Physiological effects of long-term energy-source deprivation on the survival of a marine chemolithotrophic ammonium-oxidizing bacterium

Abstract

The response of the marine chemolithotrophic ammonium-oxidizing bacterium Nitroso-monas cryotolerans was examined during energy-source deprivation. The response to starvation differed from heterotrophic bacteria in almost every aspect examined. Levels of protein, RNA and DNA remained essentially unchanged during the 10 wk starvation period. The organism maintained an active electron transport system throughout the study. After an initial large increase, potential ammonium-oxidizing act~vity remained at high levels throughout starvation. The energy charge of N, cryotolerans was very low (0.68) at the onset and decreased with starvation until 5 wk when it stabilized at 0.50 and remained constant throughout the remainder of the study. ATP remained nearly constant for 2 wk then decreased until 4 wk when it stabilized at 0.85 fmol ml-' at 10"ells ml-' N. cryotolerans appears to be well adapted to energy-source deprivation. It is able to conserve energy by lowering its energy charge and repressing biosynthesis. It also maintained a state of readiness which allowed it to respond quickly to nutrient addition. These results indicate that this organism is well adapted to oligotrophic environments (i.e. the open ocean) where substrates are often limiting.