Ammonia assimilation enzymes in a thermophilicBacillus sp. of marine origin

Abstract

The physiology of ammonia assimilation enzymes was examined in Bacillus sp. FE-1, a thermophilic marine bacterium. Glutamine synthetase (GS) and glutamate synthase (GOGAT) activities varied with the nitrogen source present in the medium, ranging as much as 10-fold for the former and 2.5-fold for the latter. Glutamate dehydrogenase (GDH) was detected but, under the growth conditions studied, levels were not affected by the nitrogen source. Anaerobic growth in the presence of nitrate yielded enzyme levels that were not significantly different from those measured under aerobic growth. Partially purified GS exhibited a temperature optimum between 65 ~ and 75~ The enzyme's Mn2+-dependent reverse transferase activity was stimulated by KzSO 4 and demonstrated some tolerance to NaC1. Hyperbolic kinetics were observed for ammonium, with an apparent KM of 1.0 raM. Members of the genus Bacillus exhibit an elaborate adaptive response to conditions of environmental stress. Nutrient deprivation, for example, will trig- ger a complex sequence of physiological and mor- phological changes resulting in endospore develop- ment. While research into the physiology and molecular biology of spore formation has focused on the mesophile Bacillus subtilis, comparatively little is known about the regulation of gene expres- sion in the thermophilic and psychrophilic represen- tatives of the genus. Furthermore, Bacillus strains isolated from the marine environment have not been examined in any detail. Although these species ac- count for only a small percentage of the bacteria in the ocean, they may provide further insight into the strategies utilized by marine bacteria enabling them to adapt to their surroundings. We have been studying strain FE-1, a thermo- philic Bacillus sp. of marine origin, that was isolated from sediments of the West Florida Escarpment cold seep (10). These seep communities resemble those associated with hydrothermal vents discovered along East Pacific Rise ridge crests. Escarpment sed- iment had characteristically high concentrations of