Baev M V, Kiriukhin M Y, Tsygankov Y D
Institute for Genetics and Selection of Industrial Microorganisms, Moscow, Russia.
Antonie Van Leeuwenhoek. 1997 May;71(4):353-61. doi: 10.1023/a:1000293619500.
The obligate methylotroph Methylobacillus flagellatum was grown in the presence of different ammonium concentrations and the regulation of the enzymes associated with ammonium assimilation was investigated in steady-state and transient growth regimes. As the medium changed from C-limitation to dual C/N- and finally to N-limitation, the culture passed through three definite growth phases. The NADP(+)-dependent glutamate dehydrogenase (GDH) was present under ammonium limitation of the culture growth (at 2 mmol 1(-1) of ammonium in the growth medium) and increased in response to an increase in nitrogen availability. Glutamine synthetase (GS) and glutamate synthase (GOGAT) activities were negligible during C- and C/N-limitation. In N-limited cells the GOGAT activity increased as the dilution rate increased up to 0.35 h-1, and then sharply dropped. In the N-sufficient cultures both NAD(+)-and NADP(+)-dependent isocitrate dehydrogenase (NAD-ICDH and NADP-ICDH) activities were up-regulated as dilution rate increased, but in the N-limited culture the NAD-ICDH activity was up-regulated whereas NADP-ICDH one was down-regulated. Pulse additions of ammonium and methanol demonstrated the coordinate regulation of the GDH and ICDHs activities. When pulses were added to the C/N-limited cultures, there was an immediate utilization of the nutrients, resulting in an increase in biomass; at the same time the GDH and ICDH activities increased and the GS and GOGAT activities decreased. When the same ammonium/methanol pulse was added into the N-limited culture, there was a 3 h delay in the culture response, after which the substrates were utilized at rates close to the ones shown by the C/N-limited culture after the analogous pulse.
专性甲基营养菌鞭毛甲基杆菌在不同铵浓度下培养，并在稳态和瞬态生长模式下研究了与铵同化相关酶的调控。随着培养基从碳限制转变为碳/氮双重限制，最终变为氮限制，培养物经历了三个明确的生长阶段。依赖NADP(+)的谷氨酸脱氢酶（GDH）在培养物生长的铵限制条件下（生长培养基中铵浓度为2 mmol 1(-1)）存在，并随着氮可利用性的增加而增加。谷氨酰胺合成酶（GS）和谷氨酸合酶（GOGAT）的活性在碳限制和碳/氮限制期间可忽略不计。在氮限制的细胞中，GOGAT活性随着稀释率增加至0.35 h-1而增加，然后急剧下降。在氮充足的培养物中，随着稀释率增加，依赖NAD(+)和NADP(+)的异柠檬酸脱氢酶（NAD-ICDH和NADP-ICDH）的活性均上调，但在氮限制培养物中，NAD-ICDH活性上调而NADP-ICDH活性下调。铵和甲醇的脉冲添加证明了GDH和ICDHs活性的协同调控。当向碳/氮限制的培养物中添加脉冲时，营养物质立即被利用，导致生物量增加；同时GDH和ICDH活性增加，而GS和GOGAT活性降低。当将相同的铵/甲醇脉冲添加到氮限制的培养物中时，培养物的反应延迟3小时，之后底物的利用速率接近类似脉冲后碳/氮限制培养物所显示的速率。
