214
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
ning the space distribution of bacterial production rates in upper mixed layers,
the samples for such an intercalibration are taken at two or three reference
stations which reflect the range of ambiental conditions in the basin. If the
main goal of the survey is the estimation of bacterial production on vertical
profiles in a stratified basin, the samples of water for the intercalibration
should be collected in the middle of the epilimnion, in the thermocline layer,
and below the thermocline in the hypolimnion.
The samples are collected in 3-1 glass jars. From the jar the series of subsamples first is taken for direct measuring of bacterial production (Ph) using
the 14C02 dark uptake method, described above in detail (see Sect. 4.4.2.2).
For this purpose, three bottles are filled having a capacity sufficient for two
parallel filtrations. Two of them are placed in the dark for 30min and one
control is fixed with the Lugol solution. The remaining procedure is carried
out as described above. As a result, the production of bacterioplankton (Ph)
is measured as mgCl-lh- l .
After 14C dark incubation has been started, the experiment for the estimation of R; is prepared and then conducted as described above with four parallel experimental and two control filtrations. These experiments are repeated
twice during each one third of the selected 14C-dark uptake incubation period:
for example, if this incubation lasts for 12h, the incubations for the estimation
of R; should be performed at 4th and 8th hours of this period. For this purpose,
the remaining jar with the water sample (>1.51) is incubated in the dark in the
same place as the 14C02 dark uptake bottles at the in situ temperature. The
R;-incubations with CH)-TDR are performed using subsamples taken from
this jar. The remaining procedure is as described. The R; values thus measured
are expressed as cpm 1-1 h- I . Then the PhIR; is calculated and the conversion
factor KI> fJ,g C cpm- 1 1- 1 thus found is used for the calculation of bacterial production after the R; values measured at stations (cpm I-I h- 1 ): Ph = K J X R; x 24
x 10 3 mgCm- 3 day-I.
4.4.3.3 Measuring Bacterial Production in Bottom Sediments
The thymidine method was adapted also for measuring bacterial production
in bottom sediments (Moriarty and Pollard 1981, 1982; Fallon et al.1983; Finlay
et al. 1984; Moriarty 1986). Parallel estimations with the aid of FDC method
demonstrated that the latter produces values five to ten times higher. These
values were recognized as an unrealistically high, and the FDC method as
unreliable for estimating the empirical TDR conversion factor for bottom sediments. Therefore only the theoretical conversion factors, ranging according to
different authors between 0.2 and 2 x 10 9 cells nmol- 1 were used in numerous
publications dealing with measuring bacterial production in bottom sediments,
the authors choosing among them. Despite the indications about the possibility of nonspecific labeling and the catabolism of tritiated thymidine discovered
in water samples incubated with CH)-TDR (see above), which greatly invali-
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
ning the space distribution of bacterial production rates in upper mixed layers,
the samples for such an intercalibration are taken at two or three reference
stations which reflect the range of ambiental conditions in the basin. If the
main goal of the survey is the estimation of bacterial production on vertical
profiles in a stratified basin, the samples of water for the intercalibration
should be collected in the middle of the epilimnion, in the thermocline layer,
and below the thermocline in the hypolimnion.
The samples are collected in 3-1 glass jars. From the jar the series of subsamples first is taken for direct measuring of bacterial production (Ph) using
the 14C02 dark uptake method, described above in detail (see Sect. 4.4.2.2).
For this purpose, three bottles are filled having a capacity sufficient for two
parallel filtrations. Two of them are placed in the dark for 30min and one
control is fixed with the Lugol solution. The remaining procedure is carried
out as described above. As a result, the production of bacterioplankton (Ph)
is measured as mgCl-lh- l .
After 14C dark incubation has been started, the experiment for the estimation of R; is prepared and then conducted as described above with four parallel experimental and two control filtrations. These experiments are repeated
twice during each one third of the selected 14C-dark uptake incubation period:
for example, if this incubation lasts for 12h, the incubations for the estimation
of R; should be performed at 4th and 8th hours of this period. For this purpose,
the remaining jar with the water sample (>1.51) is incubated in the dark in the
same place as the 14C02 dark uptake bottles at the in situ temperature. The
R;-incubations with CH)-TDR are performed using subsamples taken from
this jar. The remaining procedure is as described. The R; values thus measured
are expressed as cpm 1-1 h- I . Then the PhIR; is calculated and the conversion
factor KI> fJ,g C cpm- 1 1- 1 thus found is used for the calculation of bacterial production after the R; values measured at stations (cpm I-I h- 1 ): Ph = K J X R; x 24
x 10 3 mgCm- 3 day-I.
4.4.3.3 Measuring Bacterial Production in Bottom Sediments
The thymidine method was adapted also for measuring bacterial production
in bottom sediments (Moriarty and Pollard 1981, 1982; Fallon et al.1983; Finlay
et al. 1984; Moriarty 1986). Parallel estimations with the aid of FDC method
demonstrated that the latter produces values five to ten times higher. These
values were recognized as an unrealistically high, and the FDC method as
unreliable for estimating the empirical TDR conversion factor for bottom sediments. Therefore only the theoretical conversion factors, ranging according to
different authors between 0.2 and 2 x 10 9 cells nmol- 1 were used in numerous
publications dealing with measuring bacterial production in bottom sediments,
the authors choosing among them. Despite the indications about the possibility of nonspecific labeling and the catabolism of tritiated thymidine discovered
in water samples incubated with CH)-TDR (see above), which greatly invali-