Parallel Evolution in Streptococcus pneumoniae Biofilms.

Area of Science:

• Microbiology
• Genetics
• Pathogenesis

Background:

• Streptococcus pneumoniae is a common cause of human diseases.
• Nasopharyngeal carriage is linked to pneumococcal biofilm formation.
• Biofilm environments promote genetic diversification, leading to phenotypes like small colony variants (SCVs).

Purpose of the Study:

• To investigate the genetic basis and phenotypic characteristics of biofilm-derived SCVs in Streptococcus pneumoniae.
• To understand the role of SCV formation in pneumococcal diversification during biofilm development.

Main Methods:

• Metabolic characterization of biofilm-derived SCVs.
• Whole-genome sequencing of 12 independent SCV isolates.
• Phenotypic profiling including growth rates and capsule expression analysis.

Main Results:

• SCVs exhibited reduced growth rates, decreased capsule expression, altered metabolism, and increased biofilm formation compared to the ancestral strain.
• All 12 sequenced SCVs possessed mutations in the DNA-directed RNA polymerase delta subunit (rpoE) gene.
• Mutations included deletions, frameshifts, and nonsense substitutions leading to truncated RpoE.

Conclusions:

• Mutations in the rpoE gene are directly linked to SCV formation and enhanced biofilm development in Streptococcus pneumoniae.
• This finding has significant implications for understanding pneumococcal colonization, carriage, and persistence.
• The recurrent mutation of rpoE demonstrates parallel evolution in pneumococcal biofilm development.