Picoplankton measurement with flow cytometry: Protocol of fixation and preservation

The effects of fixation with paraformaldehyde or glutaraldehyde and preservation with liquid nitrogen on cell size, density, phycoerythrin fluorescence value (FL2) and chlorophyll fluorescence (FL3) of picoplanton cells were studied by using flow cytometry. The main conclusions are: 1) Liquid nitrogen environment is perfect for the preservation of fixed picoplankton sample and may reduce some cell loss of unfixed sample; 2) no significant effect of paraformaldehyde and glutaraldehyde fixation on picoplankton cell density; 3) paraformaldehyde and glutaraldehyde may reinforce the fluorescence strength, and glutaraldehyde is significant for FL2 and paraformaldehyde for FL3; and 4) this paper recommends that paraformaldehyde (final concentration of 0.8%-1.2%) or mixed fixative of 0.05% glutaraldehyde and paraformaldehyde (final concentration 0.8%-1.2%) are the common fixative for picoplankton.