Bacterial Growth and Productivity
265
EXERCISES
OPTION 1. FIELD ANALYSES
1. Collect water samples at regular intervals from the central depression of a lake or reservoir
with a clean Van Dorn or similar nonmetallic water sampler. Dispense into two replicate
experimental bottles and a blank bottle from each depth for the productivity analyses. Also
fill a small bottle for bacterial enumeration; preserve with glutaraldehyde (see "Apparatus
and Supplies," p. 268).
2. Perform the 3H-thymidine incorporation assay of bacterial productivity and/or the
measures of bacterial production of protein as detailed in this exercise with in situ incubations
at the depth from which the samples were collected.
3. If possible, collect other vertical series of water samples for comparison from (a) within a
littoral zone among dense stands of higher aquatic plants, and (b) in the open water near
the mouth of an inlet stream.
4. If possible, make comparative collections and analyses of bacteria and bacterial productivity
from vertical profiles in (a) a relatively unproductive oligotrophic lake; (b) a productive,
eutrophic lake or reservoir; (c) the open water of a bog; and (d) a stream at several points
along its drainage (e.g., in the central stream and in backwaters from downstream and upstream stations and directly below the outlet from a lake source to the stream). In stratified
waters, determine the temperature and dissolved oxygen profiles.
5. In the laboratory, determine the incorporation rates into nucleic acids or protein in order
to estimate the bacterial productivity. Estimate the biovolume of bacteria from different
depths and sites by microscopic examination.
6. Answer the questions following option 2.
OPTION 2. LABORATORY EXERCISES
1. Using water samples provided by your instructor, determine the bacterial productivity
by the thymidine incorporation method or by bacterial production of protein with
incubations in the laboratory.
2. With samples of natural bacterial communities provided by your instructor, determine the
biovolume of the bacteria by microscopic examination and enumeration.
3. Answer the following questions.
Questions
1. Numbers, biomass, and productivity of planktonic bacteria generally increase with increasing
photosynthetic productivity of the phytoplankton. Studies have indicated that often between
20 and 80% of the extracellular organic carbon released by phytoplankton is utilized rapidly
by planktonic bacteria [e.g., Coveney and Wetzel (1989)]. If 30 to 50% of the photosynthetic
productivity were released either extracellularly or during autolysis as dissolved organic
substrates, what would this release mean for higher trophic levels?
2. What is the common lower limit for the removal of bacteria through ingestion by c1adoceran
zooplankton? By rotifers? By protozoans?
3. What is meant by the 'microbial loop"? What effects would such a cycling among algae,
bacteria and protozoans/microflagellates have on nutrient cycling via mineralization? [See
Pomeroy (1974).]
4. If many of the algae and bacteria were not ingested by animals, what would become of them?
5. Carbon flux through planktonic bacteria is usually less than 50% of the net phytoplankton
production. Where is the rest of the phytoplanktonic production utilized or stored?
265
EXERCISES
OPTION 1. FIELD ANALYSES
1. Collect water samples at regular intervals from the central depression of a lake or reservoir
with a clean Van Dorn or similar nonmetallic water sampler. Dispense into two replicate
experimental bottles and a blank bottle from each depth for the productivity analyses. Also
fill a small bottle for bacterial enumeration; preserve with glutaraldehyde (see "Apparatus
and Supplies," p. 268).
2. Perform the 3H-thymidine incorporation assay of bacterial productivity and/or the
measures of bacterial production of protein as detailed in this exercise with in situ incubations
at the depth from which the samples were collected.
3. If possible, collect other vertical series of water samples for comparison from (a) within a
littoral zone among dense stands of higher aquatic plants, and (b) in the open water near
the mouth of an inlet stream.
4. If possible, make comparative collections and analyses of bacteria and bacterial productivity
from vertical profiles in (a) a relatively unproductive oligotrophic lake; (b) a productive,
eutrophic lake or reservoir; (c) the open water of a bog; and (d) a stream at several points
along its drainage (e.g., in the central stream and in backwaters from downstream and upstream stations and directly below the outlet from a lake source to the stream). In stratified
waters, determine the temperature and dissolved oxygen profiles.
5. In the laboratory, determine the incorporation rates into nucleic acids or protein in order
to estimate the bacterial productivity. Estimate the biovolume of bacteria from different
depths and sites by microscopic examination.
6. Answer the questions following option 2.
OPTION 2. LABORATORY EXERCISES
1. Using water samples provided by your instructor, determine the bacterial productivity
by the thymidine incorporation method or by bacterial production of protein with
incubations in the laboratory.
2. With samples of natural bacterial communities provided by your instructor, determine the
biovolume of the bacteria by microscopic examination and enumeration.
3. Answer the following questions.
Questions
1. Numbers, biomass, and productivity of planktonic bacteria generally increase with increasing
photosynthetic productivity of the phytoplankton. Studies have indicated that often between
20 and 80% of the extracellular organic carbon released by phytoplankton is utilized rapidly
by planktonic bacteria [e.g., Coveney and Wetzel (1989)]. If 30 to 50% of the photosynthetic
productivity were released either extracellularly or during autolysis as dissolved organic
substrates, what would this release mean for higher trophic levels?
2. What is the common lower limit for the removal of bacteria through ingestion by c1adoceran
zooplankton? By rotifers? By protozoans?
3. What is meant by the 'microbial loop"? What effects would such a cycling among algae,
bacteria and protozoans/microflagellates have on nutrient cycling via mineralization? [See
Pomeroy (1974).]
4. If many of the algae and bacteria were not ingested by animals, what would become of them?
5. Carbon flux through planktonic bacteria is usually less than 50% of the net phytoplankton
production. Where is the rest of the phytoplanktonic production utilized or stored?