Determination of Microbial Production
181
control the ambiental specific radioactivity of labeled phosphate added, and
thus to measure the real uptake values, unlike during the use of thymidine or
leucine methods, and (2) a high sensitivity in measuring 32P04 uptake rate. The
problem in practical use of this method is the separation of its bacterial and
algal uptake in water samples; but this had been actually solved before
(Sorokin 1985). Moreover, it was demonstrated that the ratio between them
is very stable in a definite kind of pelagic ecosystem. Thus, once estimated, it
can be used in a given basin during a given period of seasonal plankton succession. As a prospective method it needs further development in order to be
recommended as a standard procedure. Its basic features are discussed below
(see Sect. 4.4.4.1).
A further radioisotopic method for measuring microbial production is
based upon the use of labeled sulfate 35S0~- (Campbell and Baker 1968;
Jordan and Peterson 1978; Jordan and Likens 1980; Cuhel et al. 1982; Hansen
1984). Sulfate sulfur is assimilated by planktonic algae and by a part of bacterioplankton for synthesis of sulfur-containing amino acids, which then are
incorporated into the proteins. The weak points of this method are its nonspecific consumption by the bacterioplankton and algae, and variability in the
percentage of microbial cells, which are autotrophic in relation to their assimilatory sulfur metabolism. In seawater its application is complicated by a high
background of sulfate content. Small wonder, then, that this method did not
become one of choice in microbial productivity studies.
Among various ways of application of epifiuorescence microscopic counting of bacteria for estimating the microbial growth rate and production, a
special place belongs to the FDC (frequency of diving cells) method. It is based
on determination by microscopy of the percentage of the cells in natural
microbial population which are in the division stage. (Hagstrom et al. 1979;
Newell and Christian 1981). The dividing cells are recognized on the Nucleopore filters by the presence of fission invaginations on their walls. Thus, their
number and also the total number of planktonic bacteria are counted on the
same filter. It is easy to imagine the degree of competence in microscopy necessary to distinguish and record each case of division in tiny bacterial cells,
especially those having a coccoid form, which most often dominate the microbial populations. The use of this method is really a matter of personal ability,
which makes it scarcely applicable for routine hydrobiological work. Moreover, the basic stipulations for the validity of FDC method, that: (1) all cells
in the population are growing, and (2) the time of division is equal for all of
them, actually cannot be met in natural bacterioplankton populations. In
reality, a significant part of them not divide at all, and the starving microbial
cell may divide without increasing its mass (Fallon et al. 1983). This method
has found practical application mostly as a reference guide for calibration of
other methods such as the thymidine method (Tuomi 1997). This author used
electronic microscopy FDC counting, which largely facilitates recognition of
dividing cells, but, evidently, cannot be used for the routine measurements of
181
control the ambiental specific radioactivity of labeled phosphate added, and
thus to measure the real uptake values, unlike during the use of thymidine or
leucine methods, and (2) a high sensitivity in measuring 32P04 uptake rate. The
problem in practical use of this method is the separation of its bacterial and
algal uptake in water samples; but this had been actually solved before
(Sorokin 1985). Moreover, it was demonstrated that the ratio between them
is very stable in a definite kind of pelagic ecosystem. Thus, once estimated, it
can be used in a given basin during a given period of seasonal plankton succession. As a prospective method it needs further development in order to be
recommended as a standard procedure. Its basic features are discussed below
(see Sect. 4.4.4.1).
A further radioisotopic method for measuring microbial production is
based upon the use of labeled sulfate 35S0~- (Campbell and Baker 1968;
Jordan and Peterson 1978; Jordan and Likens 1980; Cuhel et al. 1982; Hansen
1984). Sulfate sulfur is assimilated by planktonic algae and by a part of bacterioplankton for synthesis of sulfur-containing amino acids, which then are
incorporated into the proteins. The weak points of this method are its nonspecific consumption by the bacterioplankton and algae, and variability in the
percentage of microbial cells, which are autotrophic in relation to their assimilatory sulfur metabolism. In seawater its application is complicated by a high
background of sulfate content. Small wonder, then, that this method did not
become one of choice in microbial productivity studies.
Among various ways of application of epifiuorescence microscopic counting of bacteria for estimating the microbial growth rate and production, a
special place belongs to the FDC (frequency of diving cells) method. It is based
on determination by microscopy of the percentage of the cells in natural
microbial population which are in the division stage. (Hagstrom et al. 1979;
Newell and Christian 1981). The dividing cells are recognized on the Nucleopore filters by the presence of fission invaginations on their walls. Thus, their
number and also the total number of planktonic bacteria are counted on the
same filter. It is easy to imagine the degree of competence in microscopy necessary to distinguish and record each case of division in tiny bacterial cells,
especially those having a coccoid form, which most often dominate the microbial populations. The use of this method is really a matter of personal ability,
which makes it scarcely applicable for routine hydrobiological work. Moreover, the basic stipulations for the validity of FDC method, that: (1) all cells
in the population are growing, and (2) the time of division is equal for all of
them, actually cannot be met in natural bacterioplankton populations. In
reality, a significant part of them not divide at all, and the starving microbial
cell may divide without increasing its mass (Fallon et al. 1983). This method
has found practical application mostly as a reference guide for calibration of
other methods such as the thymidine method (Tuomi 1997). This author used
electronic microscopy FDC counting, which largely facilitates recognition of
dividing cells, but, evidently, cannot be used for the routine measurements of