Nonacetogenic Growth of the Acetogen Acetobacterium woodii on 1,2-Propanediol

Acetogenic bacteria can grow by the oxidation of various substrates coupled to the reduction of CO₂ in the Wood-Ljungdahl pathway. Here, we show that growth of the acetogen Acetobacterium woodii on 1,2-propanediol (1,2-PD) as the sole carbon and energy source is independent of acetogenesis. Enzymatic measurements and metabolite analysis revealed that 1,2-PD is dehydrated to propionaldehyde, which is further oxidized to propionyl coenzyme A (propionyl-CoA) with concomitant reduction of NAD. NADH is reoxidized by reducing propionaldehyde to propanol. The potential gene cluster coding for the responsible enzymes includes genes coding for shell proteins of bacterial microcompartments. Electron microscopy revealed the presence of microcompartments as well as storage granules in cells grown on 1,2-PD. Gene clusters coding for the 1,2-PD pathway can be found in other acetogens as well, but the distribution shows no relation to the phylogeny of the organisms.     

A Bacterial Electron-bifurcating Hydrogenase

The Wood-Ljungdahl pathway of anaerobic CO(2) fixation with hydrogen as reductant is considered a candidate for the first life-sustaining pathway on earth because it combines carbon dioxide fixation with the synthesis of ATP via a chemiosmotic mechanism. The acetogenic bacterium Acetobacterium woodii uses an ancient version of the pathway that has only one site to generate the electrochemical ion potential used to drive ATP synthesis, the ferredoxin-fueled, sodium-motive Rnf complex. However, hydrogen-based ferredoxin reduction is endergonic, and how the steep energy barrier is overcome has been an enigma for a long time. We have purified a multimeric [FeFe]-hydrogenase from A. woodii containing four subunits (HydABCD) which is predicted to have one [H]-cluster, three [2Fe2S]-, and six [4Fe4S]-clusters consistent with the experimental determination of 32 mol of Fe and 30 mol of acid-labile sulfur. The enzyme indeed catalyzed hydrogen-based ferredoxin reduction, but required NAD(+) for this reaction. NAD(+) was also reduced but only in the presence of ferredoxin. NAD(+) and ferredoxin reduction both required flavin. Spectroscopic analyses revealed that NAD(+) and ferredoxin reduction are strictly coupled and that they are reduced in a 1:1 stoichiometry. Apparently, the multimeric hydrogenase of A. woodii is a soluble energy-converting hydrogenase that uses electron bifurcation to drive the endergonic ferredoxin reduction by coupling it to the exergonic NAD(+) reduction.     

Collecting history of the hummingbird genera Chaetocercus Gray, 1855 and Lophornis Lesson, 1829

We examined the Chaetocercus and Lophornis holdings of 21 European, US and South American avian collections. Only skin specimens with exact (to the year) collecting dates and reliable locality data on their labels, which could be checked personally, were analysed. We located 466 Chaetocercus and 373 Lophornis specimens collected between the years 1859 and 1999. The vast majority of these records are old ones, dated between 1880 and 1960: 93% of the Chaetocercus and 82% of the Lophornis study skins. Less than 1% of all specimens was obtained after 1990. Potential explanations for our findings, such as declining population levels of these hummingbird genera, historically changing collecting activities regarding commercial dealers and collecting techniques, and legal collecting restrictions are discussed. Our findings reflect a general trend of decreasing collecting activities worldwide.Communicated by F. Bairlein     

Somatic embryogenesis of tissue cultures of Papaver somniferum and Papaver orientale and its relationship to alkaloid and lipid metabolism

Transfer from complete to 2,4-D free Gamborg's B5-medium efficiently induced somatic embryogenesis in Papaver tissue cultures (P. somniferum and P. orientale). Embryogenesis was preceded by a strong temporary accumulation of triacylglycerols. In both tissue cultures large amounts of sanguinarine type alkaloids were present, which disappeared during regeneration in the P. orientale cultures but persisted in the P. somniferum cultures. In the P. somniferum cultures protopine and morphine type alkaloids (morphine, codeine, thebaine) appeared about 45 days after exchanging the medium. Thebaine was the main alkaloid in the P. somniferum embryoids accumulating up to 0.2 % of dry weight.     

