Fratricide is essential for efficient gene transfer between pneumococci in biofilms

Area of Science:

• Microbiology
• Genetics
• Bacterial Physiology

Background:

• Streptococcus pneumoniae and other streptococci naturally undergo genetic transformation.
• These bacteria inhabit multispecies biofilms in the human oral cavity and nasopharynx.
• Gene exchange, including virulence and antibiotic resistance genes, occurs between streptococci in these environments.

Purpose of the Study:

• To investigate the role of the competence-specific murein hydrolase CbpD in mediating gene transfer within laboratory-grown biofilms.
• To determine if the fratricide mechanism enhances natural genetic transformation in a biofilm context.

Main Methods:

• Culturing Streptococcus pneumoniae in laboratory biofilms.
• Assessing gene transfer rates under different conditions.
• Analyzing the contribution of specific murein hydrolases (CbpD, LytC, LytA) to gene exchange.

Main Results:

• The fratricide mechanism, driven by CbpD, significantly increases intrabiofilm gene exchange.
• Competent S. pneumoniae cells acquire genetic markers more efficiently from neighboring cells than from the medium.
• Efficient cell lysis for DNA release requires CbpD acting with LytC, but not LytA.

Conclusions:

• The fratricide mechanism is vital for efficient homologous donor DNA acquisition in Streptococcus pneumoniae biofilms.
• CbpD-mediated lysis, in conjunction with LytC, plays a key role in natural genetic transformation within biofilms.
• LytA is not essential for fratricide-mediated gene exchange in this environment.