Wednesday, June 27, 2012

The Curious case of Bdellovibrio: Beware Bacterias!

In my class 12, our teacher was teaching us bacterial taxonomy. And, he said “Beware Escherichias, we are reading Bdellovibrio.” The first impression was it was some kind of Bacteriophage, but we were damned to hear that it was actually a bacteria. While I remembered the incident, I almost forgot the name of  the bacteria. It was untill yesterday, that I was reading about Virophage(sputnik.. isnt it a funny name?), I remebered what my teacher said then.
While surfing Internet I went thorough one blog, which read, “A mild ocean breeze plays over the water surface, dispelling any notion that danger lurks in the murky depths. However, a gruesome event is about to occur as a silent attacker speeds forth toward an unsuspecting victim. In a furious collision, the savage meets its target and whittles its way into the body of the innocent prey. Once inside, the transformation begins - the predator ceases its frenzy and prepares to multiply. The host is reduced to a protective cocoon, supplying food and shelter for the growing parasite. Within hours, the nourishment is drained and the ghost-like shell of the host bursts open to release a new generation of deadly predators. And all the while, the waters remain still...’’
This, actually summarizes what Bdellovibrio actually is. The Bdellovibrio (which literally means "curved leech") make a living by attacking and devouring other bacteria, and are found in diverse environments such as marine and fresh waters, sewage, and soil. The predatory bacterium Bdellovibrio bacteriovorus eats its prey-larger bacteria, such as Escherichia coli, from the inside, an example of the imaginative lengths to which some prokaryotes will go to make a living.  Discovered in 1962, their lifestyle has made them hard to follow with conventional tools. It has typically two phases in its lifecycle, Attack phase and Growth Phase.

In attack phase, B. bacteriovorus swims at high speed using a single sheathed polar flagellum with a characteristic dampened filament waveform. Once B. bacteriovorus has collided with a prey cell, Gram negative Bacteria, it remains reversibly attached to it for a short "recognition" period , after which it becomes irreversibly anchored via the pole opposite the flagellum. Before invasion of the prey cell can be achieved, B. bacteriovorus generates a small opening in the prey cell's outer membrane and peptidoglycan layer, which is ultimately resealed. A mixture of hydrolytic enzymes is applied in a locally targeted manner that prevents excessive damage to the prey and counters diffusion.Once inside, the attacker loses its flagellum and prepares for the multiplication process.
Now the Bdellovibrio is in the growth phase and lies in the periplasmic space of the prey.  During the growth phase the Bdellovibrio becomes immobile.  Also, unlike the attack phase, it can now carryout RNA, DNA, and protein synthesis.  The host cell envelope is converted into a bdelloplast, envelope with drastically altered morphology and composition.  It allows easy access of extracellular and intracellular components to the Bdellovibrio.  The Bdellovibrio uses the hosts cellular components for building blocks in cell division.  This is not to be confused with a virus, Bdellovibrio doesn’t rely on the host cells metabolism.  The invaded cell is used only as a source of organic substrates.  The growth phase cell has indeterminate growth, depending on the quantity and quality of the surrounding environment.  The cell elongates and spirals.  It grows into a septate filament, which fragments into flagellated attack phase cells once growth has ceased.  This causes the host cell to lyse, killing the host cell and freeing the attack phase Bdellovibrio cells to find more prey.
With ‘almost’ virus like characters, Bdellovibrio, actually shows how much the bacterias can accliminate to survive.The area of Bdellovibrio biology is concerned with understanding the metabolic adaptations of the Bdellovibrios life cycle.  This allows us to help define the attack phase and growth phase, give insight into the versatility of bacterial metabolism, and recognize the convergence among many microorganisms dependent on the intracellular environment. There are three main applications the Bdellovibrio is being used for. First, it can be used to detect certain pollutants my measuring the decrease in attack phase activity caused by the pollutant. Second, the Bdellovibrio may play a natural role in water purification. Lastly, the most widely used application is to study the Bdellovibrio for discovery of biochemical and physiological capabilities that have allowed the adaptation of life in an intracellular environment.
Could the host cell be supplying an essential nutrient? A vitamin? Perhaps a protein or two? Studies show that normal Bdellovibrio can multiply without living host cells under certain conditions. If the soluble components are extracted from host cells and fed into a beaker containing only Bdellovibrio, the Bdellovibrio are able to grow and multiply. This suggests that there is a factor which Bdellovibrio needs in order to survive - and only prey bacteria can provide! We are still searching for the factors that control the host-parasite relationship and we are continuing to make new discoveries. Meanwhile, Bdellovibrio remains a fierce predator in the natural environment.