Fig. 2: ssnA encodes the extracellular nuclease of S. gordonii.
a Schematic diagram of the domain organisation of the protein encoded by the ssnA gene. Positions of predicted domains including a putative signal peptide (SP), an OB-fold, a nuclease domain and an LPxTG cell wall anchoring motif are marked with start and end amino acid residue numbers from the N-terminus. b Extracellular DNase activity was assessed using DNase Test agar. A clear halo around colonies of wild S. gordonii DL1 indicates DNase activity. No halo was visible in S. gordonii ΔssnA, whereas extracellular DNase activity was restored in S. gordonii ssnAComp. c The cell fraction and spent culture media were separated by centrifugation of planktonic cultures of wild type S. gordonii, the ΔssnA mutant and ssnAComp strains, and the nuclease activity of each fraction was determined using a fluorescence based quantitative assay. S. aureus FH7 was included as a control. Extracellular DNase activity of S. gordonii was associated primarily with the cells, whereas S. aureus DNase activity was higher in conditioned medium. Identical volumes of cellular and supernatant fractions were used in analysis. Data points are shown for 3 independent repeats, bars represent the mean and SD is indicated.
