the difference between different DMSO concentrations by adding
growth medium (see Note 5). For example, for the sample with
10% (v/v) DMSO, add 2 mL culture, 0.3 mL DMSO, 0.7 mL of
growth medium, and the chosen concentration of NR.
9. Place a cuvette with 2 mL of fresh (diluted) culture sample into
spectrofluorometer. Add x μL of DMSO (+ additional growth
medium) and the chosen volume of NR to the sample, and
follow the fluorescence for 20–40 min (see Notes 7 and 9).
10. Repeat step 9 with the different DMSO concentrations (see
Note 13). Figure 1 shows the results of an optimization experiment with a fixed NR concentration and three different solvents on the NR staining of Phaeodactylum tricornutum. The
results show fluorescence values per total lipids determined by
GC [11].
Fig. 1 The effect of dimethyl sulfoxide (DMSO), ethylene glycol (EG), and glycerol on the NR staining of
Phaeodactylum tricornutum in exponential (Exp), early stationary (Stat 1), and late stationary (Stat 2) growth
phases. The NR fluorescence values are divided by the total lipid concentration in the culture (mg/L). 20% (v/v)
DMSO produced the highest and most stable signal [11]
58
Katariina Natunen