Infusoria, which is a collective term that describes minute freshwater aquatic pond
creatures such as ciliates, euglenoids, protozoa, unicellular algae, and small
invertebrates.
Theoretical models of predator–prey relationships were suggested in 1925 by the
American biophysicist Alfred J. Lotka (1925), with an example being his publication
“Elements of Physical Biology” (Lotka 1925). An Italian mathematical biologist
Vito Volterra (1926) also dealt with a similar subject. Those efforts led to a finding
that the interaction between predator and prey has a regular (cyclical) fluctuation.
An interesting microbial relationship has been described between the ciliate
Paramecium bursaria and a yeast Schizosaccharomyces pombe. This biocenosis
was studied in laboratory conditions and a periodical oscillation of representatives of
both species was noted. An increase in the number of predator cells in that mixed
species population typically leads to a fast reduction in the cell number of the prey
population, i.e., the yeast. That consequence greatly lowers the nutrition availabile
for the Paramecium, stops development of the Paramecium population and the
number of Paramecium organisms then drops significantly. That reduction in predator population can possibly lead to an increase of the number of yeast cells and thus
the whole situation would cyclically repeat.
In other microbial populations, a certain balance between the predator and the
prey populations develops. The numbers of both species then do not periodically
change and instead stay at relatively constant levels. The situation in the rumen of
ruminants is quoted as an example of such balance. The lysis of intact bacteria by the
action of myxobacteria having the ability to secrete extracellular enzymes is sometimes also presented as a predation, as previously mentioned.
15.7.1 Bdellovibrio bacteriovorus as a Predator Bacterium
From Greek bdella ¼ leach and from Latin vibrare ¼ tremble. This predator
bacterium was described in detail by Heinz Stolp and Mortimer P. Starr in 1963
(Stolp and Starr 1963). It is a tiny, curved, rod-shaped, strictly aerobic bacterium,
about 0.3–04 Â 0.8–1.2 μm in size. It obtains energy by oxidation of amino acids
and acetate via the citric acid cycle. It features a biphasic life cycle. The cycle is
characterized by an alternating nongrowing phase, with a free-living predator phase
in which the organism reproduces. Although Bdellovibrio bacteriovorus has only
one flagellum, it is very mobile in the water environment. In one second it can cover
a distance equal to 100 times its length, while E. coli, for instance, at the same time
travels over a distance of only ten times its length. Parasitic strains of Bdellovibrio
bacteriovorus have a unique ability to parasitize some bacteria and they attack only
Gram-negative bacteria.
Bdellovibrio bacteriovorus penetrate into the periplasmatic space of their target,
between the cellular wall and the cytoplasmatic membrane. Within this space, they
use the host cell as a substrate for Bdellovibrio development and multiplication.
Gram-positive bacteria lack the periplasmatic space and thus Gram-positive bacteria
cannot be infected by Bdellovibrio. Penetration of the cellular wall of the host
254
V. Klaban
creatures such as ciliates, euglenoids, protozoa, unicellular algae, and small
invertebrates.
Theoretical models of predator–prey relationships were suggested in 1925 by the
American biophysicist Alfred J. Lotka (1925), with an example being his publication
“Elements of Physical Biology” (Lotka 1925). An Italian mathematical biologist
Vito Volterra (1926) also dealt with a similar subject. Those efforts led to a finding
that the interaction between predator and prey has a regular (cyclical) fluctuation.
An interesting microbial relationship has been described between the ciliate
Paramecium bursaria and a yeast Schizosaccharomyces pombe. This biocenosis
was studied in laboratory conditions and a periodical oscillation of representatives of
both species was noted. An increase in the number of predator cells in that mixed
species population typically leads to a fast reduction in the cell number of the prey
population, i.e., the yeast. That consequence greatly lowers the nutrition availabile
for the Paramecium, stops development of the Paramecium population and the
number of Paramecium organisms then drops significantly. That reduction in predator population can possibly lead to an increase of the number of yeast cells and thus
the whole situation would cyclically repeat.
In other microbial populations, a certain balance between the predator and the
prey populations develops. The numbers of both species then do not periodically
change and instead stay at relatively constant levels. The situation in the rumen of
ruminants is quoted as an example of such balance. The lysis of intact bacteria by the
action of myxobacteria having the ability to secrete extracellular enzymes is sometimes also presented as a predation, as previously mentioned.
15.7.1 Bdellovibrio bacteriovorus as a Predator Bacterium
From Greek bdella ¼ leach and from Latin vibrare ¼ tremble. This predator
bacterium was described in detail by Heinz Stolp and Mortimer P. Starr in 1963
(Stolp and Starr 1963). It is a tiny, curved, rod-shaped, strictly aerobic bacterium,
about 0.3–04 Â 0.8–1.2 μm in size. It obtains energy by oxidation of amino acids
and acetate via the citric acid cycle. It features a biphasic life cycle. The cycle is
characterized by an alternating nongrowing phase, with a free-living predator phase
in which the organism reproduces. Although Bdellovibrio bacteriovorus has only
one flagellum, it is very mobile in the water environment. In one second it can cover
a distance equal to 100 times its length, while E. coli, for instance, at the same time
travels over a distance of only ten times its length. Parasitic strains of Bdellovibrio
bacteriovorus have a unique ability to parasitize some bacteria and they attack only
Gram-negative bacteria.
Bdellovibrio bacteriovorus penetrate into the periplasmatic space of their target,
between the cellular wall and the cytoplasmatic membrane. Within this space, they
use the host cell as a substrate for Bdellovibrio development and multiplication.
Gram-positive bacteria lack the periplasmatic space and thus Gram-positive bacteria
cannot be infected by Bdellovibrio. Penetration of the cellular wall of the host
254
V. Klaban