Differential uptake of orthophosphate and organic phosphorus substrates by bacteria and algae in Lake Kinneret

The availability of six organic phosphorus substrates (OPS)to serve as sources of this nutrient for natural populationsof phytoplanktonic algae and bacteria was tested by measuringthe degree to which the organic substrates decreased uptakeof ³²P]orthophosphate (³²Pⁱ). When added to samples of LakeKinneret water, six organo-phosphorus compounds usually loweredthe amount of ³²P_i] taken up by microplankton retained on 0.2-µfilters.In contrast, OPS addition generally stimulated ³²P_i uptake intothe mainly algal fraction (>3 µm), indicating thatthe bacteria were mostly responsible for utilising OPS. Thesparing effect of OPS addition on ³²P₁ uptake was very fast,suggestingthat the micro-organisms possessed constitutive or rapidly inducedenzyme systems to exploit the OPS.The results of this studyindicate that a significant flux of phosphorus may pass viaDOP into microbiota, especially bacteria, in some aquatic systems.