PHOSPHATE-UPTAKE BEHAVIOR OF A MUTANT OF SYNECHOCOCCUS SP. PCC-7942 LACKING ONE PROTEIN OF THE HIGH-AFFINITY PHOSPHATE-UPTAKE SYSTEM

The phosphate-uptake behaviour of a sphX mutant of the cyanobacterium Synechococcus leopoliensis (Raciborski) Komarek, strain PCC 7942 has b een studied. This mutant lacks the high-affinity phosphate-binding pro tein that is abundantly expressed under phosphate-deficient growth con ditions. The following observations have been made: (i) The mutant is still capable of utilizing phosphate at nanomolar external concentrati ons. (ii) Elimination of the sphX gene leads to an increase in the Mic haelis constant and the maximum velocity of the initial influx of P-32 -phosphate. (iii) The capacity of the wild type,to adapt within a few minutes to a transitory increase in the external phosphate concentrati on in an energetically efficient way (G. Falkner et al. 1994, C R Acad Sci Paris, Life sciences 317: 535-541) is lost in the mutant. As a re sult, the mutant can no longer attain pulse-adapted states that reflec t in a characteristic way preceding exposures to higher phosphate conc entrations.