Dependence of fluorescence behaviour and other photosystem-II characteristics on the nature of the nitrogen source for the filamentous cyanobacterium Oscillatoria chalybea

The filamentous cyanobacterium Oscillatoria chalybea grows phototrophically on a mineral medium in the presence of either nitrate or ammonium ions as nitrogen source at similar growth rates. In the absence of any combined nitrogen source in the medium the cyanobacterium also grows, although at a reduced growth rate. The steady state rate of oxygen evolution by filaments from these three culture conditions is approximately constant if compared on an equal chlorophyll basis. Qualitative differences, however, emerge, if transient phenomena, e.g. the oxygen gush, are investigated. Only nitrate-and nitrogen-free-grown cultures show an oxygen gush, whereas ammonium sulfate-grown cultures do not show this phenomenon. Fluorescence induction in O. chalybea shows a fast monophasic rise, comparable to the fluorescence rise curves of higher plant chloroplasts in the presence of dithionite. The steady state level of fluorescence in ammonium sulfate-grown cells is up to seven times higher than in nitrate-grown cells when compared on an equal chlorophyll basis. In ammonium sulfate-grown cells, DCMU (N,N-3,4-Dichlorophenyl dimethylurea) causes a further increase in fluorescence level. In nitrate-grown cyanobacteria, however, the effect of DCMU consists of a decrease of the steady state level of fluorescence. In context with earlier research on Anabaena cylindrica, another filamentous cyanobacterium, it appears that the type of the nitrogen source used for growth determines the main location of the DCMU-block in this organism. It thus appears that in O. chalybea the site of DCMU inhibition lies on the oxygen-evolving side of photosystem II, if the organism is grown on nitrate. If grown on ammonium sulfate, no substantial difference of the location of the inhibition site when compared to algae or higher plant chloroplasts is found.Thylakoid preparations of O. chalybea perform the usual Hill reactions with ferricyanide, p-benzoquinone or silicomolybdate as electron acceptors. In each case it is seen that with thylakoids of nitrate-grown cells the steady-state level of fluorescence is lowered by DCMU in the presence of these acceptors, which should be the case, if DCMU inhibits electron transfer on the donor side of photosystem II. According to the literature silicomolybdate accepts electrons mainly before the DCMU-block in higher plant chloroplasts. Hence, in higher plants this reaction is mainly DCMU-insensitive. In thylakoids of O. chalybea, however, the Hill reaction with silicomolybdate is DCMU-sensitive which provides further evidence that the DCMU-block is on the oxygen-evolving side of photosystem II in O. chalybea provided the cells have been grown on nitrate.Abbreviations DCMU N-N-3,4-Dichlorophenyl dimethylurea     

Parameters of unbalanced growth and reversible inhibition of deoxyribonucleic acid synthesis in Brevibacterium ammoniagenes ATCC 6872 induced by depletion of Mn2+. Inhibitor studies on the reversibility of deoxyribonucleic acid synthesis

Unbalanced growth induced by depletion of manganese ions was a prerequisite for production of ribonucleotides in a high salt mineral medium with the wildtype strain Brevibacterium ammoniagenes ATCC 6872. The concentration of manganese strictly controlled the overall deoxyribonucleic acid (DNA) synthesis, whereas ribonucleic acid (RNA), protein and cell wall synthesis remained essentially unimpaired in the manganese-lacking cells.The reversibility of inhibition of overall DNA synthesis was shown by enhanced incorporation (up to threefold compared to the cultures supplied with sufficient manganese) of [8-¹⁴C] adenine into alkali-stable, trichloroacetic acid-insoluble material after subsequent addition of 10 M MnCl₂ to 15 h-old depleted cultures.The results of inhibitor studies on the restoration of overall DNA synthesis due to subsequent addition of manganese ions to depleted cultures suggest that ribonucleotide reduction is the primary target of the manganese starvation during nucleotide fermentation with Brevibacterium ammoniagenes ATCC 6872.     

The influence of cholesterol on head group mobility in phospholipid membranes

The dielectric dispersion in the MHz range of the zwitterionic dipolar phosphocholine head groups has been measured from 0–70°C for various mixtures of $\text{1,2-}\text{dipalmitoyl}\text{-sn-}\text{glycero-3-phosphocholine}$ (DPPC) and cholesterol. The abrupt change in the derived relaxation frequency $\text{f}{}_2$ observed for pure DPPC at the gel-to-liquid crystalline phase transition at 42°C reduces to a more gradual increase of frequency with temperature as the cholesterol content is increased. In general the presence of cholesterol increases the DPPC head group mobility due to its spacing effect. Below 42°C no sudden changes in $\text{f}{}_2$ are found at 20 or 33 mol% cholesterol, where phase boundaries have been suggested from other methods. Above 42°C, however, a decrease in $\text{f}{}_2$ at cholesterol contents up to 20–30 mol% is found. This is thought to be partly due to an additional restricting effect of the cholesterol on the number of hydrocarbon chain conformations and consequently on the area occupied by the DPPC molecules.     

Pyruvate fermentation in Rhodospirillum rubrum and after transfer from aerobic to anaerobic conditions in the dark

The fermentative metabolism of Rhodospirillum rubrum (strain Ha, F₁, S₁) was studied after transfering the cells from aerobic to anaerobic dark culture conditions. Pyruvate was metabolized mainly to acetate and formate, and to a lesser extent to CO₂ and propionate, by all strains. Therefore, pyruvate formate lyase would appear to be the characteristic key enzyme of the dark anaerobic fermentation metabolism in R. rubrum. Strain F₁ and S₁ metabolized the formate further to H₂ and CO₂. It is concluded that this cleavage was catalysed by a formate hydrogen lyase system. Strain Ha was unable to metabolize formate. The cleavage of formate and the synthesis of poly--hydroxy-butyric acid were increased by a low pH value (6.5). Fermentation equations and schemes of the pyruvate metabolism are discussed.     

Glucose-6-phosphate-dependent pyruvate kinase in Streptococcus mutans.

Pyruvate kinase of Streptococcus mutans JC 2 had an absolute and specific requirement for glucose-6-phosphate. Inorganic phosphate was a strong inhibitor. The enzyme required K+ or NH4+ and Mg2+ or Mn2+. S. mutans FIL and E 49, Streptococcus bovis ATCC 9809, and Streptococcus salivarius ATCC 13419 had also glucose-6-phosphate-dependent pyruvate kinases, whereas Streptococcus sanguis NCTC 10904 had an enzyme activated by fructose-1,6-diphosphate.