Revisiting the genomes of the Staphylococcus aureus strains NCTC 8325 and RN4220.

Whole-genome sequence comparison of Staphylococcus aureus strain RN4220ΔmutS, a variant of strain RN4220 carrying an insertion in the mutS gene, and its parent strain S. aureus NCTC 8325 identified variations in the nucleic acid sequence between both strains. Some of these changes concerned proteins which are part of the ribosome (RpmF, RpsB), process ribosomal RNA (RimM), are involved in cell wall biosynthesis (EzrA, MurA), or possess chaperone functions (GroEL) and therefore might compromise the fitness of the affected strain. Resequencing of these genes in S. aureus NCTC 8325 revealed that the sequence variations represent errors in the original S. aureus NCTC 8325 genome sequence and do not constitute mutations in S. aureus RN4220 or RN4220ΔmutS. In correlation with these results, growth experiments showed that the fitness of S. aureus RN4220 is comparable to that of S. aureus NCTC 8325.