Growth factor requirements of halophilic bacteria.

Despite the wide interest in halophilic bacteria for practical and scientific reasons, very little has been done on their organic nutritional requirements, although their inorganic requirements have received considerable attention (Robinson, 1950; Schoop, 1935). Various complex media utilizing fish infusions (Gibbons, 1936; Harrison and Kennedy, 1922; Lochhead, 1934), beef and yeast extracts or milk (Lochhead, 1934), and related substances (Robinson, 1950; Schoop, 1935) have been used for purposes of isolation and description, but few attempts have been made to culture these organisms on a chemically defined medium. Petter (1931) grew certain rod-forming red halophilic organisms in a synthetic medium with asparagine or glycine as a source of nitrogen, energy, and carbon but could not grow another group of these organisms unless peptone was used. Weber (1949) listed the constituents of a synthetic medium used to culture red halophiles, stating, however, that the addition of 0.1 per cent gelatin hydrolysate promoted heavy growth. The essential features of this medium were a high magnesium content, arginine, nitrate, citrate (as metal carrier), and an energy source such as succinate and glutamate. No vitamins or purines and pyrimidines were required. Using a similar medium Browne and Gibbons (1951) confirmed the requirements of a red halophile, Pseudom.onas salinaria, for unusually large amounts of magnesium as well as the absence of a requirement for vitamins. Pseudomonas nigrifaciens, an organism requiring from 1.5 to 3.0 per cent NaCl for optimal growth, has been reported to grow on a simple medium containing salts, glycerol, any one of a number of amino acids, and no vitamins (Katznelson and White, 1950). As part of a project on osmophilic organisms in general, an investigation was undertaken in this laboratory to determine the growth factor requirements of halophilic bacteria as the first step in developing a completely synthetic medium for them. Organisms ranging in NaCl requirement from 4 to 25 per cent, including nonchromogenic and chromogenic (red) forms were used and are listed in table 1, along with pertinent characteristics.