Table 3. Comparison of PolyP Quantification Methods for Planktonic Samples.

method	applicable samples	summary of pros, cons, and recommendations
DAPI fluorescence22	all samples, cultured and environmental, freshwater and marine	pros: sensitive, easy operation, has been commonly used in environmental samples
		cons: high risk of overestimation due to interferences
		recommendations: should not be used as the sole method for polyP quantification
PPX digestion27	only freshwater cultures	pros: has been commonly used for various model unicellular organisms.
		cons: the activity of the enzyme in samples can be difficult to control and inhibitory molecules may cause interference, not working in marine plankton cultures and environmental samples
		recommendations: not recommended for environmental samples and marine cultures, unless other methods are also used to validate the results
JC-D7 fluorescence (this study)	all samples, cultured and environmental, freshwater and marine	pros: sensitive, easy operation, stable, and can work in various extractants and buffers; polyP specific and has no nucleic acid interference
		cons: has not been widely used (the dye is newly found).
		recommendations: if lysing agents other than those recommended in this paper are used, the fluorescence response (linearity and detection limit) should be tested, especially for lysing reagents with high salt contents