Dear Gunnar What stain are you using? Stains like acridine orange used traditionally for enumeration of marine bacteria by epifluorescence microscopy are improper for flow cytometry. The best to use is SYBR Green (see our recent paper: 1997 Marie, D., Partensky, F, Jacquet S., Vaulot, D. Enumeration and cell cycle analysis of natural populations of marine picoplankton by flow cytometry using the nucleic acid stain SYBR Green I. Applied Environmental Microbiology 63: 186-193.) You should of course filter the sheath fluid through 0.2 umand use either filtered sea water (best to match the refractive indexes of the sheath and the sample) or Q water. Pn the FACsort we typically use Green PMT settings of 500 and get very little noise. Good luck. ______________________________________ Daniel VAULOT Station Biologique CNRS - INSU - UPMC BP 74 29682 Roscoff Cx FRANCE Ph: 33 2 98 29 23 34 Fax: 33 2 98 29 23 24 e-mail: vaulot@sb-roscoff.fr W3: http://www.sb-roscoff.fr (PhytoPlankton Group)
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