bacteria by Bdellovibrio bacteriovorus occurs by enzymatic action of this predatory
bacterium, whereby Bdellovibrio enzymes open up a hole in the wall. Through these
holes Bdellovibrio enters the host and settles down in the periplasmic space.
Following initiation of the infection, the host bacterium turns into an osmotically
stable spherical bdelloplast. Bdellovibrio elongates up to 20 times its original length
within that bdelloplast and this very long organism then forms cells that are later
released into the environment thanks to a subsequent lysis of the infected host cell.
The Bdellovibrio developmental process, starting from penetration, takes about
4 h and requires an actively metabolizing host cell. The burst size (the number of
progeny per one host cell) depends on the size of the host cell. It varies in amongst
microbes from about four Bdellovibrio cells with Escherichia coli up to about
20 Bdellovibrio cells in case of the much larger bacterium Aquaspirillum serpens.
In amongst microbes there is quite often a rather vague resolution between parasitism and predation. For example, the interaction between Bdellovibrio and a sensitive
Gram-negative cell is considered by some investigators as parasitism and by others is
considered as a predation.
It is worth noting that Bdellovibrio bacteriovorus also attacks Microcystis
aeruginosa and some other cyanobacteria (blue-green bacteria). Such infection of
cyanobacteria could be of ecological importance. Bdellovibrio are relatively common in nature and can be isolated from contaminated or wastewaters by methods
similar to those employed for examination of phages, with samples of water or soil
suspensions first filtered through a membrane filter, which holds back larger bacteria
and lets through Bdellovibrio. The filtrate is then inoculated onto the surface of an
agar substrate containing a host strain of bacteria. Following incubation, the
Bdellovibrio contained in the inoculum form plaques (negative colonies) on the
otherwise coherent growth, termed a lawn, of the host bacteria and Bdellovibrio can
be also isolated from these plaques. The plaques are round transparent spots, in
which the host bacteria have been killed by the predatory Bdellovibrio.
Bdellovibrio are capable of quite intensively attacking their host in laboratory
experiments; however, this parasitic relationship is quite weaker in the natural
environment. This parasitism of bacterium by Bdellovibrio is partially inhibited by
the presence of clay mineral particles, a fact established in 1978 by Margaret Roper
and Kevin Marshall (Roper and Marshall 1978). The clay particles possibly form a
sort of coating layer around the E. coli cells, preventing direct access of the predator
Bdellovibrio to the host cells. Also, it has been established that even the Bdellovibrio
can be attacked by specific bacteriophages (Hashimoto et al. 1970).
15.7.2 Myxococcus xanthus
Myxococcus xanthus belongs to Myxococcaceae family, alias Gymnomycota. These
microorganisms are known for their slippery mobility. They produce a whole range
of antibiotics and lytic compounds. Live host cells that they attack are killed by
antibiotic substances secreted by the Myxococcus and then the host cells lyse by the
action of a group of extracellular enzymes (Keane and Berleman 2016) mostly
15 Microscopic World and the Phenomenon of Symbiosis in the Natural Environment
255
bacterium, whereby Bdellovibrio enzymes open up a hole in the wall. Through these
holes Bdellovibrio enters the host and settles down in the periplasmic space.
Following initiation of the infection, the host bacterium turns into an osmotically
stable spherical bdelloplast. Bdellovibrio elongates up to 20 times its original length
within that bdelloplast and this very long organism then forms cells that are later
released into the environment thanks to a subsequent lysis of the infected host cell.
The Bdellovibrio developmental process, starting from penetration, takes about
4 h and requires an actively metabolizing host cell. The burst size (the number of
progeny per one host cell) depends on the size of the host cell. It varies in amongst
microbes from about four Bdellovibrio cells with Escherichia coli up to about
20 Bdellovibrio cells in case of the much larger bacterium Aquaspirillum serpens.
In amongst microbes there is quite often a rather vague resolution between parasitism and predation. For example, the interaction between Bdellovibrio and a sensitive
Gram-negative cell is considered by some investigators as parasitism and by others is
considered as a predation.
It is worth noting that Bdellovibrio bacteriovorus also attacks Microcystis
aeruginosa and some other cyanobacteria (blue-green bacteria). Such infection of
cyanobacteria could be of ecological importance. Bdellovibrio are relatively common in nature and can be isolated from contaminated or wastewaters by methods
similar to those employed for examination of phages, with samples of water or soil
suspensions first filtered through a membrane filter, which holds back larger bacteria
and lets through Bdellovibrio. The filtrate is then inoculated onto the surface of an
agar substrate containing a host strain of bacteria. Following incubation, the
Bdellovibrio contained in the inoculum form plaques (negative colonies) on the
otherwise coherent growth, termed a lawn, of the host bacteria and Bdellovibrio can
be also isolated from these plaques. The plaques are round transparent spots, in
which the host bacteria have been killed by the predatory Bdellovibrio.
Bdellovibrio are capable of quite intensively attacking their host in laboratory
experiments; however, this parasitic relationship is quite weaker in the natural
environment. This parasitism of bacterium by Bdellovibrio is partially inhibited by
the presence of clay mineral particles, a fact established in 1978 by Margaret Roper
and Kevin Marshall (Roper and Marshall 1978). The clay particles possibly form a
sort of coating layer around the E. coli cells, preventing direct access of the predator
Bdellovibrio to the host cells. Also, it has been established that even the Bdellovibrio
can be attacked by specific bacteriophages (Hashimoto et al. 1970).
15.7.2 Myxococcus xanthus
Myxococcus xanthus belongs to Myxococcaceae family, alias Gymnomycota. These
microorganisms are known for their slippery mobility. They produce a whole range
of antibiotics and lytic compounds. Live host cells that they attack are killed by
antibiotic substances secreted by the Myxococcus and then the host cells lyse by the
action of a group of extracellular enzymes (Keane and Berleman 2016) mostly
15 Microscopic World and the Phenomenon of Symbiosis in the Natural Environment
255