Isolation of antibiotic-producing Pseudomonas species with low-temperature cultivation of temperate soil

We performed low-temperature cultivation of soil samples in Tokyo, Japan, and isolated 30 bacterial strains that formed colonies at 4°C. All the culture supernatants of these bacteria exhibited antibacterial activity against Escherichia coli. The 16S rDNA sequences of 29 strains showed similarity to that of the Pseudomonas genus, whereas the 16S rDNA sequence of one strain showed similarity to that of the Janthinobacterium genus. We classified the 29 strains into 10 groups according to the 16S rDNA sequence similarities, and performed two phylogenetic analyses using the 16S rDNA and rpoD gene sequences. Four groups formed a unique branch within Pseudomonas species in both phylogenetic analyses. Four other groups were closely related to the Pseudomonas species, but the most closely related species differed between the two phylogenic tree analyses. These results suggest that low-temperature cultivation of temperate soil is effective for isolating new bacterial sources for producing antibiotics.