metazoans were of two types, namely, rotifers and aquatic oligochaetes. The
former included Philodina erythrophthalma and Lecane sp., and the latter was
Aeolosoma hemprichi. These protozoans and metazoans frequently appear in both
natural ecosystems, such as lakes, marshes, rivers, and seas, and in artificial
ecosystems, such as biofilms and activated sludge, and they are easily cultured
and accurately counted. These strains were isolated from water treatment facilities
and a polluted lake.
Three species of algae belonging to Chlorophyta, Chlorella sp., Scenedesmus
quadricauda, and Chlamydomonas monticola and four species of blue-green algae,
Tolypothrix sp., Oscillatoria agardhii, Anabaena flos-aquae, and Microcystis
viridis, were used as producers. The strains were sourced from the Microbial Culture
Collection Center of NIES in Tsukuba, Japan. These algal species are often observed
in lakes and ordinal ponds. Four species of bacteria were used as decomposers,
namely, Pseudomonas putida (gram-negative aerobic rod bacteria), Bacillus cereus
(gram-positive aerobic endospore-forming rod bacteria), Acinetobacter sp. (gramnegative rod bacteria), and a coryneform bacterium (gram-positive rod bacteria).
Mixed cultures of these bacteria were utilized.
Taub’s basal medium (200 mL) containing 100 mg/L of polypeptone was placed
in a cotton-plugged 300 mL volume Erlenmeyer flask and sterilized by an autoclave
at 1 atm and 121
C for approximately 20 min. A stock culture of each microorganism was added, and the flask was placed in a growth chamber at 25
C under cool
white fluorescent lighting for 12 h (2500 lux) and in the dark for 12 h, sequentially.
Cultivation was conducted under static conditions.
Certain species of protozoan predators were able to be established within the
system, but others were not. All species of metazoan predator were able to coexist,
and filter feeders, such as rotifers, and detritus feeders, such as oligochaete, were also
able to coexist. All species of blue-green algae (as producers) were able to establish
themselves, notwithstanding any other microorganisms. All species of chlorophytes
were able to be established, and the combination of and interaction between
chlorophytes and protozoans appeared to be of importance. All species of bacterial
decomposers were able to establish themselves, with none disappearing in any of the
microcosms. It was apparent that ecosystem stability did not always increase as a
function of species richness. From these results, the species composition of a standardized microcosm was determined as the combination of one species of protozoa,
Cyclidium glaucoma (Ciliata); three metazoan species, including two rotifers, Lecane
sp. and Philodina erythrophthalma, and one oligochaete, Aeolosoma hemprichi, as
predators (consumers); two species of chlorophytes, Chlorella sp. and Scenedesmus
quadricauda, and one species of blue-green algae, Tolypothrix sp., as producers; and
four species of bacteria, Pseudomonas putida, Bacillus cereus, Acinetobacter sp., and
a coryneform bacterium.
12
K. Murakami et al.
former included Philodina erythrophthalma and Lecane sp., and the latter was
Aeolosoma hemprichi. These protozoans and metazoans frequently appear in both
natural ecosystems, such as lakes, marshes, rivers, and seas, and in artificial
ecosystems, such as biofilms and activated sludge, and they are easily cultured
and accurately counted. These strains were isolated from water treatment facilities
and a polluted lake.
Three species of algae belonging to Chlorophyta, Chlorella sp., Scenedesmus
quadricauda, and Chlamydomonas monticola and four species of blue-green algae,
Tolypothrix sp., Oscillatoria agardhii, Anabaena flos-aquae, and Microcystis
viridis, were used as producers. The strains were sourced from the Microbial Culture
Collection Center of NIES in Tsukuba, Japan. These algal species are often observed
in lakes and ordinal ponds. Four species of bacteria were used as decomposers,
namely, Pseudomonas putida (gram-negative aerobic rod bacteria), Bacillus cereus
(gram-positive aerobic endospore-forming rod bacteria), Acinetobacter sp. (gramnegative rod bacteria), and a coryneform bacterium (gram-positive rod bacteria).
Mixed cultures of these bacteria were utilized.
Taub’s basal medium (200 mL) containing 100 mg/L of polypeptone was placed
in a cotton-plugged 300 mL volume Erlenmeyer flask and sterilized by an autoclave
at 1 atm and 121
C for approximately 20 min. A stock culture of each microorganism was added, and the flask was placed in a growth chamber at 25
C under cool
white fluorescent lighting for 12 h (2500 lux) and in the dark for 12 h, sequentially.
Cultivation was conducted under static conditions.
Certain species of protozoan predators were able to be established within the
system, but others were not. All species of metazoan predator were able to coexist,
and filter feeders, such as rotifers, and detritus feeders, such as oligochaete, were also
able to coexist. All species of blue-green algae (as producers) were able to establish
themselves, notwithstanding any other microorganisms. All species of chlorophytes
were able to be established, and the combination of and interaction between
chlorophytes and protozoans appeared to be of importance. All species of bacterial
decomposers were able to establish themselves, with none disappearing in any of the
microcosms. It was apparent that ecosystem stability did not always increase as a
function of species richness. From these results, the species composition of a standardized microcosm was determined as the combination of one species of protozoa,
Cyclidium glaucoma (Ciliata); three metazoan species, including two rotifers, Lecane
sp. and Philodina erythrophthalma, and one oligochaete, Aeolosoma hemprichi, as
predators (consumers); two species of chlorophytes, Chlorella sp. and Scenedesmus
quadricauda, and one species of blue-green algae, Tolypothrix sp., as producers; and
four species of bacteria, Pseudomonas putida, Bacillus cereus, Acinetobacter sp., and
a coryneform bacterium.
12
K. Murakami et al.