Determination of Microbial Production
185
In order to understand the nature of dark 14C02 assimilation by natural
heterotrophic microbial populations, I estimated the degree of external incorporation into the cells of bacteria with different types of metabolism. This was
done by comparing the specific radioactivity ofTC02 in the medium (accounting for its dilution during bacterial growth) and in the biomass carbon of bacteria thus grown. The range of the shares of exogenous in the biomass of
various bacteria proved to be very wide (Table 4.4). In ordinary heterotrophic
bacteria growing on glucose as a single organic substrate, this percentage is
between 6 and 8%. Bacteria oxidizing the lower hydrocarbons like ethane,
heptane, or butane assimilate the same 7-8% from exogenous CO2, the
propane-oxidizing bacteria up to 13-14%. The methane and methanoloxidizing bacteria utilized 30 to 40% of COz-carbon, the same as sulfatereducing bacteria grown on lactate, ethanol, formate, or Hz-gas + acetate
(30-37%). The ability of methylotrophs growing on methane or methanol to
assimilate up to 70% of exogenous CO was confirmed by Malashenko et al.
(1978). The above formate-oxidizing bacterium, same like the true chemoautotrophic bacterium Hydrogenomonas flava Hz-gas as the single energy source,
extracted about 100% of the necessary carbon from external CO2. The share
of exogenous CO2 in the biomass produced by mixed populations of bacteria
isolated from the Rybinsk reservoir and grown on glucose, was about the
same as in cultures (6 to 8%). When grown on glucose with the addition of
20 mg 1-1 peptone, the same mixed popUlation of bacteria utilized only 2-3%
of the external CO2. About the same percentage of the use of external CO2
by bacteria grown on glucose (6-7%) was recorded by Overbeck (1984).
In order to estimate the share of COz-carbon in biomass produced by
natural bacterioplankton in water reservoirs, Romanenko (1963) used the
ratio between its production, determined by the direct microscopy method of
Ivanov (1955), and the values of CO2 dark uptake, both expressed in carbon
units. The results of numerous measurements convinced him that this ratio,
being close to 6%, was rather stable in the upper water layer during the
summer period. These data enabled the development of the radiocarbon
method for estimating bacterial production based on measuring of dark 14C02
uptake (Romanenko 1964). At the same time, ways to distinguish heterotrophic and chemoautotrophic dark uptake of CO2 were found (Sorokin
1955a; 1964b; 1965; Romanenko 1964), which opened the way for the practical use of this method of assessing microbial production in various bodies of
water in the water column and also in bottom sediments. In Russia, it soon
became the main procedure for such estimations. The results have been
reviewed by Sorokin (1965,1974, 1981c), Kuznetsov (1970), and Romanenko
(1985). During its long use, it was compared many times with other methods
(Overbeck and Daley 1973; Overbeck 1979, 1984; Li 1982,1984; Bell et al.1983;
Kuparinen 1985; Saralov 1988), and as a result, its technique was correspondingly corrected and improved (Sorokin 1990b). At present, this method can be
used as a reference methodology for calibration of other methods which need
such a procedure, such as the TDR method.
185
In order to understand the nature of dark 14C02 assimilation by natural
heterotrophic microbial populations, I estimated the degree of external incorporation into the cells of bacteria with different types of metabolism. This was
done by comparing the specific radioactivity ofTC02 in the medium (accounting for its dilution during bacterial growth) and in the biomass carbon of bacteria thus grown. The range of the shares of exogenous in the biomass of
various bacteria proved to be very wide (Table 4.4). In ordinary heterotrophic
bacteria growing on glucose as a single organic substrate, this percentage is
between 6 and 8%. Bacteria oxidizing the lower hydrocarbons like ethane,
heptane, or butane assimilate the same 7-8% from exogenous CO2, the
propane-oxidizing bacteria up to 13-14%. The methane and methanoloxidizing bacteria utilized 30 to 40% of COz-carbon, the same as sulfatereducing bacteria grown on lactate, ethanol, formate, or Hz-gas + acetate
(30-37%). The ability of methylotrophs growing on methane or methanol to
assimilate up to 70% of exogenous CO was confirmed by Malashenko et al.
(1978). The above formate-oxidizing bacterium, same like the true chemoautotrophic bacterium Hydrogenomonas flava Hz-gas as the single energy source,
extracted about 100% of the necessary carbon from external CO2. The share
of exogenous CO2 in the biomass produced by mixed populations of bacteria
isolated from the Rybinsk reservoir and grown on glucose, was about the
same as in cultures (6 to 8%). When grown on glucose with the addition of
20 mg 1-1 peptone, the same mixed popUlation of bacteria utilized only 2-3%
of the external CO2. About the same percentage of the use of external CO2
by bacteria grown on glucose (6-7%) was recorded by Overbeck (1984).
In order to estimate the share of COz-carbon in biomass produced by
natural bacterioplankton in water reservoirs, Romanenko (1963) used the
ratio between its production, determined by the direct microscopy method of
Ivanov (1955), and the values of CO2 dark uptake, both expressed in carbon
units. The results of numerous measurements convinced him that this ratio,
being close to 6%, was rather stable in the upper water layer during the
summer period. These data enabled the development of the radiocarbon
method for estimating bacterial production based on measuring of dark 14C02
uptake (Romanenko 1964). At the same time, ways to distinguish heterotrophic and chemoautotrophic dark uptake of CO2 were found (Sorokin
1955a; 1964b; 1965; Romanenko 1964), which opened the way for the practical use of this method of assessing microbial production in various bodies of
water in the water column and also in bottom sediments. In Russia, it soon
became the main procedure for such estimations. The results have been
reviewed by Sorokin (1965,1974, 1981c), Kuznetsov (1970), and Romanenko
(1985). During its long use, it was compared many times with other methods
(Overbeck and Daley 1973; Overbeck 1979, 1984; Li 1982,1984; Bell et al.1983;
Kuparinen 1985; Saralov 1988), and as a result, its technique was correspondingly corrected and improved (Sorokin 1990b). At present, this method can be
used as a reference methodology for calibration of other methods which need
such a procedure, such as the TDR method.