Limnetica 30

Polyphosphate (poly-P) is a phosphate storage compound widespread in prokaryotic and eukaryotic cells. Its quantification, however, is not yet well developed for sediment samples because of the difficulties associated with using a single extractant to extract a specific P compound without altering others. The present work uses an analytical procedure already developed to measure poly-P in algal cultures and later modified here for sediments to study poly-P in the sediment. The procedure uses the Ethylenediaminetetraacetic acid (EDTA) method for sequential P-fractionation. This approach ensures that the main inorganic phosphate compounds (i.e., Fe- and Ca-bound phosphate) are extracted prior to poly-P quantification. We applied this method to suspensions likely to contain biologically produced poly-P, such as laboratory cultures of Synechocystis PCC 6803 (Cyanobacteriaceae), Anabaena variabilis (Cyanobacteriaceae), and Chlorella sp. (Chlorophyceae) growing in a Penriched medium, and activated sludge. According to this procedure, the concentrations of poly-P in Synechocystis PCC 6803, Anabaena variabilis and Chlorella cultures were 15.4, 6.2 and 7.2 % of the sum of all P-fractions, respectively, whereas activated sludge showed a lower percentage (3.7 %). Known volumes of these suspensions and a commercially available synthetic poly-P standard (Trimetaphosphate) were added to natural sediment. The P-composition of each sample was then compared in duplicate to the corresponding control samples (sediment alone). Poly-P in all control sediment samples was extremely low (0-2 µg g⁻¹ d.w.). It increased in all sediment suspensions to which biological samples had been added. The increase was particularly noteworthy for Synechocystis (up to 220 µg g⁻¹ d.w. of poly-P). The recovery of poly-P in sediment samples to which Anabaena cultures had been added showed some deviation from a 1:1 expected:observed ratio, particularly when 2 ml of the culture were added (ratio of 0.79). However, the recovery improved to 1.12:1 when a larger volume was added (5 ml), probably owing to the inhomogeneous nature of the cyanobacteria culture. In contrast, the addition of 500 mg of trimetaphosphate to the control sediment did not significantly increase (p > 0.05) the percentage found for the observed poly-P fraction. Consequently, biologically produced poly-P can be associated with the fraction of poly-P extracted through use of this procedure.