Adenine Nucleotide Pools During Starvation of Beneckea natriegens

Abstract

The marine bacterium Beneckea natriegens was grown in batch culture on a glucose/ NH,+/salts medium; growth terminated due to either carbon or nitrogen depletion from the medium. Nitrogen-limited cultures converted part of the excess glucose into glycogen whereas the carbon-limited cultures formed little glycogen. Glycogen-rich cultures survived longer than glycogen-poor cultures during starvation. Little protein was utilized during starvation and RNA was degraded as the primary endogenous source of energy. Glycogen was consumed only when the RNA content had decreased to about a third of the growth value.The adenine nucleotide content of nitrogen-limited cultures increased at the start of the stationary phase but the energy charge remained at the growth value of 0.9 to 0.95. The maximum size of the adenine nucleotide pool depended on the concentration of glucose remaining in the medium at the start of the stationary phase but a limiting value of about 60 pmol ATP (g protein)-l was attained, compared with 12 to 14 pmol ATP (g protein)-l in exponentially growing cultures. During extended starvation of both glycogen-rich and glycogen-poor cultures, there was a large decrease in adenine nucleotide content, but the energy charge remained above 0-6 even when viability was very low. I N T R O D U C T I O NThere are many factors that can cause loss of viability of bacteria (Dawes, 1976). During long-term starvation, endogenous metabolites such as non-essential RNA, protein and reserve polymers (glycogen, poly-P-hydroxybutyrate, triacylglycerols and polyphosphate) act as energy sources permitting essential maintenance processes to occur, thereby preserving viability (Dawes & Senior, 1973). Under these circumstances loss of viability may be related to the inability to regenerate ATP due to depletion of endogenous metabolites and reserve polymers. This would be seen as a decrease in the adenine nucleotide content or as a decrease in the ATP : ADP and ATP : AMP ratios, which may be measured as a decrease in energy charge (Atkinson, 1968(Atkinson, , 1978Chapman & Atkinson, 1977;Knowles, 1977Knowles, ,1979.There have been few studies on the adenylate pools of starving bacteria. Chapman et uZ. (1 97 1) showed that, following nitrogen depletion from a glucose-containing growth medium, there was a gradual decrease in the intracellular energy charge of Escherichia cofi strain B from a growth value of about 0-8 to between 0.6 and 0-5 after 60 to 80 h, without loss of viability. The intracellular adenine nucleotide content also decreased during this period. After 60 to 80 h, a rapid decrease in energy charge occurred, coincident with a loss of viability. Montague & Dawes (1974) showed a similar relationship of decrease in energy charge and loss of viability during starvation of Peptococcus pre'votii, which does not form reserve polymers but utilizes RNA as the sole endogenous source of energy. 7 Present address: The College of the Resurrection, Mirfield, West Yorkshire WF14 OBN.

Oligotrophy

“…The major problem for the starving bacterium generally seems to be the provision of sufficient energy for maintenance of structural integrity, internal and membrane-associated macromolecules, proton gradients (Hueting et al, 1979), and energy charge (Nazly et al, 1980). Cells containing PS or PHB reserves are, in almost all instances examined, better able to survive periods of starvation than polymer-poor cells (Dawes and Senior, 1973;Dawes, 1976), principally through the mechanism of utilization of the reserves as a source of energy, which spares the degradation of more critical cell components such as RNA and protein.…”

Long term starvation of a marine bacterium,Alteromonas denitrificans, isolated from a Norwegian fjord

“…In Beneckea natriegens RNA was degraded before the proteins [32]. After an initial phase of active reorganization of the cell, some bacteria show a change in their protein pattern upon starvation [33].…”

Advances in Microbial Ecology

“…An energy-charge of about 0.95 was demonstrated with Beneckea natriegens when growing in nutrient-rich medium; it decreased slowly from about the 13th hour, but was still 0.6 at 50 hr when the total adenylate content was less than 10% of the maximum level and the viability was only 6% of the original culture (Nazly et al, 1980). Cells grown in carbon-limited chemostats maintain normal ATP pools and therefore have a high energy charge .…”

“…Beneckea natriegens, when grown with limited nitrogen, converts the excess glucose in the medium to glycogen, and glycogen-rich cultures survived longer than glycogen-poor cultures during starvation (Nazly et al, 1980). However, their experiments were only 50 hr.…”