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

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Abstract
The availability of six organic phosphorus substrates (OPS) to serve as sources of this nutrient for natural populations of phytoplanktonic algae and bacteria was tested by measuring the degree to which the organic substrates decreased uptake of [32P]orthophosphate (32Pi). When added to samples of Lake Kinneret water, six organo-phosphorus compounds usually lowered the amount of 32Pi] taken up by microplankton retained on 0.2-μfilters. In contrast, OPS addition generally stimulated 32Pi uptake into the mainly algal fraction (>3 μm), indicating that the bacteria were mostly responsible for utilising OPS. The sparing effect of OPS addition on 32P1 uptake was very fast,suggesting that the micro-organisms possessed constitutive or rapidly induced enzyme systems to exploit the OPS.The results of this study indicate that a significant flux of phosphorus may pass via DOP into microbiota, especially bacteria, in some aquatic systems.

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