156
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
The monograph by Professor S. Kuznetsov, published as long ago as 1952
(Kuznetsov 1952), also contained evaluations of the density of bacterioplankton in lakes, which were quite sound from the state-of-the-art knowledge.
Curiously, these achievements found no recognition outside Russia. After
numerous Russian publications on the number of biomass and production
of bacteria in the sea and in freshwater, as well as manuals published in
1972-1974 (Sorokin and Kadota 1972; Romanenko and Kuznetsov 1974) statements like: "Until recently, methods allowing determination of abundance and
production rates of marine bacteria have not been available" (Douglas et al.
1987) were the norm. "Until recently" in this statement means: until the
appearance in 1974 of the epifluorescence method for direct microscopic
count of bacteria developed by Daley and Hobbie (1975) and Hobbie et al.
(1977).
This new method revealed itself to be foolproof. It made it possible to
see even the smallest bacterial cells of 0.4-0.6 M-m in size, which were missed
most often on the membrane filters. Therefore Russian data on the density of
bacterioplankton, obtained by membrane filter counting, underestimated its
numerical abundance by approximately 1.5 times; but since the minor size fraction of bacterioplankton actually has also a minor share in its whole biomass,
the values of the latter presented in the above-mentioned Russian works are
quite comparable with its modern evaluations in various aquatic habitats. In
Table 4.1 a generalized range of the indices of microbial density in water and
in bottom sediments are given, as depending on the trophical level of water
basins.
4.2 Estimation of Relative Microbial Activity
in Aquatic Habitats
4.2.1 General Remarks
As mentioned above, with the use of radioisotopic methodology it is possible
to determine relative rates of various kinds of microbial activity in aquatic
environments and measure their absolute rates as well; but researchers are
often inclined to combine these different goals, which need a different methodological approach. This results in misunderstandings. The main difference
between these two approaches is not only that in one case the data are represented by comparative values, and in the other by absolute ones; the very
conditions of experiments in both cases are different. When estimating relative rates, it is not obligatory to simulate the in situ conditions concerning
oxygen content or substrate concentration (Griffiths et al. 1977). The main
stipulation is to make them uniform in all the series of samples so that the differences in the bacterial uptake rates or CO2 release reflect only a relative
quantity of active microbial cells per volume (or per total number of
Use of Radioisotopic Methodology in Aquatic Microbial Ecology
The monograph by Professor S. Kuznetsov, published as long ago as 1952
(Kuznetsov 1952), also contained evaluations of the density of bacterioplankton in lakes, which were quite sound from the state-of-the-art knowledge.
Curiously, these achievements found no recognition outside Russia. After
numerous Russian publications on the number of biomass and production
of bacteria in the sea and in freshwater, as well as manuals published in
1972-1974 (Sorokin and Kadota 1972; Romanenko and Kuznetsov 1974) statements like: "Until recently, methods allowing determination of abundance and
production rates of marine bacteria have not been available" (Douglas et al.
1987) were the norm. "Until recently" in this statement means: until the
appearance in 1974 of the epifluorescence method for direct microscopic
count of bacteria developed by Daley and Hobbie (1975) and Hobbie et al.
(1977).
This new method revealed itself to be foolproof. It made it possible to
see even the smallest bacterial cells of 0.4-0.6 M-m in size, which were missed
most often on the membrane filters. Therefore Russian data on the density of
bacterioplankton, obtained by membrane filter counting, underestimated its
numerical abundance by approximately 1.5 times; but since the minor size fraction of bacterioplankton actually has also a minor share in its whole biomass,
the values of the latter presented in the above-mentioned Russian works are
quite comparable with its modern evaluations in various aquatic habitats. In
Table 4.1 a generalized range of the indices of microbial density in water and
in bottom sediments are given, as depending on the trophical level of water
basins.
4.2 Estimation of Relative Microbial Activity
in Aquatic Habitats
4.2.1 General Remarks
As mentioned above, with the use of radioisotopic methodology it is possible
to determine relative rates of various kinds of microbial activity in aquatic
environments and measure their absolute rates as well; but researchers are
often inclined to combine these different goals, which need a different methodological approach. This results in misunderstandings. The main difference
between these two approaches is not only that in one case the data are represented by comparative values, and in the other by absolute ones; the very
conditions of experiments in both cases are different. When estimating relative rates, it is not obligatory to simulate the in situ conditions concerning
oxygen content or substrate concentration (Griffiths et al. 1977). The main
stipulation is to make them uniform in all the series of samples so that the differences in the bacterial uptake rates or CO2 release reflect only a relative
quantity of active microbial cells per volume (or per total number of