Decomposition: Relative Bacterial Heterotrophic Activity
277
device (Exercise 12). Place the water samples into clean t -liter bottles, remove about 100 ml of
sediment slurry from the upper first centimeter of the sediments, and place into a clean
container. Place all of the samples in an ice chest and transport to the laboratory as rapidly as
possible, after measuring the water temperatures at the points of collection.
2. Determine the relative assimilation-mineralization rates of an organic substrate (e.g., glucose
or acetate) by the bacteria of the water samples using the procedures outlined. Determine the
mineralization rate of the same substrate using a lO-ml slurry of sediments with a IS-min
incubation period. Incubate at temperatures as close to the environmental conditions as
possible.
3. Calculate the rates of substrate utilization and mineralization as outlined and compare the
results between the planktonic and sediment communities.
4. Answer the questions following Option 6.
OPTION 6. LABORATORY ANALYSES
1. Using water samples provided by the instructor, determine the relative bacterial assimilation
and mineralization rates of one or more organic substrates (e.g., glucose, acetate, or amino
acid) by the procedures outlined. Incubate at a constant temperature or incubate replicates
at high (e.g., 25 D C) and low (lODC) temperatures.
2. Calculate the assimilation-mineralization parameters as outlined and compare observed
differences in heterotrophic activities.
3. Answer the following questions.
Questions
1. Kinetic analyses of heterotrophic activity assume that active transport is the rate-limiting
step in the metabolism of the substrate and that the transport system is in steady-state
equilibrium. Do you believe these assumptions are met in applying the method to natural
communities? If not, how would the results be affected?
2. If the incorporated substrate does not remain in the cells or is liberated as some gas other
than CO2, how would the results be affected? Would it be possible to measure labeled
substrates that were metabolized and released in soluble form?
3. The kinetic method assumes that there was an insignificant change in the size of the
populations comprising the bacterial community during the incubation. Do you believe that
this assumption is valid? Explain. Do you believe that the uptake rates measured over the
incubation period estimate accurately the instantaneous initial uptake velocities? Why?
4. When your data do not follow a hyperbolic relationship where uptake velocity approaches a
saturation level with increasing substrate concentrations, what do you think was happening?
[See Wright (1973).]
5. The kinetic method further assumes that various bacteria in a sample of water have similar
enzymatic transport constants (K,) for the substrate being assayed. Do you believe that this
assumption is valid? [See Hobbie and Wright (1965).]
6. What does the turnover time (T,) value for a naturally occurring substrate mean? How might
T, be useful in comparing different lakes or as an index of eutrophication of lakes? [See
Hobbie and Crawford (1969b) and Wetzel (1983).]
7. The kinetic method as presented here can analyze the utilization activity of only one simple
organic compound at a time. What about the myriad of other dissolved organic substrates
that occur in natural waters that are being decomposed at varying rates? How might the
utilization rates of these compounds be determined as well? Several substrates
simultaneously?
8. How might this kinetic approach be applied to the bacterial populations utilizing organic
substrates in the interstitial water of sediments? [See Harrison et aI., (1971) and Meyer-Reil
(1978).] Would it be possible to evaluate the amount of substrate assimilated in microbial
biomass in a sediment system? What problems would be encountered?
277
device (Exercise 12). Place the water samples into clean t -liter bottles, remove about 100 ml of
sediment slurry from the upper first centimeter of the sediments, and place into a clean
container. Place all of the samples in an ice chest and transport to the laboratory as rapidly as
possible, after measuring the water temperatures at the points of collection.
2. Determine the relative assimilation-mineralization rates of an organic substrate (e.g., glucose
or acetate) by the bacteria of the water samples using the procedures outlined. Determine the
mineralization rate of the same substrate using a lO-ml slurry of sediments with a IS-min
incubation period. Incubate at temperatures as close to the environmental conditions as
possible.
3. Calculate the rates of substrate utilization and mineralization as outlined and compare the
results between the planktonic and sediment communities.
4. Answer the questions following Option 6.
OPTION 6. LABORATORY ANALYSES
1. Using water samples provided by the instructor, determine the relative bacterial assimilation
and mineralization rates of one or more organic substrates (e.g., glucose, acetate, or amino
acid) by the procedures outlined. Incubate at a constant temperature or incubate replicates
at high (e.g., 25 D C) and low (lODC) temperatures.
2. Calculate the assimilation-mineralization parameters as outlined and compare observed
differences in heterotrophic activities.
3. Answer the following questions.
Questions
1. Kinetic analyses of heterotrophic activity assume that active transport is the rate-limiting
step in the metabolism of the substrate and that the transport system is in steady-state
equilibrium. Do you believe these assumptions are met in applying the method to natural
communities? If not, how would the results be affected?
2. If the incorporated substrate does not remain in the cells or is liberated as some gas other
than CO2, how would the results be affected? Would it be possible to measure labeled
substrates that were metabolized and released in soluble form?
3. The kinetic method assumes that there was an insignificant change in the size of the
populations comprising the bacterial community during the incubation. Do you believe that
this assumption is valid? Explain. Do you believe that the uptake rates measured over the
incubation period estimate accurately the instantaneous initial uptake velocities? Why?
4. When your data do not follow a hyperbolic relationship where uptake velocity approaches a
saturation level with increasing substrate concentrations, what do you think was happening?
[See Wright (1973).]
5. The kinetic method further assumes that various bacteria in a sample of water have similar
enzymatic transport constants (K,) for the substrate being assayed. Do you believe that this
assumption is valid? [See Hobbie and Wright (1965).]
6. What does the turnover time (T,) value for a naturally occurring substrate mean? How might
T, be useful in comparing different lakes or as an index of eutrophication of lakes? [See
Hobbie and Crawford (1969b) and Wetzel (1983).]
7. The kinetic method as presented here can analyze the utilization activity of only one simple
organic compound at a time. What about the myriad of other dissolved organic substrates
that occur in natural waters that are being decomposed at varying rates? How might the
utilization rates of these compounds be determined as well? Several substrates
simultaneously?
8. How might this kinetic approach be applied to the bacterial populations utilizing organic
substrates in the interstitial water of sediments? [See Harrison et aI., (1971) and Meyer-Reil
(1978).] Would it be possible to evaluate the amount of substrate assimilated in microbial
biomass in a sediment system? What problems would be encountered?