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Effects of fixation and storage on flow cytometric analysis of marine bacteria |
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| Authors: | Eriko Kamiya Shinji Izumiyama Masahiko Nishimura James G Mitchell Kazuhiro Kogure |
| Institution: | (1) Marine Microbiology Division, Ocean Research Institute, The University of Tokyo, Minamidai, Nakano-ku, Tokyo 164-8639, Japan;(2) Ikeda Scientific Co., LTD., Kanda-KS Bldg., Kaji-cho, Chiyoda-ku, Tokyo 101-0044, Japan;(3) Present address: Department of Parasitology, National Institute of Infectious Diseases, Toyama, Shinjuku-ku, Tokyo 162-8640, Japan;(4) Present address: Biological Sciences, Flinders University, P.O. Box 2100, Adelaide, SA, 5001, Australia |
| Abstract: | Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria. Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered. |
| Keywords: | Flow cytometry marine bacteria fixation storage HDNA bacteria LDNA bacteria |
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