Predatory bacteria are native to many microbial communities and have
been found in terrestric and aquatic ecosystems, as well as in the human
and animal intestine. A research team at the Max-Planck-Institute for
Developmental Biology, together with their colleagues from the
universities of Nottingham and Bielefeld has now unraveled for the first
time the complete genome sequence of a predatory bacterium in order to
identify molecular mechanisms that are important when bacteria hunt
their own. Insights into this ancient dependency may give rise to novel
anti-microbial substances.
These substances, however, will not be based
on the structures of today's chemical antibiotics, but rather will be
deduced from the protein sequences that become available from the
Bdellovibrio genome project. Furthermore, the scientists predict in
their publication of this weeks edition of Science magazine that
Bdellovibrio may be developed into a therapeutic agent that could be
used as a "living antibiotic".
 |
| Life cycle of the predatory bacterium Bdellovibrio bacteriovorus (yellow). For reproduction it depends on a bacterial prey cell (blue). (Image: Max Planck Institute for Developmental Biology/Rendulic, Berger und Schuster) |
Bdellovibrio bacteriovorus is a fascinating predatory bacterium that
attaches specifically to certain other bacteria in order to invade them.
Once it has entered its prey, it begins to consume the host cell from
the inside. Using Bdellovibrio's genomic information the life cycle of
this unique bacterium can now be studied for the first time on a
molecular level.
In the free-living phase of its life cycle Bdellovibrio swims at high
speed while locating areas of high prey concentration by use of its
chemosensory system. Once it has collided with a prey cell, Bdellovibrio
stays reversibly attached to it while verifying its suitability for
invasion. In the presented model, the recognition mechanism is likely to
involve one of several pilus systems that produce long retractable
fibers that allow Bdellovibrio to pull itself into close proximity with
its prey. By using a lytic cocktail that is capable of degrading lipids,
proteins and carbohydrate molecules, Bdellovibrio then generates an
opening in the cell wall of the prey. Via a pulling motion the predator
navigates itself in the "periplasmic space" between the outer and inner
membrane of the prey cell.
Bdellovibrio can remain encysted at this stage, while the entry pore
has been sealed and the prey cell remains viable. Most commonly,
however, Bdellovibrio immediately enters its growth phase in which it
depends on the prey's amino acids. The amino acids and other nutrients
are made available to the invader by the degradation of biopolymers in
the cytoplasm of the prey cell and are subsequently transported into the
Bdellovibrio cell. In this way the cytoplasm of the prey is entirely
consumed, while the Bdellovibrio cell elongates. Upon exhaustion of all
prey resources Bdellovibrio's life cycle continues, with the bacteria
differentiating back into as many as 15 motile cells, which seek out and
attack new prey.
The genomic analysis of Bdellovibrio showed that this organism uses a
large variety of lytic enzymes, which can degrade complex biopolymers
of the prey, such as proteins, carbohydrates, DNA and RNA. The
researchers will attempt to identify the targets in the prey cell that
have proven to be successful points of attack in this million-year-old
prey-predator relationship. The lytic enzymes acting on cellular systems
that are not targeted by conventional chemical antibiotics are thereby
especially interesting.
Far reaching anti-microbial strategies aim at using Bdellovibrio as a
"living antibiotic". This seems feasible, as Bdellovibrio is not
capable of infecting eukaryotic cells, in particular mammalian cells.
Moreover, it was shown in animal experiments that Bdellovibrio only has a
weakly immunogenic surface, which does not produce serious life
threatening reactions in test animals. These attributes, together with
the facts that certain Bdellovibrio strains show a very narrow prey
spectrum and are capable of penetrating the same tissues as may
human-pathogens, gives promise to the development of novel
anti-microbial strategies.
Source:
Tidak ada komentar:
Posting Komentar