Growth Properties of Rhodospirillum rubrum Mutants and Fermentation of Pyruvate in Anaerobic, Dark Conditions

Abstract

Mutant C and G1 were obtained earlier from Rhodospirillum rubrum S 1 during growth in the dark under strict anaerobic conditions in medium containing sodium pyruvate. Mutant C and mutant G1 grew in the dark with generation times of 5.8 h and 4.6 h, respectively. Mutant C cells grew equally well when switched between anaerobic (dark or light) or aerobic, dark conditions. Mutant G1 cells grew only in the dark (anaerobic or aerobic conditions), but a fraction of cells in anaerobic, dark cultures grew when placed in light. This number increased about 3,000-fold when G1 cells were incubated aerobically in the dark. During anaerobic, dark growth, C and G1 organisms incorporated similar amounts of [2- 14 C ]sodium pyruvate. About 34% of the incorporated radioactivity was found in lipid fractions from C cells that developed chromatophores during dark growth. Similar results were obtained using G1 cells, which formed only trace amounts of photosynthetic structures. Both mutants fermented sodium pyruvate and produced acetate, formate, carbon dioxide, and hydrogen gas. Molar growth yield coefficients indicated that the cells obtained about 1 mol of adenosine triphosphate per mol of sodium pyruvate fermented. Results suggested that pyruvate fermentation during dark growth occurred via a pyruvate formate-lyase or the pyruvate ferredoxin-oxidoreductase pathway, or both.

Viability and Endogenous Substrates Used During Starvation Survival of Rhodospirillum rubrum

“…The only energy-yielding mechanism available to cells under such conditions is fermentation of intracellular reserve materials. Although R. rubrum is capable of fermentative ATP generation (13,29,30), the amount of ATP available for energy demands is minimal compared with that from photophosphorylation. The viability of phototrophically grown cells starved in the dark was extended by aerobic incubation, presumably because more energy became available to cells through oxidative phosphorylation.…”

Biochemical genetics revisited: the use of mutants to study carbon and nitrogen metabolism in the photosynthetic bacteria

“…sphaeroides in being able to carry out classical fermentative metabolism (although see [100]) by a mechanism involving pyruvate:formate lyase, which is inhibited by sodium hypophosphite [113]. Acetate, formate, H 2 and CO 2 appear to be the main fermentation products [114], although propionate, butyrate and succinate have also been detected [100,115]. There appears to be some interstrain variation, since strains S1 and Ha failed to produce acetate, and strain Ha failed to metabolize formate to H 2 and CO 2 [116].…”

“…Nitrogenase activity was stimulated by the addition of ferredoxin, indicating the presence of a pyruvate-dependent ferredoxin reductase. Finally, mutants with altered pigmentation accumulate after long-term anaerobic growth in the dark, and these mutants appear to metabolize pyruvate differently from the wild-type [114,118].…”

Optimization of the Sistrom Culture Medium for Large-Scale Batch Cultivation of Rhodospirillum rubrum under Semiaerobic Conditions with Maximal Yield of Photosynthetic Membranes

“…The phototrophic purple non-sulfur bacterium, Rhodospirillum rubrum, will grow with a wide variety of carbon and energy sources under aerobic, anaerobic, or fermentative conditions (1,(5)(6)(7)(9)(10)(11). In recent years, mutants which have lost some component of the photosynthetic apparatus but which are still able to form the specialized intracytoplasmic membranes containing the photosynthetic apparatus have become an indispensable tool for the study of structure-function relationships (4).…”