TABLE 1.

Effect of fixative and permeabilization on the intensities of DAPI-DNA fluorescence of recalcitrant organisms as determined by flow cytometry

Sample	Treatment		Low-fluorescence cluster intensitya	High-fluorescence cluster
	Fixative(s)	No. of days		Intensity	% of total population
M. thermoautotrophicum	Unfixed		83	385	1
M. thermoautotrophicum	CH2O	7	38	300	10
M. thermoautotrophicum	CH2O	50	60	185	35
M. thermoautotrophicum	CH2O and Triton X-100	50	Absent	425	100
Resurrection Bay	CH2O	63	49	62	49
Resurrection Bay	CH2O and Triton X-100	63	84	242	86

^aIntensity of fluorescence expressed as a linear channel number for cells in a distinct low-fluorescence (i.e., lightly stained) cluster having a dry mass similar to that of cells in a high-fluorescence cluster. Data were obtained from dot plots of DNA versus cell mass such as those shown in Fig. 7 for single species as shown in Fig. 8.