Halophilic bacteria

Abstract

The salt-fish industry of the United States suffers a large annual loss as a result of the salt fish developing a red coloration during the summer or when stored under warm moist conditions. Work undertaken by the U. S. Bureau of Fisheries has demonstrated that the red coloration is due to the growth of two microorganisms whose origin is the solar evaporated sea salt with which the fish are cured. The coloration may vary from a pale opaque pink to a deep transparent crimson due to the harmonious intergrowth of a spirochete producing a pale pink coloration and a bacterium producing a transparent red coloration. Likewise their separation into pure culture is difficult. These organisms exhibit very decided helio-, thermo-, and halophilic characteristics. The optimum concentration of salt for growth forms is saturation, growing luxuriantly on heavily salted fish, brine, sea salt, and saturated salt-fish agar. No growth appears on media containing less than 16 per cent. sea salt by weight. The shape, size, and motility of both forms is dependent upon the salt concentration of the medium, varying from the largest form found in saturated media (14 micra) to the spherical forms (2 micra) found in media of 18 per cent. concentration with all the intermediate forms between. The motility varies from the actively motile long forms, through a tumbling motion in the intermediates, to the non-motile spheres. The amount, character and coloration of the colonial growth does not seem to be affected by the changes in the concentration. Due to their extreme halophilic requirements, the staining of these organisms is very difficult. The optimum temperature for growth is 50° to 55° C. Both forms are strictly aerobic and produce neither gas nor acid in carbohydrates.