Newantibiotics, plusbacins At~A4and Bt~B4, were isolated from the culture broth ofa strain of Pseudomonas sp. These antibiotics were isolated as a complexby columnchromatographies on Diaion HP-20 and silica gel, and then separated by HPLC. They are amphoteric in nature. The hydrochlorides are obtained as colorless powders, soluble in methanol and alkaline water. From their physico-chemical properties, these antibiotics are presumed to be acyloctapeptides containing a lactone linkage, and their differences occur in amino acid and fatty acid residues. The antibiotics are active against Gram-positive bacteria in vitro and in vivo. 817 In the course of our screening work for newantibiotics from bacterial strains, a strain numbered PB-6250 related to the genus Pseudomonas was found to produce an antibiotic principle, which showed inhibitory activity against methicillin-resistant Staphylococcus aureus and proved to be a cell wall synthesis-inhibitor. It was isolated as a complex of peptide antibiotics, which was then separated by HPLC into eight components. They were shown to be new antibiotics and named plusbacins A1~A4 and Bj~B4. Their structures will be presented in the succeeding paper1}.In this paper, the taxonomy of the producing strain, the production and isolation of the antibiotics as well as the physico-chemical and biological properties are presented.
TaxonomyThe producing organism numbered PB-6250 was isolated from a soil sample collected in Okinawa-honto, Okinawa Prefecture, Japan. The organism is an aerobic Gram-negative, non-sporulating rod (0.5~0.7 x 2.0~5.0 /mi) with rounded ends. It is weakly motile by one or several polar flagella. It exhibits good growth at 28°C and on nutrient agar it forms circular, convex, opaque, entire, glistening and wet colonies with brownish cream color. Soluble, brown pigment is diffused around colonies. Poly-/?-hydroxybutyrate is not accumulated as an intracellular carbon reserve. Other physiological characteristics are shownin Table 1.Acid formation was observed from D-glucose, D-fructose, maltose and trehalose, but not from D,L-arabinose, D-xylose, D-mannitol, lactose and sucrose. No gas formation was observed from the above carbohydrates.From comparison of these characteristics with those of bacteria registered in the Volume1 of Bergey's Manual of Systematic Bacteriology2), the organism should be ascribed to the genus Pseudomonas. According to further comparison with the registered species of the genus, the organism is most related to Pseudomonas paucimobilis, especially in the feeble motility, but differed in the inability of starch hydrolysis and mole% G+C ofDNA.
