An antibiotic-producing pseudomonad was isolated from a seawater sample from a La Jolla, Calif., tidepool. The pseudomonad produces two novel antibacterial compounds, 2-n-pentyl-4-quinolinol and 2-n-heptyl-4-quinolinol. It also synthesizes indole-3-carboxaldehyde, 6-bromoindole-3-carboxaldehyde, and the known antibiotic p-hydroxybenzaldehyde. Each of these compounds was identified by analysis of spectral data, and the structures were confinred by synthesis or comparison with authentic samples.Although the production of antibiotics by marine bacteria is well documented (3, 4), there have been few chemical studies of this phenomenon. In a pioneering chemical study, Burkholder et al. (5) isolated a highly brominated antibiotic I (Fig. 1) from an organism they designated Pseudomonas bromoutilis. We have subsequently isolated the same antibiotic, together with tetrabromopyrrole (II) and hexabromo-2,2'-bipyrrole (Ill) (Fig. 1) from an autotoxic marine bacterium of the genus Chromobacterium (1). We could demonstrate that antibiotics I and II were responsible for autotoxicity. In this study we have elucidated the structures of two novel antibiotics and three other interesting metabolites from a marine pseudomonad.
MATERIALS AND METHODSIsolation, description, and culturing of the bacteria. The marine pseudomonad (designated 102-3) was isolated from a seawater sample taken from a mid-intertidal pool at La Jolla, Calif., on 4 March 1974. The bacterium showed antibiotic activity on the original agar plate spread with the water sample, as demonstrated by the formation of zones of inhibition around individual colonies. Zone-producing colonies were isolated, dilution streaked, and maintained in pure culture. 102-3 is a short (< 1 ,um), gram-negative, motile rod with no apparent storage granules. Optimum growth occurs in a medium that is 80 to 100% the sodium chloride concentration found in seawater. Potassium chloride will not replace sodium chloride as a required salt. This bacterium will not grow on a minimal medium (i.e., glycerol as the only carbon source) and grows only at temperatures between 9 and 24°C.The culture medium consisted of peptone (5 g/liter), yeast extract (1 g/liter), and agar (10 g/liter) in filtered seawater. Marine strains used as test organisms were Vibrio anguillarum M5900, obtained from W. Fenical of Scripps Institution of Oceanography, and Vibrio harveyi, obtained from K. Nealson, also of Scripps Institution of Oceanography. These were grown on the same medium as was 102-3. Staphylococcus aureus ATCC 6538P, Escherichia coli ATCC 11775, and Candida albicans ATCC 10231, obtained from Abbott Laboratories, were cultured on tryptic soy agar. Antibiotic activity was assayed using the agar diffusion method.Procedures for the indole, methyl red, VogesProskauer, nitrate reduction, sucrose, mannitol, catalase, and oxidase tests were those listed by Collins (6).Large-scale culture and extraction procedures. Large-scale cultures of 102-3 were grown on trays (60 by 30 by 2 cm) of nutrient agar (see above). After ...
