de Vries W, Stam H, Duys J G, Ligtenberg A J, Simons L H, Stouthamer A H
Antonie Van Leeuwenhoek. 1986;52(1):85-96. doi: 10.1007/BF00402690.
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.
由氧气或合成代谢底物供应受限的根瘤菌ORS571恒化器培养物中含有聚-β-羟基丁酸酯（PHB）。在氨或硝酸盐受限的培养物中存在少量的PHB（约10%）；在镁离子受限的培养物中发现了更高含量（约20%），在氧气受限的固氮培养物中含量为37%。描述了一种根据所测得的Ysucc值（克干重·摩尔⁻¹琥珀酸）计算YATP值（克无PHB生物量·摩尔⁻¹ATP）的方法。在由合成代谢底物供应受限的培养物以及氧气受限的氨同化培养物中的Ysucc和YATP值远低于在无PHB的琥珀酸受限培养物中所发现的值。这表明生长与能量产生发生了解偶联。因此，固氮培养物中的H₂/N₂比率（每固定1摩尔氮形成的氢气摩尔数）无法通过比较固氮培养物中发现的YATP值与相应氨同化培养物中发现的值来计算。尽管根瘤菌ORS571固氮培养物的最佳溶解氧浓度（d.o.c.）为5或10微摩尔，但在高达40微摩尔的d.o.c.下仍可获得固氮培养物。在此d.o.c.下不仅固氮酶而且氢化酶都具有活性。然而，PHB的积累（10%）可能表明在不利的氧气浓度（15 - 40微摩尔O₂）下生长的培养物是氮受限而非能量受限的，这可能是由于在较高d.o.c.下固氮酶部分失活或受到抑制的结果。
