A novel antibiotic naphthalecin was purified and isolated from the cells of an anaerobic bacterium isolated from a soil sample. This antibiotic contained a naphthalene moiety, so named as naphthalecin, and showed antibacterial activity against gram positive species. The producing strain, an obligate anaerobe, was identified as a new species of the genus Sporotalea. Identification of the bacterium, cultivation, purification, structure determination, and antibacterial activity are shown.Keywords antibacterial antibiotic, strictly anaerobic bacteria, naphthalene, naphthalecin, Sporotalea colonica
IntroductionDuring the screening of bacterial isolates from soil samples, an obligate anaerobic bacterium growing in a colony of an aerobic bacterium and a coculture of both strains with an antibacterially active mycelial form were found. After isolation of monocultures of both strains, we found that the anaerobe was the source of the antibiotic activity. As the reports on antibiotics produced by strictly anaerobic bacteria are few [1, 2], we tried to isolate the antibiotic from this anaerobic bacterium. The attempt resulted in the discovery of naphthalecin.
Results
Taxonomic StudyStrain SYB was a strictly anaerobic Gram-positive bacterium. Microscopic observation showed long, straight rods occurring singly or in pairs. As shown in Fig. 1, cells measured 2.0ϳ15.0 m m in length and 0.5ϳ0.8 m m in diameter and were motile with peritrichous flagella. In older cultures, cells formed refractile terminal endospores which were heat resistant (80°C, 10 minutes). Growth on BP agar was poor; a 14-day culture yielded small, circular, yellow colonies about 2ϳ3 mm in diameter. The temperature and pH ranges for growth were 15ϳ35°C (optimal 25ϳ30°C), and 6.0ϳ9.0 (optimal 7.0ϳ8.0), respectively.The 16S rRNA gene sequence of strain SYB determined in this study was almost complete, comprising 1,419 nt. The sequence showed that strain SYB was most closely affiliated with a strain of the genus Sporotalea [3,4]. A phylogenetic tree based on the neighbour-joining algorithm Naphthalecin, a Novel Antibiotic Produced by the Anaerobic Bacterium, Sporotalea colonica sp. nov.