title: The effect of the dissolved oxygen concentration and anabolic limitations on the behaviour of Rhizobium ORS571 in chemostat cultures.
abstract: Chemostat cultures of Rhizobium ORS571 limited by the supply of oxygen or an anabolic substrate contained poly-beta-hydroxybutyrate (PHB). Low amounts of PHB (about 10%) were present in ammonia- or nitrate-limited cultures; higher amounts were found in Mg++-limited cultures (about 20%) and in oxygen-limited nitrogen-fixing cultures (37%). A method is described to calculate YATP values (g PHB-free biomass . mol-1 ATP) from the Ysucc values (g dry wt . mol-1 succinate) measured. Ysucc and YATP values in cultures limited by the supply of an anabolic substrate and in the oxygen-limited ammonia-assimilating culture were much lower than the values found in the PHB-free succinate-limited cultures. This shows that uncoupling of growth and energy production occurred. Therefore, H2/N2 ratio (mol hydrogen formed per mol nitrogen fixed) in nitrogen-fixing cultures could not be calculated from the comparison of the YATP value found in the nitrogen-fixing culture and the value found in the corresponding ammonia-assimilating culture. Although the optimal dissolved oxygen concentration (d.o.c.) for nitrogen-fixing cultures of Rhizobium ORS571 is 5 or 10 microM, nitrogen-fixing cultures could be obtained up to a d.o.c. of 40 microM. Not only nitrogenase but also hydrogenase was active at this d.o.c. However, accumulation of PHB (10%) may indicate that cultures grown at unfavourable oxygen concentrations (15-40 microM O2) were N-limited rather than energy-limited, which may be the result of partial inactivation or repression of nitrogenase at a higher d.o.c.
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000641:Ammonia / Q000378:metabolism; D003470:Culture Media; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000378:metabolism; D006885:Hydroxybutyrates / Q000096:biosynthesis*; D008274:Magnesium / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009591:Nitrogenase / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D011091:Polyesters; D011108:Polymers / Q000096:biosynthesis*; D012231:Rhizobium / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D000094122:Polyhydroxybutyrates
chemical_list: D000255:Adenosine Triphosphate; D000641:Ammonia; D003470:Culture Media; D006859:Hydrogen; D006864:Hydrogenase; D006885:Hydroxybutyrates; D008274:Magnesium; D009566:Nitrates; D009584:Nitrogen; D009591:Nitrogenase; D010100:Oxygen; D011091:Polyesters; D011108:Polymers; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates