PHYSIOLOGICAL AND BIOCHEMICAL-CHANGES ACCOMPANYING THE LOSS OF MUCOIDY BY PSEUDOMONAS-AERUGINOSA

Pseudomonas aeruginosa M60, a mucoid strain, was grown in continuous c ulture (D 0.05 h(-1)) under ammonia limitation with glucose as the car bon source. Steady-state alginate production occurred for only 1-2 d u nder these conditions [q(alginate) 0.097 g alginate h(-1) (g dry wt ce lls)(-1)], after which time the percentage of mucoid cells and the alg inate concentration in the culture decreased in parallel and approache d zero after approximately 10 d. These changes were accompanied by sim ilar 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 'extern al' non-phosphorylative pathway of glucose metabolism, glucose dehydro genase. In contrast, the activities of other enzymes associated with t his pathway (gluconate dehydrogenase, 2-ketogluconate kinase plus 2-ke togluconate-6-phosphate reductase) or with the 'internal' phosphorylat ive pathway of glucose metabolism (glucokinase and glucose-6-phosphate dehydrogenase) remained essentially unchanged. The loss of mucoidy an d alginate production was accompanied by the appearance of low concent rations of Intracellular polyhydroxyalkanoate (PHA) and of extracellul ar gluconate and 2-ketogluconate (partly at the expense of alginate pr oduction and partly as a result of increased glucose consumption). It is suggested that ammonia-limited, glucose-excess cultures of P. aerug inosa growing at low dilution rate are unable fully to regulate the ra te at which glucose and/or its 'external' pathway metabolites are take n up by the cell, and therefore form copious amounts of alginate in or der both to overcome the potentially deleterious osmotic effects of ac cumulating surplus intracellular metabolites and to consume the surplu s ATP generated by the further oxidation of these metabolites. The los s of mucoidy invokes the use of an alternative, but analogous, strateg y via which non-mucoid cells produce an osmotically inactive intracell ular product (PHA) plus increased amounts of the extracellular metabol ites gluconate and 2-ketogluconate via the low-energy-yielding and, un der these conditions, largely dead-end 'external' metabolic pathway.