Streptococcus pneumoniae fratricide-induced cell lysis does not require the type IV competence pilus

Streptococcus pneumoniae , a bacterium that becomes competent naturally, can undergo transformation and fratricide during which different genes, including antibiotic-resistant ones, can be transferred. A Type IV pilus (T4P) is involved in the DNA take up during transformation or fratricide-induced (fratricide = same species cell killing) gene transfer. Here, contrary to our expectations, we show that competence T4P is not required in fratricide-induced cell lysis. We have utilized pilus⁺ and pilus⁻ attackers, and a β-galactosidase ⁺ (β-gal ⁺ ) victim for our experiment. Transformation, gene transfer efficiency, and cell lysis measured by release of β-gal ⁺ were tested at different optical cell densities (OD) under competence-induced (+CSP) or non-competence (-CSP) conditions. We have optimized experiment conditions to observe cell lysis, which only occurred in the media that do not contain choline (inhibits cell lysis). As expected, we have observed transformation and gene transfer with the pilus ⁺ strain, but none of those two processes with the pilus ^- strain. In the case of β-gal release during fratricide, we have observed β-gal activity in both cases whenever the pilus ⁺ or pilus ^- strain was mixed with the β-gal ⁺ victim. Our data indicate that type IV competence pilus, while crucial for DNA take up during transformation fratricide, is not needed during cell lysis.