Energy Metabolism of Rickettsia typhi : Pools of Adenine Nucleotides and Energy Charge in the Presence and Absence of Glutamate

Abstract

The obligate intracellular bacterium Rickettsia typhi was examined for its ability to generate and maintain an adenylate energy charge in an extracellular environment. Freshly purified organisms were incubated, at 340C and pH 7.4, with or without glutamate and various other metabolites, and the levels of ATP, ADP, and AMP were determined. Of the metabolites tested, glutamate and glutamine were the most effective for the generation of ATP. In the presence of glutamate, there was a rapid increase in the level of ATP, followed by a moderate decrease during 150 min of incubation. The energy charge increased from a level of 0.2 to 0.5 to about 0.7 to 0.75, and then slowly declined to about 0.45 to 0.6. In the absence of glutamate, after an occasional initial surge in ATP level as the temperature was changed from 4 to 340C, there was a sharp decline in both ATP and energy charge (to 0.1 and sometimes to 0.01). The rickettsiae maintained their ability to regenerate their energy charge upon the addition of glutamate for about 30 min, but this ability declined with further incubation. In contrast to Escherichia coli, the decline in ATP in R. typhi was accompanied by a sharp increase in the level of AMP and the total adenylate pool. No adenine or adenosine was recovered from rickettsiae incubated with labeled AMP, ADP, or ATP. From these experiments and the demonstration reported elsewhere that rickettsiae transport the adenine nucleotides, it can be concluded that the adenylate energy charge in R. typhi is governed by the salvage of the adenine nucleotides rather than their unphosphorylated precursors. Thus, R. typhi undergoes greater shifts in energy charge than other bacteria, a phenomenon which may account for their instability in an extracellular environment. Under optimal conditions the adenylate energy charge of R. typhi approaches levels that border on those generally regarded as adequate for growth.

Transmembrane electrical potential in Rickettsia prowazekii and its relationship to lysine transport

“…These processes have been shown (5-7, 9, 13, 24, 28) in other systems to be dependent on both an intact cytoplasmic membrane and a transmembrane proton electrochemical gradient, the protonmotive force (PMF). The fact that both ATP synthesis and lysine transport are inhibited by protonophores and by high concentrations of the lipophilic cation triphenylmethylphosphonium strongly supports the hypothesis that rickettsiae can generate and maintain a PMF (2,18,27, 33). Although the integrity of the rickettsial cytoplasmic membrane has been questioned, it appears that this component of the rickettsial cell does provide a barrier to certain compounds, is not t Present address:…”

“…The rickettsiae may not require host-cell-degrowazekii metab-rived high energy compounds to multiply. It has dialysis was per-been established (2,26,27) that these bacteria upper chamber of possess the metabolic capability through oxidaf energy-depleted tive phosphorylation to generate their own ATP, nl). [3H]TPP was the main currency of energy in biological syss accomplished by tems.…”

“…R. prowazekii, Madrid E strain, was cultivated and purified as previously described (31) with the addition of a filtration step through AP-25 filters (Millipore Corp., Bedford, Mass.) (27). When necessary, the rickettsiae were further purified by equilibrium density gradient centrifugation through a linear gradient of 25 to 45% Renografin-76 (E. R. Squibb & Sons, Princeton, N.J.) in a manner similar to that described by Weiss et al (23).…”

“…However, these studies have yielded much information concerning the metabolic capabilities of the rickettsiae (21,22). Pertinent to the subject of this paper are the observations that rickettsiae synthesize ATP upon the oxidation of glutamate via the tricarboxylic acid cycle by a mechanism sensitive to uncouplers (oxidative phosphorylation) (2,26,27,33) and actively transport at least one amino acid, lysine (18). These processes have been shown (5-7, 9, 13, 24, 28) in other systems to be dependent on both an intact cytoplasmic membrane and a transmembrane proton electrochemical gradient, the protonmotive force (PMF).…”

Stability of the Adenosine 5′-Triphosphate Pool in Coxiella burnetii : Influence of pH and Substrate

“…Effect of pH and substrate oxidation on the ATP pool. The ability of C. burnetii to couple glutamate oxidation to ATP synthesis was examined and compared with energy coupling as described for typhus rickettsiae (23). The effect of pH on endogenous ATP synthesis from glutamate oxidation by whole cells of C. burnetii is depicted in Fig.…”