Energieumsatz in Abh?ngigkeit von der Umgebungstemperatur beim KolibriOcreatus u. underwoodii

Zusammenfassung Bei der südamerikanischen KolibriartOcreatus u. underwoodii (2.7 g±0.09 SD, n=3) wurde der Ruhe- und Flugstoffwechsel in Abhängigkeit von der Umgebungstemperatur (3° bis 34° C) bei Licht und ohne Nahrungsentzug untersucht, sowie der stündliche Energieverbrauch ermittelt.1. Der Ruhestoffwechsel stieg linear bei fallender Umgebungstemperatur (r=0.95±0.04 SD, n=3).2. Der Flugstoffwechsel zeigte eine dem Ruhestoffwechsel entsprechende Abhängigkeit von der Umgebungstemperatur.3. FürOcreatus u. underwoodii wurden für Sitzen bzw. Fliegen mit 199.2 mW/g bzw. 325.3 mW/g die höchsten für homöotherme Tiere bisher ermittelten Wärmeproduktionsraten gemessen.4. Im getesteten Umgebungstemperaturbereich schwankte die Körpertemperatur bei den drei Individuen zwischen 38.8° und 39.9° C.5. Der für 25° C Umgebungstemperatur berechnete Energieverbrauch betrug ca. 1030 J/h.6. Zur Deckung des Energiebedarfs mußOcreatus u. underwoodii stündlich z. B. 205Salvia-Blüten besuchen.

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Energetical responses to various ambient temperatures in the hummingbirdOcreatus u. underwoodii

Summary Metabolism of resting and flyingOcreatus u. underwoodii (2.7 g±0.09 SD, n=3) was measured at varying ambient temperatures (3°–34° C). All experiments were conducted in light. In the metabolic chamber the bird had access to food. The caloric expenses were calculated for one hour.1. Metabolism of restingOcreatus u. underwoodii increased linearly with falling ambient temperature (r=0.95±0.04 SD, n=3).2. During flight O₂-consumption showed the same relation to ambient temperature as in resting birds.3 With 199.2 mW/g for resting and 325.3 mW/g for flight the highest rates for heat production in homeothermic animals were registrated.4. In the tested range of ambient temperature body temperature varied in all 3 individuals from 38.8° to 39.9° C.5. The caloric expenses at 25° C ambient temperature, the most commonly experienced temperature in the natural environment of this hummingbird species, were about 1030 J/h.6. To gain its energy requirementsOcreatus u. underwoodii has to visit e. g. about 205 Salvia flowers per hour.

     

The SO4(.-)-induced chain reaction of 1,3-dimethyluracil with peroxodisulphate

The sulphate radical SO4(.-) reacts with 1,3-dimethyluracil (1,3-DMU) (k = 5 X 10(9) dm3 mol-1 s-1) thereby forming with greater than or equal to 90 per cent yield the 1,3-DMU C(5)-OH adduct radical 4 as evidenced by its absorption spectrum and its reactivity toward tetranitromethane. Pulse-conductometric experiments have shown that a 1,3-DMU-SO4(.-) aduct 3 as well as the 1,3-DMU radical cation 1, if formed, must be very short-lived (t1/2 less than or equal to 1 microsecond). The 1,3-DMU C(5)-OH adduct 4 reacts slowly with peroxodisulphate (k = 2.1 X 10(5) dm3 mol-1 s-1). It is suggested that the observed new species is the 1,3-DMU-5-OH-6-SO4(.-) radical 7. At low dose rates a chain reaction is observed. The product of this chain reaction is the cis-5,6-dihydro-5,6-dihydroxy-1,3-dimethyluracil 2. At a dose rate of 2.8 X 10(-3) Gys-1 a G value of approximately 200 was observed ([1,3-DMU] = 5 X 10(-3) mol dm-3; [S2O8(2-)] = 10(-2) mol dm-3; [t-butanol] = 10(-2) mol dm-3). The peculiarities of this chain reaction (strong effect of [1,3-DMU], smaller effect of [S2O(2-)8]) is explained by 7 being an important chain carrier. It is proposed that 7 reacts with 1,3-DMU by electron transfer, albeit more slowly (k approximately 1.2 X 10(4) dm3 mol-1 s-1) than does SO4(.-). The resulting sulphate 6 is considered to hydrolyse into 2 and sulphuric acid which is formed in amounts equivalent to those of 2. Computer simulations provide support for the proposed mechanism. The results of some SCF calculations on the electron distribution in the radical cations derived from uracil and 1-methyluracil are also presented.