Different Metabolomic Responses to Carbon Starvation between Light and Dark Conditions in the Purple Photosynthetic Bacterium, <i>Rhodopseudomonas palustris</i>

Abstract

Purple photosynthetic bacteria utilize light energy for growth. We previously demonstrated that light energy contributed to prolonging the survival of multiple purple bacteria under carbon-starved conditions. In order to clarify the effects of illumination on metabolic states under carbon-starved, non-growing conditions, we herein compared the metabolic profiles of starved cells in the light and dark using the purple bacterium, Rhodopseudomonas palustris. The metabolic profiles of starved cells in the light were markedly different from those in the dark. After starvation for 5 d in the light, cells showed increases in the amount of ATP and the NAD+/NADH ratio. Decreases in the amounts of most metabolites related to glycolysis and the TCA cycle in energy-rich starved cells suggest the active utilization of these metabolites for the modification of cellular components. Starvation in the dark induced the consumption of cellular compounds such as amino acids, indicating that the degradation of these cellular components produced ATP in order to maintain viability under energy-poor conditions. The present results suggest that intracellular energy levels alter survival strategies under carbon-starved conditions through metabolism.

ATP is a major determinant of phototrophic bacterial longevity in growth arrest

“…We found that although light-incubated cells maintained high levels of intracellular ATP over a period of 25 d following growth arrest, ATP levels dropped to undetectable levels over the same period in dark-incubated cells. These results are in line with those obtained with the same strain of R. palustris (CGA009) by Kanno et al(20) In addition, these investigators measured the adenylate energy charge ([ATP] + 0.5 [ADP])/[ATP] + [ADP] + [AMP]) (21) of light and dark-incubated cells at day 5 post-growth arrest and found that whereas the energy charge of light-incubated cells matched that of growing cells, the energy charge of dark-incubated cells was dramatically lower. We note that intracellular ATP levels dropped in advance of losses of viability, suggesting that energy depletion caused cell death.…”

Effects of light / dark diel cycles on the photoorganoheterotrophic metabolism ofRhodopseudomonas palustrisfor differential electron allocation to PHAs and H2

“…As reported by Kanno et al. (55), the photosynthetic units are not disassembled in the dark, even under starvation. These are readily available, once the light conditions are restored, to produce ATP and NADH for the biosynthetic processes.…”

Enhancing the Light Coverage of Photosynthetic Bacteria to Augment Photosynthesis by Conjugated Polymer Nanoparticles

“…ATP is an essential energy source in the metabolic activities including photosynthesis of R. palustris, and the ATP synthesis is attributed to the increased generation of proton gradient . ATP production efficiency of R.…”

“…ATP is an essential energy source in the metabolic activities including photosynthesis of R. palustris, and the ATP synthesis is attributed to the increased generation of proton gradient. 43 ATP production efficiency of R. palustris was also studied to further prove the effect of R. palustris/CPNs-TAT on the photosynthesis of R. palustris. The ATP production of R. palustris in the presence of CPNs-TAT was measured by ATP kit.…”