60
Kf
•
50
•
40
•
30
20
•
•
10
•
•
•
0
M
A
M
• -1
•
J
Determination of Microbial Production
209
•
•
J
•
•
•
A
•
•
s
»-----
•
•
o Months
Fig.4.13. The seasonal variability of empirical conversion factor K j (1) for calculation
of bacterioplankton production after measured TDR uptake in Lake Michigan, and (2)
its theoretical level. (After Scavia et al. 1987)
large shifts during the calculations of their volume-biomass. Therefore there
is good reason to have a reference method for calibration of the thymidine
method, which estimates production of bacteria directly in carbon units.
This method is the dark 14C02 uptake method (see above). The microscopy
methods employed for this purpose were reviewed by Ducklow and Carlson
(1992), Ducklow et al. (1992), Robarts and Zohary (1993), and Tuomi (1997).
They measured the production of microbial cells or their specific growth rates
in batch cultures, which may be translated into biomass units only after their
cell number and mean cell volume have been estimated. These methods
can be of subjective (especially the FDC method); but the batch cultures can
scarcely give realistic estimates of specific growth rates of natural bacterioplankton popUlations. The measurements in these cultures need at least
15-20 h of incubation, during which the bacterioplankton in them completely
change. The pre filtration procedure itself results in enrichment of the filtrate
used for preparation of batch cultures with the organic matter, and thus
accelerates the bacterial growth. This approach requires great expertise in
microscopy and is time-consuming, besides having some major drawbacks,
such as the change in natural microbial assemblages during experimental
manipulations or the introduction of metabolic inhibitors (Ferguson et al.
1984; Coveney and Wetzel 1988). The idea of using CH)-leucin to estimate the
conversion factor for the thymidine method (Bell 1990) seems to be unrealistic, because the leucin method itself still is not estalished and itself needs
calibration. Its use as reference for calibration (see above) of the thymidine
method would create the curious situation of the blind leading the blind. I rec-
Kf
•
50
•
40
•
30
20
•
•
10
•
•
•
0
M
A
M
• -1
•
J
Determination of Microbial Production
209
•
•
J
•
•
•
A
•
•
s
»-----
•
•
o Months
Fig.4.13. The seasonal variability of empirical conversion factor K j (1) for calculation
of bacterioplankton production after measured TDR uptake in Lake Michigan, and (2)
its theoretical level. (After Scavia et al. 1987)
large shifts during the calculations of their volume-biomass. Therefore there
is good reason to have a reference method for calibration of the thymidine
method, which estimates production of bacteria directly in carbon units.
This method is the dark 14C02 uptake method (see above). The microscopy
methods employed for this purpose were reviewed by Ducklow and Carlson
(1992), Ducklow et al. (1992), Robarts and Zohary (1993), and Tuomi (1997).
They measured the production of microbial cells or their specific growth rates
in batch cultures, which may be translated into biomass units only after their
cell number and mean cell volume have been estimated. These methods
can be of subjective (especially the FDC method); but the batch cultures can
scarcely give realistic estimates of specific growth rates of natural bacterioplankton popUlations. The measurements in these cultures need at least
15-20 h of incubation, during which the bacterioplankton in them completely
change. The pre filtration procedure itself results in enrichment of the filtrate
used for preparation of batch cultures with the organic matter, and thus
accelerates the bacterial growth. This approach requires great expertise in
microscopy and is time-consuming, besides having some major drawbacks,
such as the change in natural microbial assemblages during experimental
manipulations or the introduction of metabolic inhibitors (Ferguson et al.
1984; Coveney and Wetzel 1988). The idea of using CH)-leucin to estimate the
conversion factor for the thymidine method (Bell 1990) seems to be unrealistic, because the leucin method itself still is not estalished and itself needs
calibration. Its use as reference for calibration (see above) of the thymidine
method would create the curious situation of the blind leading the blind. I rec-