Estimation of Relative Microbial Activity in Aquatic Habitats
167
3. Estimation of incubation time
The time course curve of uptake of the labeled organic substrate at its micromolar concentration by natural populations of bacterioplankton looks the
same as the time course of the growth of a microbial culture (Fig. 4.4). The
incubation should be haIted before the start of logarithmic growth phase at
the point of turn up of the curve, as shown in Fig. 4.4. Practically, it can be estimated in two ways, depending on the possibility of immediate measuring of
filter radioactivity. To determine this is possible: two to three parallel samples
are charged with isotopic solution and serve as signals within the series of
experimental samples. During the incubation of whole series, the subsamples
are taken every hour from these signal samples and filtered according to the
procedure described below. The results are plotted at the time course curve.
The whole experiment comes to an end when this curve starts to move
upwards.
Another way is the construction of the time course curves for a given basin
or research area by standard experimental procedure selected by researcher
for a given program of investigation of the heterotrophic potential. These
curves are usually rather stable. Then the standard exposure time is selected
for the whole sampling program of 1 h before the curves start to move
upwards.
4. The procedure: use of glutamate and protein hydrolyzate
The samples collected on vertical profiles or at the area cross sections are
stored in the refrigerator at a temperature of 2-4 °C for up to 8-10h during
continuing sampling. After the latter is finished all the samples are placed into
the incubator in which the temperature is adjusted to and kept at 18-20°C.
After the temperature of the water in the bottles is equalized at this level, the
Ri
6000
4000
2000
o~------~-----+------~------+-----~-o
2
4
6
10
Fig.4.4. Time-course curve of uptake rate of 14C - protein hydrolyzate in surface water
sample from the North Pacific incubated at 20°e. R; Radioactivity of bacterioplankton, Cpm 50ml- 1 ; t incubation time, h
167
3. Estimation of incubation time
The time course curve of uptake of the labeled organic substrate at its micromolar concentration by natural populations of bacterioplankton looks the
same as the time course of the growth of a microbial culture (Fig. 4.4). The
incubation should be haIted before the start of logarithmic growth phase at
the point of turn up of the curve, as shown in Fig. 4.4. Practically, it can be estimated in two ways, depending on the possibility of immediate measuring of
filter radioactivity. To determine this is possible: two to three parallel samples
are charged with isotopic solution and serve as signals within the series of
experimental samples. During the incubation of whole series, the subsamples
are taken every hour from these signal samples and filtered according to the
procedure described below. The results are plotted at the time course curve.
The whole experiment comes to an end when this curve starts to move
upwards.
Another way is the construction of the time course curves for a given basin
or research area by standard experimental procedure selected by researcher
for a given program of investigation of the heterotrophic potential. These
curves are usually rather stable. Then the standard exposure time is selected
for the whole sampling program of 1 h before the curves start to move
upwards.
4. The procedure: use of glutamate and protein hydrolyzate
The samples collected on vertical profiles or at the area cross sections are
stored in the refrigerator at a temperature of 2-4 °C for up to 8-10h during
continuing sampling. After the latter is finished all the samples are placed into
the incubator in which the temperature is adjusted to and kept at 18-20°C.
After the temperature of the water in the bottles is equalized at this level, the
Ri
6000
4000
2000
o~------~-----+------~------+-----~-o
2
4
6
10
Fig.4.4. Time-course curve of uptake rate of 14C - protein hydrolyzate in surface water
sample from the North Pacific incubated at 20°e. R; Radioactivity of bacterioplankton, Cpm 50ml- 1 ; t incubation time, h