Glucose and galactose metabolism in Gluconabacter liquefaciens

Glucose-grown cells of Gluconobacter liquefaciens oxidize glucose, gluconate and 2-ketogluconate practically completely to 2,5-diketogluconate by particulate enzymes, localized in the protoplasmic membrane. The bulk of the 2,5-diketgluconate (and 5-ketogluconate) enters the cytoplasm and is metabolized after reduction to gluconate by soluble enzymes. The gluconate is then phosphorylated and metabolized by the enzymes of the pentosephosphate cycle. The particulate enzymes do not participate in the metabolism of this gluconate because of their localization. A small part of the 2,5-diketogluconate is slowly ozidized by the particles to rubiginol (3,5=dihydroxy-4-ketopyran), which gives upon decomposition the brown colouration, which is characteristics for this strain grown in a glucose-chalk medium. The formation of 2,5-diketogluconate and of brown pigments only occurs with glucose-grown cells and is dependent on the induction of the adaptive enzyme 2-ketogluconooxydase in the protoplasmic membrane. By growth on a galactose medium a 2-keto-3-deoxygalactonokinase is induced. Galactose is broken down with galactonate, 2-keto-3-deoxygalactonate and its phosphate ester as intermediates. Pyruvate and triosephosphate are the ultimate reaction products of this system (Fig. 14). In galactose-grown cells no 2-ketogluconooxydase is present in the protoplasmic membrane. No 2,5-diketogluconate and no brown pigments are formed. In these cells glucose and gluconate are oxidized after phosphorylation

Energy production in Gluconobacter liquefaciens

Energy production in Gl. liquefaciens was studied by measuring oxidative phosphorylation in cell-free extracts and molar growth yield in growing cultures. P/O ratios were found very low and ranged from 0.09 for DPNH to 0.40 for glucose 6-phosphate, that is about 5% of the efficiency in animal mitochondria. The low P/O ratios truly represent the low efficiency of energy transfer in this organism, as in growing cultures the molar growth yield is equally low. From the P/O ratio and the molar growth yield for the oxidation from ethanol to acetate the yield in milligram dry cells/mole of ATP produced was calculated at 10 mg/mmole ATP. This value is in close agreement with that reported for other microorganisms. The low efficiency of energy transfer is partly explained by the presence of only one cytochrome in this organism. The absence of respiratory control (indicated by insensitivity to DNP) suggests that the oxidation is very loosely coupled to phosphorylation

Purification and genetic determination of bacteriocin production in Enterobacter cloacac

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Super Life: how and why 'cell selection' leads to the fastest growing eukaryote.

What is the highest possible replication rate for living organisms? The cellular growth rate is controlled by a variety of processes. Therefore, it is unclear which metabolic process or group of processes should be activated to increase growth rate. An organism that is already growing fast may already have optimized through evolution all processes that could be optimized readily, but may be confronted with a more generic limitation. Here we introduce a method called 'cell selection' to select for highest growth rate, and show how such a cellular site of 'growth control' was identified. By applying pH-auxostat cultivation to the already fast-growing yeast Kluyveromyces marxianus for a sufficiently long time, we selected a strain with a 30% increased growth rate; its cell-cycle time decreased to 52 min, much below that reported to date for any eukaryote. The increase in growth rate was accompanied by a 40% increase in cell surface at a fairly constant cell volume. We show how the increase in growth rate can be explained by a dominant (80%) limitation of growth by the group of membrane processes (a 0.7% increase of specific growth rate to a 1% increase in membrane surface area). Simultaneous activation of membrane processes may be what is required to accelerate growth of the fastest-growing form of eukaryotic life to growth rates that are even faster, and may be of potential interest for single-cell protein production in industrial 'White' biotechnology processes. © 2008 The Authors

Note: Physiological aspects of the growth of the lactic acid bacterium Tetragenococcus halophila during Indonesian soy sauce

The lactic acid bacterium Tetragenococcus halophila is the dominant species in Indonesian soy mash. Tetragenococcus halophila growing in continuous and retention cultures under defined glucose-limited conditions showed a switch from homolactic (only lactate produced) to mixed acid fermentation (two formate, one acetate and one ethanol formed per glucose) at low growth rates. However, despite low concentrations of sugars present in soy mash and slow growth, no switch to mixed acid fermentation was observed during growth in soy mash. The absence of mixed acid fermentation could not be explained by changes in pH or lactate concentration during growth, indicating that growth in soy mash is not energy-limited. Despite the absence of mixed acid fermentation, an obvious production of acetate, an important soy mash component, is observed in soy mash. The possibility that soy mash components acting as hydrogen acceptors could account for this phenomenon is discussed

Respiration-driven proton translocation with nitrite and nitrous oxide in Paracoccus denitrificans

(1)H+ leads to/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O2, NO2- or N2O. Under optimal H+-translocation conditions, the ratios leads to H+/O, H+ leads to/N2O, H+ leads to/NO2- for reduction to N2 and H+ leads to/NO2- for reduction to N2O were 6.0-6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N,'N'-tetramethyl-p-phenylene-diamine as exogenous substrate, addition of NO2- or N2O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. H+/N2O, H+/NO2- for reduction to N2 and H+/NO2- for reduction to N2O were -0.84, -2.33 and -1.90, respectively. (3) The H+/oxidant ratios, mentioned in item 2, were not altered in the presence of valinomycin/K+ and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O2, NO2- and N2O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO2-, N2O or O2 pass two H+-trans-locating sites. The H+ leads to/electron acceptor ratios predicted by this scheme are in good agreement with the experimental values