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In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted. The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and > 100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host-cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes.

There is controversy in the literature regarding the effects of plasmin on human platelets. We have studied the effects of plasmin on platelet glycoproteins, aggregation, shape change and secretion and found them to be dependent on experimental conditions: (a) Plasmin's effects on human platelets are only seen in gel-filtered platelets (GFP), presumably because in platelet rich plasma plasmin is bound to a2-antiplasmin; (b) in GFP to which fibrinogen has been added, platelet function remains intact; and (c) in the absence of fibrinogen, the effect of plasmin on GFP depends on whether stirring is performed or not. With stirring, platelets undergo shape change, secretion and aggregation in response to added plasmin. Aggregation is much stronger when CaCl(z) 1 mM is added. Without stirring, preincubation of GFP with plasmin leads to inhibition of platelet aggregation induced by subsequent platelet stimuli (thrombin, collagen, ristocetin or U46619). We have demonstrated that plasmin is a true platelet activating agent, in the sense that it induces platelet shape change and secretion. Plasmin will induce aggregation when added to stirred GFP. This may be because stirring protects glycoprotein (GP) IIbIIIa bound fibrinogen from being degradated by plasmin. When added to unstirred GFP, GP IIbIIIa bound fibrinogen may be readily accessible to degradation by plasmin, which may then behave like a platelet inhibitor.