Senior P J, Beech G A, Ritchie G A, Dawes E A
Biochem J. 1972 Aug;128(5):1193-201. doi: 10.1042/bj1281193.
Azotobacter beijerinckii was grown in ammonia-free glucose-mineral salts media in batch culture and in chemostat cultures limited by the supply of glucose, oxygen or molecular nitrogen. In batch culture poly-beta-hydroxybutyrate was formed towards the end of exponential growth and accumulated to about 74% of the cell dry weight. In chemostat cultures little poly-beta-hydroxybutyrate accumulated in organisms that were nitrogen-limited, but when oxygen limited a much increased yield of cells per mol of glucose was observed, and the organisms contained up to 50% of their dry weight of poly-beta-hydroxybutyrate. In carbon-limited cultures (D, the dilution rate,=0.035-0.240h(-1)), the growth yield ranged from 13.1 to 19.8g/mol of glucose and the poly-beta-hydroxybutyrate content did not exceed 3.0% of the dry weight. In oxygen-limited cultures (D=0.049-0.252h(-1)) the growth yield ranged from 48.4 to 70.1g/mol of glucose and the poly-beta-hydroxybutyrate content was between 19.6 and 44.6% of dry weight. In nitrogen-limited cultures (D=0.053-0.255h(-1)) the growth yield ranged from 7.45 to 19.9g/mol of glucose and the poly-beta-hydroxybutyrate content was less than 1.5% of dry weight. The sudden imposition of oxygen limitation on a nitrogen-limited chemostat culture produced a rapid increase in poly-beta-hydroxybutyrate content and cell yield. Determinations on chemostat cultures revealed that during oxygen-limited steady states (D=0.1h(-1)) the oxygen uptake decreased to 100mul h(-1) per mg dry wt. compared with 675 for a glucose-limited culture (D=0.1h(-1)). Nitrogen-limited cultures had CO(2) production values in situ ranging from 660 to 1055mul h(-1) per mg dry wt. at growth rates of 0.053-0.234h(-1) and carbon-limited cultures exhibited a variation of CO(2) production between 185 and 1328mul h(-1) per mg dry wt. at growth rates between 0.035 and 0.240h(-1). These findings are discussed in relation to poly-beta-hydroxybutyrate formation, growth efficiency and growth yield during growth on glucose. We suggest that poly-beta-hydroxybutyrate is produced in response to oxygen limitation and represents not only a store of carbon and energy but also an electron sink into which excess of reducing power can be channelled.
拜氏固氮菌在无氨的葡萄糖 - 矿物盐培养基中进行分批培养，并在以葡萄糖、氧气或分子氮供应受限的恒化器培养中生长。在分批培养中，聚 - β - 羟基丁酸在指数生长末期形成，并积累至细胞干重的约74%。在恒化器培养中，在氮受限的生物体中几乎没有聚 - β - 羟基丁酸积累，但当氧气受限时，每摩尔葡萄糖的细胞产量显著增加，并且生物体中聚 - β - 羟基丁酸含量高达其干重的50%。在碳受限培养（稀释率D = 0.035 - 0.240h⁻¹）中，生长产量范围为每摩尔葡萄糖13.1至19.8克，聚 - β - 羟基丁酸含量不超过干重的3.0%。在氧气受限培养（D = 0.049 - 0.252h⁻¹）中，生长产量范围为每摩尔葡萄糖48.4至70.1克，聚 - β - 羟基丁酸含量为干重的19.6%至44.6%。在氮受限培养（D = 0.053 - 0.255h⁻¹）中，生长产量范围为每摩尔葡萄糖7.45至19.9克，聚 - β - 羟基丁酸含量小于干重的1.5%。对氮受限的恒化器培养突然施加氧气限制会导致聚 - β - 羟基丁酸含量和细胞产量迅速增加。对恒化器培养的测定表明，在氧气受限的稳定状态（D = 0.1h⁻¹）下，氧气摄取量降至每毫克干重100微升/小时，而葡萄糖受限培养（D = 0.1h⁻¹）为675微升/小时。氮受限培养原位二氧化碳产生值在生长速率为0.053 - 0.234h⁻¹时范围为每毫克干重660至1055微升/小时，碳受限培养在生长速率为0.035至0.240h⁻¹时二氧化碳产生量在每毫克干重185至1328微升/小时之间变化。这些发现结合葡萄糖生长过程中的聚 - β - 羟基丁酸形成、生长效率和生长产量进行了讨论。我们认为聚 - β - 羟基丁酸是对氧气限制的响应产物，不仅代表碳和能量的储存，还代表一个电子汇，过量的还原力可以导入其中。
