may be indirectly arbitrated by pherotypes, implicating an uneven distribution of large genetic elements such as some genetic determinants of antibiotic resistance. The study also showed that strains that are phylogenetically closer have a higher likelihood of sharing the same pherotype. Severe limitations to inter‐pherotype communication may be leading towards an ongoing genetic drift, explaining the two genetically distinct subpopulations that were detected. Moving forward, we decided to explore the impact of the two major pherotypes on both the capacity to form biofilms and on recombination efficiency. Biofilms of strains presenting CSP1 had increased biofilm mass and were more densely packed. Also, the addition of synthetic cognate CSP amplifies the observed differences in biofilm growth between the pherotypes. The study also revealed that CSP1 strains transform more efficient both in the liquid medium and within the biofilm structure. Taken together this thesis work has shown that genetic exchanges between pneumococcal strains are occurring preferentially between strains sharing the same pherotypes and that the enhancement of biofilm formation detected both by prophage carriage and by CSP signaling have in common the positive impact of DNA release to the extracellular medium resulting from the lysis of a fraction of the bacteria inside the biofilm.A última década assistiu a um aumento das evidências reunidas sobre a elevada diversidade genética existente na população de Streptococcus pneumoniae. |
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