Determination of Microbial Production
197
This method is applicable for vertical profiling of water column in stratified
basins with redox zones and hypolimnetic oxygen minima as well for transections in zones of hydrothermal activity. Two series of samples are taken in this
case: one to estimate the values of total dark CO2 uptake by bacterioplankton
(Ac) and the second for the estimation of the relative activity of heterotrophic
microbial populations (Ha) with the aid of 14C-labeled protein hydrolyzate (see
Sect. 4.2.3.2). One site of sampling in this series should be taken in the layer
where any possibility of chemosynthetic CO2 uptake is practically absent (the
reference samples). It can be, respectively, the surface layer of water columns
or an area distant from the zone of hydrothermal influence. After all the measurements are made and Ac-values calculated, the heterotrophic dark uptake
A xRh ·
3
1
(Ach) is determined as follows: ACh = c~ I , mgCm-- day- , where ACT is
hr
the dark CO2 uptake measured in the reference sample, mg Cm- 3 day-I, Rh is
the radioactivity of the 14C-portion hydrolyzate, incorporated by bacterioplankton in the reference sample, incubated, and processed in the same way
as the whole sample series (cpm), and Rhi is the same radioactivity measured
in the sample, in which a given Ach value is calculated. The CO2 uptake by
chemoautotrophic and methanotrophic microflora (Aca) is calculated as the
difference between its total dark uptake (Ac) and its calculated potential
uptake by the heterotrophic part of their microbial community (Ach): Aca = Ac
- A ch . Then the total bacterial production Ph can be calculated as described
above under (1).
4.4.2.4 Determination of Anoxygenic Bacterial Photosynthesis
The general procedure to estimate the rate of anoxic bacterial photosynthesis
in situ in water columns or in upper layers of bottom sediments remains, in
principle, the same as described above for measuring the primary photosynthetic production of phytoplankton (see Sect. 2.3.2.5) or microphytobenthos
(see Sect. 2.5.4). There are differences in the sampling and incubation procedures. To ensure accurate measurement of the production by anaerobic
photosynthetic bacteria, the protocol of experiments takes the following stipulations into account: (1) careful preservation of the in situ redox conditions
in the experimental bottles or sediment cores, not permitting their contact with
air, and (2) incubation of samples in situ with ambient illumination, preventing the exposure of samples to direct sunlight. The precautions during water
sampling for this analysis are the same as for sampling during estimation of
chemosynthesis (see above). The light samples of 250-300 m 3 capacity are filled
with water sampled one hour before dawn from six to eight depths on the vertical profile within the redox zone down to depth, where the illumination is
-0.05% PAR. Each sample is distributed into two 300-cm3 bottles. One serves
197
This method is applicable for vertical profiling of water column in stratified
basins with redox zones and hypolimnetic oxygen minima as well for transections in zones of hydrothermal activity. Two series of samples are taken in this
case: one to estimate the values of total dark CO2 uptake by bacterioplankton
(Ac) and the second for the estimation of the relative activity of heterotrophic
microbial populations (Ha) with the aid of 14C-labeled protein hydrolyzate (see
Sect. 4.2.3.2). One site of sampling in this series should be taken in the layer
where any possibility of chemosynthetic CO2 uptake is practically absent (the
reference samples). It can be, respectively, the surface layer of water columns
or an area distant from the zone of hydrothermal influence. After all the measurements are made and Ac-values calculated, the heterotrophic dark uptake
A xRh ·
3
1
(Ach) is determined as follows: ACh = c~ I , mgCm-- day- , where ACT is
hr
the dark CO2 uptake measured in the reference sample, mg Cm- 3 day-I, Rh is
the radioactivity of the 14C-portion hydrolyzate, incorporated by bacterioplankton in the reference sample, incubated, and processed in the same way
as the whole sample series (cpm), and Rhi is the same radioactivity measured
in the sample, in which a given Ach value is calculated. The CO2 uptake by
chemoautotrophic and methanotrophic microflora (Aca) is calculated as the
difference between its total dark uptake (Ac) and its calculated potential
uptake by the heterotrophic part of their microbial community (Ach): Aca = Ac
- A ch . Then the total bacterial production Ph can be calculated as described
above under (1).
4.4.2.4 Determination of Anoxygenic Bacterial Photosynthesis
The general procedure to estimate the rate of anoxic bacterial photosynthesis
in situ in water columns or in upper layers of bottom sediments remains, in
principle, the same as described above for measuring the primary photosynthetic production of phytoplankton (see Sect. 2.3.2.5) or microphytobenthos
(see Sect. 2.5.4). There are differences in the sampling and incubation procedures. To ensure accurate measurement of the production by anaerobic
photosynthetic bacteria, the protocol of experiments takes the following stipulations into account: (1) careful preservation of the in situ redox conditions
in the experimental bottles or sediment cores, not permitting their contact with
air, and (2) incubation of samples in situ with ambient illumination, preventing the exposure of samples to direct sunlight. The precautions during water
sampling for this analysis are the same as for sampling during estimation of
chemosynthesis (see above). The light samples of 250-300 m 3 capacity are filled
with water sampled one hour before dawn from six to eight depths on the vertical profile within the redox zone down to depth, where the illumination is
-0.05% PAR. Each sample is distributed into two 300-cm3 bottles. One serves