natural ecosystems such as rivers, lakes, and marshes and in artificial ecosystems
including activated sludge and biofilms. Especially, interactions among microorganisms, such as prey-predator interactions, are significant (Sudo et al. 1990). Using a
microcosm system for the estimation of the proliferation and decay of GEMs is a
useful method, because the microcosm has very high reproducibility and reflects the
natural ecosystem.
7.13.1 Escherichia coli HB101/pBR325
Escherichia coli is one species of bacillus of gram-negative rods and is classified as
facultative anaerobic bacteria. These bacteria are one of the major species that are
present not only in the environment but also in the digestive tract of warm-blooded
animals (birds and mammals), especially humans. Their size is usually 0.4–0.7 μm
along the short axis and 2.0–4.0 μm along the long axis, but the long axis can be
shortened, and some cells are nearly spherical. It is a model organism representative of
bacteria, and it is used as a material in various studies, such as in genetic engineering,
and also for the production of chemical substances through gene incorporation. Here,
we focused on the competitive relationship among four taxa of bacteria, which are the
lowest organisms on the microcosmic food chain. Escherichia coli HB101/pBR325
was added at 1, 10, and 100 times the abundance of indigenous bacteria in the
microcosm, and its influence on the structure and function of the ecosystem was
examined. The pBR325, a 5.9-kbp-sized vector plasmid, which is widely used for
gene manipulation, is a non-transmissible plasmid, coding Cm
r
, Tc
r
, and Ap
r and
having Eco RI, Bam HI, Hind III, and Sal I sites on its nucleotide sequence.
Escherichia coli HB101/pBR325 rapidly decreased at 1-, 10-, or 100-times
inoculation concentrations in viable counts using the selective media method following microcosm inoculation, and the abundance of microorganisms (in particular,
its primary consumer, the protozoan ciliate Cyclidium glaucoma) in the microcosm
increased. Escherichia coli HB101/pBR325 has been shown to be a suitable food
source for constituent heterotrophic groups in the microcosm. By comparison, in
N 30 , no significant difference was observed between systems with Escherichia coli
added and systems without it (control system). Escherichia coli HB101/pBR325, as
GEMs, decreased in its abundance in the same manner as Bacillus thuringiensis. The
population density of Escherichia coli was 3.6 Â 10
7 CFU/mL on the injected day
(16th day) and rapidly decreased to 2.3 Â 10
5 CFU/mL 2 days after (18th day),
7.2 Â 10
3 CFU/mL 7 days after (23rd day), and 6.8 Â 10
3 CFU/mL 14 days after
(30th day). The predation effect of the protozoan Cyclidium glaucoma was observed
at the same time. This indicates that Escherichia coli HB101/pBR325 was a suitable
food source for the indigenous heterotrophs in the microcosm.
From an estimation of the succession pattern of microorganisms, Cyclidium
glaucoma was strongly influenced by Escherichia coli HB101/pBR325, especially
since this protozoan’s density increased compared to other taxa, such as rotifer
Philodina erythrophthalma, which slightly increased in abundance under these
conditions, and compared with the control microcosm. From an estimation of N 30
7 Example Assessments of the Microcosm N-System
139
including activated sludge and biofilms. Especially, interactions among microorganisms, such as prey-predator interactions, are significant (Sudo et al. 1990). Using a
microcosm system for the estimation of the proliferation and decay of GEMs is a
useful method, because the microcosm has very high reproducibility and reflects the
natural ecosystem.
7.13.1 Escherichia coli HB101/pBR325
Escherichia coli is one species of bacillus of gram-negative rods and is classified as
facultative anaerobic bacteria. These bacteria are one of the major species that are
present not only in the environment but also in the digestive tract of warm-blooded
animals (birds and mammals), especially humans. Their size is usually 0.4–0.7 μm
along the short axis and 2.0–4.0 μm along the long axis, but the long axis can be
shortened, and some cells are nearly spherical. It is a model organism representative of
bacteria, and it is used as a material in various studies, such as in genetic engineering,
and also for the production of chemical substances through gene incorporation. Here,
we focused on the competitive relationship among four taxa of bacteria, which are the
lowest organisms on the microcosmic food chain. Escherichia coli HB101/pBR325
was added at 1, 10, and 100 times the abundance of indigenous bacteria in the
microcosm, and its influence on the structure and function of the ecosystem was
examined. The pBR325, a 5.9-kbp-sized vector plasmid, which is widely used for
gene manipulation, is a non-transmissible plasmid, coding Cm
r
, Tc
r
, and Ap
r and
having Eco RI, Bam HI, Hind III, and Sal I sites on its nucleotide sequence.
Escherichia coli HB101/pBR325 rapidly decreased at 1-, 10-, or 100-times
inoculation concentrations in viable counts using the selective media method following microcosm inoculation, and the abundance of microorganisms (in particular,
its primary consumer, the protozoan ciliate Cyclidium glaucoma) in the microcosm
increased. Escherichia coli HB101/pBR325 has been shown to be a suitable food
source for constituent heterotrophic groups in the microcosm. By comparison, in
N 30 , no significant difference was observed between systems with Escherichia coli
added and systems without it (control system). Escherichia coli HB101/pBR325, as
GEMs, decreased in its abundance in the same manner as Bacillus thuringiensis. The
population density of Escherichia coli was 3.6 Â 10
7 CFU/mL on the injected day
(16th day) and rapidly decreased to 2.3 Â 10
5 CFU/mL 2 days after (18th day),
7.2 Â 10
3 CFU/mL 7 days after (23rd day), and 6.8 Â 10
3 CFU/mL 14 days after
(30th day). The predation effect of the protozoan Cyclidium glaucoma was observed
at the same time. This indicates that Escherichia coli HB101/pBR325 was a suitable
food source for the indigenous heterotrophs in the microcosm.
From an estimation of the succession pattern of microorganisms, Cyclidium
glaucoma was strongly influenced by Escherichia coli HB101/pBR325, especially
since this protozoan’s density increased compared to other taxa, such as rotifer
Philodina erythrophthalma, which slightly increased in abundance under these
conditions, and compared with the control microcosm. From an estimation of N 30
7 Example Assessments of the Microcosm N-System
139