Bacteria that Derive Nutrients from Other Organisms

Some bacteria obtain nutrients directly from other organisms. Bdellovibrio species do this by preying on other bacteria, attacking them and digesting their contents, eventually killing them. Bioluminescent bacteria use another tactic; they have established relationships with fish and squid in which the animal provides nutrients and protection while the bacterium provides a source of luminescence. Legionella species can live intracellularly within the protected confines of protozoa.

The Genus Bdellovibrio

Bdellovibrio species (bdello, from the Greek word for "leech") are highly motile Gram-negative bacteria that prey on E. coli and other Gram-negative bacteria (figure 11.25). They are small, curved rods, approximately 0.25 mm wide and 1 mm long, with a polar flagellum. When a Bdellovibrio cell attacks, it strikes its prey with such a high velocity that it actually propels the prey a short distance. The parasite then attaches to its host and rotates with a spinning motion. At the same time, it synthesizes digestive enzymes that break down lipids and peptidoglycan. Within 10 minutes, a hole in the cell wall of the prey is formed. This allows the parasitic bacterium to penetrate, lodging in the periplasm between the cytoplasmic membrane and the peptido-glycan layer. There, over a period of several hours, Bdellovibrio degrades and utilizes the prey's cellular contents. It derives energy by aerobically oxidizing amino acids and acetate. The para site increases in length as it resides in the periplasm, ultimately dividing to form several motile daughter cells. When the host cell lyses, the Bdellovibrio progeny are released to find new hosts, repeating the growth and reproduction cycle.

Bioluminescent Bacteria

Some species of Photobacterium and Vibrio can emit light (figure 11.26). This phenomenon, called bioluminescence, plays an important role in the symbiotic relationship between some of these bacteria and specific types of fish and squid. For example, certain types of squid have a specialized organ within the ink sac that is colonized by Vibrio fischeri. The light produced in the organ is thought to serve as a type of camouflage, obscuring the squid's contrast against the light from above and any shadow it might otherwise cast. It appears that the squid provides nutrients to the symbiotic bacteria, facilitating their growth. Another example is the flashlight fish, which has a light organ in a specialized pouch below its eye that harbors bioluminescent bacteria. By opening and closing a lid that covers the pouch, the fish can control the amount of light released, which is believed to confuse predators and prey.

Luminescence is catalyzed by the enzyme luciferase. Studies of the regulation of its synthesis revealed that the genes encoding it are only expressed when the density of the bacterial population reaches a critical point. This phenomenon of quorum sensing is now recognized as an important mechanism

Bacteria Cycle Atacting

Figure 11.25 Bdellovibrio (a) Color-enhanced transmission micrograph of Bdellovibrio bacteriovorus attacking its prey. (b) Life cycle of B. bacteriovorus. Note that the diagram exaggerates the size of the space in which B. bacteriovorus multiplies.

Figure 11.25 Bdellovibrio (a) Color-enhanced transmission micrograph of Bdellovibrio bacteriovorus attacking its prey. (b) Life cycle of B. bacteriovorus. Note that the diagram exaggerates the size of the space in which B. bacteriovorus multiplies.

(a)

Figure 11.26 Luminescent Bacteria (a) Plate cultures of luminescent bacteria. (b) Photograph of a flashlight fish; under the eye is a light organ colonized with luminescent bacteria.

11.7 Thriving in Aquatic Environments 289

Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

Get My Free Ebook


Responses

  • Ferruccio
    How bdellovibrios predate on other orgaisms?
    2 years ago
  • christina
    What kind of bacteria obtain nutrients from other organisms?
    1 year ago

Post a comment