Nucleotide pools in growing Chromatium strain D

Metabolomic profiling of the purple sulfur bacterium Allochromatium vinosum during growth on different reduced sulfur compounds and malate

Environmental fluctuations require rapid adjustment of the physiology of bacteria. Anoxygenic phototrophic purple sulfur bacteria, like Allochromatium vinosum, thrive in environments that are characterized by steep gradients of important nutrients for these organisms, i.e., reduced sulfur compounds, light, oxygen and carbon sources. Changing conditions necessitate changes on every level of the underlying cellular and molecular network. Thus far, two global analyses of A. vinosum responses to changes of nutritional conditions have been performed and these focused on gene expression and protein levels. Here, we provide a study on metabolite composition and relate it with transcriptional and proteomic profiling data to provide a more comprehensive insight on the systems level adjustment to available nutrients. We identified 131 individual metabolites and compared availability and concentration under four different growth conditions (sulfide, thiosulfate, elemental sulfur, and malate) and on sulfide for a ΔdsrJ mutant strain. During growth on malate, cysteine was identified to be the least abundant amino acid. Concentrations of the metabolite classes "amino acids" and "organic acids" (i.e., pyruvate and its derivatives) were higher on malate than on reduced sulfur compounds by at least 20 and 50 %, respectively. Similar observations were made for metabolites assigned to anabolism of glucose. Growth on sulfur compounds led to enhanced concentrations of sulfur containing metabolites, while other cell constituents remained unaffected or decreased. Incapability of sulfur globule oxidation of the mutant strain was reflected by a low energy level of the cell and consequently reduced levels of amino acids (40 %) and sugars (65 %).

Interaction of inactivated and active ribulose 1,5-bisphosphate carboxylase/oxygenase of Rhodobacter sphaeroides with nucleotides and the chaperonin 60 (GroEL) protein

Purified inactivated form I ribulose 1,5-bisphosphate carboxylase/oxygenase (form I RubisCO) of Rhodobacter sphaeroides was activated by ATP and, to some extent, by other adenylates and nucleotides. Reactivation in the presence of ATP occurred by a time-dependent and concentration-dependent process which appeared to be irreversible. The carbamylated form of inactivated form I RubisCO was less susceptible to ATP-mediated reactivation than the uncarbamylated inactivated enzyme. In some cases, ATP analogs could mimic the reactivation process; one analog, adenylyl(beta, gamma-methylene)-diphosphonate, was found to partially block ATP-mediated reactivation but could not block reactivation induced by Mg(II). Concomitant with the recovery of enzymatic activity, the migration of the inactivated form I RubisCO on nondenaturing and sodium dodecyl sulfate gels changed from a pattern that was characteristic of inactivated enzyme to a pattern that was identical to that of the active protein. It was further found that discrete proportions of active enzyme and the chaperonin 60 protein of R. sphaeroides aggregated in the presence of ATP. The form I RubisCO is thus proposed to contain a specific ATP-binding site that may contribute to both the regulation of activity and the assembly of active enzyme.

Variation in guanosine 5' ,3'-tetraphosphate levels in Chromatium

Chromatium produces guanosine 5' ,3'-tetraphosphate, but there appears to be no correlation between guanosine 5' ,3'-tetraphosphate concentration and the inability of the organism to grow in certain light-dark regimes.

Adenine nucleotide levels in Neurospora, as influenced by conditions of growth and by metabolic inhibitors

By a combination of luciferase and fluorescence methods adenine nucleotide pools in Neurospora crassa have been examined under various conditions of growth and metabolic inhibition. During sustained exponential growth (25 C, shaking liquid cultures), the intracellular adenosine 5'-triphosphate (ATP) concentration, [ATP](i), rises slowly from the conidial level near 1 mM (1 mmol/kg of cell water) to a maximum of 2.0 to 2.5 mM at 14 h, after which it slowly declines. The adenosine 5'-diphosphate and adenosine 5'-monophosphate (AMP) curves show two peaks, at 8 and 20 h, with a minimum at 16 h. The "energy charge" function varies around a mean of 0.72 throughout the period of exponential growth. Transferral of growing cells to buffer lacking a nitrogen source stabilizes the [ATP](i) near 2.5 mM, apparently independent of the cell age, and most studies of metabolic inhibitors were carried out on cells grown 14 to 16 h and then shifted to N-free buffer. Under these conditions sudden respiratory blockade (cyanide) produces exponential decay of ATP with a time constant of about 5.7 s (half-time of 3.9 s), and at a rate which implies a minimal ATP turnover of 0.44 mM/min. This figure is about one-third the rate (1.17 mM/min) which would be calculated from steady-state respiration, a discrepancy which may partly be accounted for by transphosphorylation from appreciable amounts of non-adenine nucleoside di- and triphosphates present in Neurospora. For all three adenine nucleotides, the transients associated with sudden respiratory blockade include overshoots or undershoots of several minutes duration, which are consistent with feedback regulation of glycolysis by the AMP/ATP ratio.

Nucleotide pools and adenylate energy charge in balanced and unbalanced growth of Chromatium

Adenine nucleotide pools and their energy charge were measured during balanced and unbalanced growth of photoheterotrophic Chromatium cultures. The methods used involved rapid sampling, accurate to within 1 s, from isotopically labeled cultures followed by chromatographic separation of individual nucleotides. During balanced growth, both energy charge and adenosine triphosphate (ATP) concentrations, whether expressed as a function of cell protein or intracellular water, were slightly higher in limiting light intensities than in cultures growing at their maximal rate in bright light. The ATP found corresponded to 4.67 +/- 0.08 nmol/mg of protein or 1.34 +/- 0.57 mM for low-light cells and to 4.41 +/- 0.58 mmol/mg of protein or 0.85 +/- 0.12 mM for high-light cells. Corresponding energy charges were 0.85 +/- 0.02 and 0.81 +/- 0.02. Illumination shifts caused differential synthesis of photosynthetic pigments lasting 2 to 3 h without corresponding perturbation of adenine nucleotide levels. Cultures in intermittent illumination were severely affected by some cycle durations; they had abnormal morphology and very high bacteriochlorophyll-to-protein ratios. In such cultures, energy charge and nucleotide concentrations were within normal limits and relaxed to the dark steady state during the dark periods. Arsenate at AsO(4) (3-) to PO(4) (3-) ratios of 10:1 in the medium retarded growth, but no abnormality of charge or quantity of phosphate-containing nucleotides was found. These experiments therefore suggest that, within experimental error, neither the size nor the charge of the adenylate pools governs growth rate in Chromatium. Moreover, these parameters do not appear to be concerned in regulating the synthesis of photosynthetic apparatus in this organism.