Alkaline phosphatase activities among populations of the colony-forming diazotrophic cyanobacterium Trichodesmium spp. (cyanobacteria) in the Red Sea

Alkaline phosphatase activities of the diazotrophic marine cyanobacterium T richodesmium were studied among natural populations in the northern Red Sea and in laboratory cultures of Trichodesmium sp, strain WH9601, Open-water tuft-shaped colonies of Trichodesmium showed high alkaline phosphatase acti vities with 2.4-11.7 mu mol p-nitrophenylphosphate (PNPP) hydrolyzed.mug ch l a(-1).h(-1), irrespective of date or origin of the sample. Coastal popula tions of the Trichodesmium tuft colonies had low alkaline phosphatase activ ities with 0.2-0.5 mu mol PNPP.mug chl a(-1).h(-1). An exception was the Tr ichodesmium fall maximum, when both tuft colonies and the plankton communit y (< 100 mum) had alkaline phosphatase activities of 0.6-7.4 mu mol PNPP.mu g chl a(-1).h(-1). Likewise, the more rare puff and bowtie colonies of Tric hodesmium spp. in coastal waters had elevated alkaline phosphatase activiti es (0.8-1.6 mu mol PNPP.mug chi a(-1).h(-1)) as compared with tuft colonies coinhabiting the same waters. Intact filaments of tuft-forming Trichodesmi um sp, strain WH9601 from phosphate-replete cultures had a base alkaline ph osphatase activity of 0.5 mu mol PNPP.mug chl a(-1)h(-1). This activity und erwent a 10-fold increase in phosphate-deplete cultures and in cultures sup plied with glycerophosphate as the sole P source. The elevated level of alk aline phosphatase activity was sustained in P-deplete cultures, but it decl ined in cultures with glycerophosphate, The decline is suggested to result from feedback repression of alkaline phosphatase synthesis by the phosphate generated in the glycerophosphate hydrolysis, The enhanced alkaline phosph atase activities of Trichodesmium spp, populations provide evidence that P stress is an important factor in the ecology of Trichodesmium in the northe rn Red Sea.