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Deletion analysis of Streptococcus pneumoniae late competence genes distinguishes virulence determinants that are dependent or independent of competence induction.

ABSTRACT: The competence regulon of Streptococcus pneumoniae (pneumococcus) is crucial for genetic transformation. During competence development, the alternative sigma factor ComX is activated, which in turn, initiates transcription of 80 'late' competence genes. Interestingly, only 16 late genes are essential for genetic transformation. We hypothesized that these late genes that are dispensable for competence are beneficial to pneumococcal fitness during infection. These late genes were systematically deleted, and the resulting mutants were examined for their fitness during mouse models of bacteremia and acute pneumonia. Among these, 14 late genes were important for fitness in mice. Significantly, deletion of some late genes attenuated pneumococcal fitness to the same level in both wild-type and ComX-null genetic backgrounds, suggesting that the constitutive baseline expression of these genes was important for bacterial fitness. In contrast, some mutants were attenuated only in the wild-type genetic background but not in the ComX-null background, suggesting that specific expression of these genes during competence state contributed to pneumococcal fitness. Increased virulence during competence state was partially caused by the induction of allolytic enzymes that enhanced pneumolysin release. These results distinguish the role of basal expression versus competence induction in virulence functions encoded by ComX-regulated late competence genes.

SUBMITTER: Zhu L

PROVIDER: S-EPMC4536566 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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Deletion analysis of Streptococcus pneumoniae late competence genes distinguishes virulence determinants that are dependent or independent of competence induction.

Zhu Luchang L Lin Jingjun J Kuang Zhizhou Z Vidal Jorge E JE Lau Gee W GW

Molecular microbiology 20150424 1

The competence regulon of Streptococcus pneumoniae (pneumococcus) is crucial for genetic transformation. During competence development, the alternative sigma factor ComX is activated, which in turn, initiates transcription of 80 'late' competence genes. Interestingly, only 16 late genes are essential for genetic transformation. We hypothesized that these late genes that are dispensable for competence are beneficial to pneumococcal fitness during infection. These late genes were systematically de ...[more]

PMID: 25846124

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Project description:Streptococcus pneumoniae is the major cause of bacterial pneumonia, and it is also responsible for otitis media and meningitis in children. Apart from the capsule, the virulence factors of this pathogen are not completely understood. Recent technical advances in the field of bacterial pathogenesis (in vivo expression technology and signature-tagged mutagenesis [STM]) have allowed a large-scale identification of virulence genes. We have adapted to S. pneumoniae the STM technique, originally used for the discovery of Salmonella genes involved in pathogenicity. A library of pneumococcal chromosomal fragments (400 to 600 bp) was constructed in a suicide plasmid vector carrying unique DNA sequence tags and a chloramphenicol resistance marker. The recent clinical isolate G54 was transformed with this library. Chloramphenicol-resistant mutants were obtained by homologous recombination, resulting in genes inactivated by insertion of the suicide vector carrying a unique tag. In a mouse pneumonia model, 1.250 candidate clones were screened; 200 of these were not recovered from the lungs were therefore considered virulence-attenuated mutants. The regions flanking the chloramphenicol gene of the attenuated mutants were amplified by inverse PCR and sequenced. The sequence analysis showed that the 200 mutants had insertions in 126 different genes that could be grouped in six classes: (i) known pneumococcal virulence genes; (ii) genes involved in metabolic pathways; (iii) genes encoding proteases; (iv) genes coding for ATP binding cassette transporters; (v) genes encoding proteins involved in DNA recombination/repair; and (vi) DNA sequences that showed similarity to hypothetical genes with unknown function. To evaluate the virulence attenuation for each mutant, all 126 clones were individually analyzed in a mouse septicemia model. Not all mutants selected in the pneumonia model were confirmed in septicemia, thus indicating the existence of virulence factors specific for pneumonia.

Dataset Information

Deletion analysis of Streptococcus pneumoniae late competence genes distinguishes virulence determinants that are dependent or independent of competence induction.

Publications

Deletion analysis of Streptococcus pneumoniae late competence genes distinguishes virulence determinants that are dependent or independent of competence induction.

Similar Datasets

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