A simple and highly efficient fixation method for Chrysochromulina polylepis (Prymnesiophytes) for analytical flow cytometry

Background: To study the fragile Prymnesiophyte species Chrysochromulina po lylepis by flow cytometry (FC), we needed an effective fixation method. Thi s method must guarantee a high yield of fixed cells to achieve acceptable m easurement times by FC and to allow quick processing of many samples. Moreo ver, we wanted a method that allows for storage of fixed samples when FC an alysis cannot be done immediately. Methods: Different aldehydes and methanol were tested at different final co ncentrations. Gravity sedimentation and centrifugation were applied to achi eve higher cell concentrations. Storage of fixed samples was tested under d ifferent conditions. Results: 0.25% glutaraldehyde (GA) fixation yielded a recovery rate of abou t 90%. The signals obtained by FC analysis were excellent. It is possible t o centrifuge GA-fixed cells and to store them for several weeks. Conclusions: GA is the fixative of choice for FC analysis of C. polylepis ( and possibly other small delicate species) because it yielded highly signif icant recovery rates and high-quality FC signals. Cells call be centrifuged re, increase the cell concentration, thereby achieving short measurement t imes with FC. The possibility of long-term storage of fixed cells presents an additional advantage if FC analysis cannot be done immediately. Cytometr y 44: 126-132, 2001. (C) 2001 Wiley-Liss, Inc.