Williams Steven G, Greenwood Jacqueline A, Jones Colin W
Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK.
Microbiology (Reading). 1996 Apr;142 ( Pt 4):881-888. doi: 10.1099/00221287-142-4-881.
Pseudomonas aeruginosa M60, a mucoid strain, was grown in continuous culture (D 0.05 h-1) under ammonia limitation with glucose as the carbon source. Steady-state alginate production occurred for only 1-2 d under these conditions [qalginate 0.097 g alginate h-1 (g dry wt cells)-1], after which time the percentage of mucoid cells and the alginate concentration in the culture decreased in parallel and approached zero after approximately 10 d. These changes were accompanied by similar decreases in the activities of the alginate biosynthetic enzymes (represented by phosphomannomutase and GDP-mannose dehydrogenase) and by a large increase in the activity of the first enzyme of the 'external' non-phosphorylative pathway of glucose metabolism, glucose dehydrogenase. In contrast, the activities of other enzymes associated with this pathway (gluconate dehydrogenase, 2-ketogluconate kinase plus 2-ketogluconate-6-phosphate reductase) or with the 'internal' phosphorylative pathway of glucose metabolism (glucokinase and glucose-6-phosphate dehydrogenase) remained essentially unchanged. The loss of mucoidy and alginate production was accompanied by the appearance of low concentrations of intracellular polyhydroxyalkanoate (PHA) and of extracellular gluconate and 2-ketogluconate (partly at the expense of alginate production and partly as a result of increased glucose consumption). It is suggested that ammonia-limited, glucose-excess cultures of P. aeruginosa growing at low dilution rate are unable fully to regulate the rate at which glucose and/or its 'external' pathway metabolites are taken up by the cell, and therefore form copious amounts of alginate in order both to overcome the potentially deleterious osmotic effects of accumulating surplus intracellular metabolites and to consume the surplus ATP generated by the further oxidation of these metabolites. The loss of mucoidy invokes the use of an alternative, but analogous, strategy via which non-mucoid cells produce an osmotically inactive intracellular product (PHA) plus increased amounts of the extracellular metabolites gluconate and 2-ketogluconate via the low-energy-yielding and, under these conditions, largely dead-end 'external' metabolic pathway.
黏液型铜绿假单胞菌M60在以葡萄糖为碳源、氨受限的条件下进行连续培养（稀释率D为0.05 h⁻¹）。在这些条件下，稳态藻酸盐产生仅持续1 - 2天[藻酸盐合成速率qalginate为0.097 g藻酸盐·h⁻¹·(g干重细胞)⁻¹]，此后黏液型细胞百分比和培养物中藻酸盐浓度平行下降，约10天后接近零。这些变化伴随着藻酸盐生物合成酶（以磷酸甘露糖变位酶和GDP - 甘露糖脱氢酶为代表）活性的类似下降，以及葡萄糖代谢“外部”非磷酸化途径的首个酶葡萄糖脱氢酶活性的大幅增加。相比之下，与该途径相关的其他酶（葡萄糖酸脱氢酶、2 - 酮葡萄糖酸激酶加2 - 酮葡萄糖酸 - 6 - 磷酸还原酶）或与葡萄糖代谢“内部”磷酸化途径相关的酶（葡萄糖激酶和葡萄糖 - 6 - 磷酸脱氢酶）的活性基本保持不变。黏液性丧失和藻酸盐产生的减少伴随着低浓度细胞内聚羟基脂肪酸酯（PHA）以及细胞外葡萄糖酸和2 - 酮葡萄糖酸的出现（部分以藻酸盐产生为代价，部分是葡萄糖消耗增加的结果）。有人提出，在低稀释率下生长的氨受限、葡萄糖过量的铜绿假单胞菌培养物无法完全调节细胞摄取葡萄糖和/或其“外部”途径代谢物的速率，因此形成大量藻酸盐，以便既克服积累的细胞内多余代谢物潜在的有害渗透效应，又消耗这些代谢物进一步氧化产生的多余ATP。黏液性的丧失引发了一种替代但类似的策略，通过该策略非黏液型细胞产生一种无渗透活性的细胞内产物（PHA），并通过低能量产生且在这些条件下基本为无出路的“外部”代谢途径增加细胞外代谢物葡萄糖酸和2 - 酮葡萄糖酸的量。
