This study analyzed DNA base composition (% GC content) in 29 Micrococcus strains to evaluate their taxonomic classification. The researchers used two complementary methods: melting temperature (Tm) analysis and ultraviolet absorption ratios. Results divided the strains into three groups: 17 strains whose GC content (65-75%) agreed with their Micrococcus classification; three strains with anomalously low GC values (35-41%) requiring reclassification, including Micrococcus cerolyticus and M. cryophilus; and five strains forming a distinct cluster around 50% GC, intermediate between Staphylococcus (low GC) and Micrococcus (high GC) genera. The five intermediate strains—including two M. roseus, two M. eucinetus, and one M. aquivivus—were predominantly marine organisms. The authors recommend transferring these five strains to the genus Planococcus based on their atypical GC content and other characteristics. The study confirms that GC content is a valuable taxonomic tool for Gram-positive cocci classification and supports the recognition of M. luteus and M. roseus as the primary Micrococcus species.

Key findings

• DNA GC content ranges from 65-75% in true Micrococcus species; strains outside this range should be reclassified
• Five marine and marine-related strains clustered tightly around 50% GC, intermediate between Staphylococcus and Micrococcus, and are recommended for transfer to genus Planococcus
• Micrococcus cerolyticus and M. cryophilus have anomalously low GC content (35-41%) consistent with Staphylococcus, indicating misclassification
• Two complementary methods (Tm and E260:E280 ratio) provided consistent results with differences of only 1-3% GC, validating both approaches
• DNA base composition is a reliable taxonomic character for Gram-positive cocci classification