Table 3.

Impact of LytF on the efficiency of gene transfer from donor to recipient cells during co-cultivation

DNA recipient strain	DNA source	Transformation efficiency during cocultivation (%)d	Transformation efficiency with genomic DNA (%)d
SGH25a	AH2	0.1 ± 0.019
SGH43a	AH2	0.001 ± 0.0002
SGH25b	AH2 DNA		0.87 ± 0.32
SGH43b	AH2 DNA		0.66 ± 0.16
SGH37c	SGH25	0.16 ± 0.046
SGH37c	SGH141	0.08 ± 0.016
SGH37c	SGH142	0.006 ± 0.001

^aThe S. gordonii Challis strains SGH25 (ΔcomA Str^r) and SGH43 (ΔcomA ΔlytF Str^r) were induced to competence with Challis CSP and cocultivated with the noncompetent strain AH2 (ΔcomA Rif^r). AH2, which is derived from S. gordonii strain NCTC 7865 does not respond to Challis CSP.

^bTransformation of the SGH23 and SGH43 strains with purified genomic DNA from the AH2 strain. Saturating amounts of DNA were used.

^cTo determine if competent target cells are immune against LytF, the Challis attacker strain SGH37 (ΔcomA Rif^r) was cocultivated with the Challis target strains SGH25 (ΔcomA Str^r), SGH141 (ΔcomA ΔcelB Str^r), and SGH142 (ΔcomA ΔcomD Str^r) in the presence of CSP. As it lacks the DNA permease CelB, the SGH141 target strain is not able to take up DNA during competence. The SGH142 target strain contains a disrupted comD gene and will therefore remain noncompetent even in the presence of CSP.

^dTransformation efficiency was estimated by dividing the number (CFU) of doubly resistant transformants by the total number (CFU) of competent recipient cells and multiplying by 100. Means and standard errors were calculated from three independent experiments.