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Ch.26 Seminar Report


I. New Species of Carnivorous Sponge

A new species of sponge was discovered in Marseille, France by Jean Vancelet and Nicole Boury-Esnault of the Universite d’ Aix-Marseille II. The sponge was found at a depth of between about 17 and 20 meters. At first the sponge seemed to resemble the deep-sea cladorhizid sponges, which are found closer to the surface and are commonly used for scrubbing dirt off bathtubs. However the new species was classified in the genus Asbestopluma, which holds the depth record among all genera of sponges of 8, 840 meters.

The first indication of something strange in this sponge is the absence of the characteristic choanocytes, or collar cells, and aquiferous system of tubes and tunnels used by typical sponges to filter feed. Instead the sponge has spiky filaments with hooked spicules. Initially scientists thought that the sponge feed by means of some form of passive phagocytosis. Then it was observed that the sponges used these spicules, which provide a Velcro™-like adhesives, to trap small crustaceans, usually about 1 mm in length. New filaments grow over and completely envelop the prey after about twenty-four hours and the catch is digested after a few days. The spicules do not use toxins or cause paralysis of any kind because the prey was observed struggling for several hours after its capture.

It is hypothesized that this sponge evolved it new feeding system as a result of living in an extreme environment with cold water and limited nutrients. It is possible that the sponge was first carried there from a deep-sea canyon by strong currents. This new species, still unnamed, has confused taxonomists because it is a sponge but, as Vancelet states, “The definition of the phylum, based on the aquiferous system and...choanocytes, is now inadequate.”

II. Cnidarians that Glow

There are certain species of coral found in the Red Sea that fluoresce when exposed to ultraviolet light. This phenomenon was first noted in 1964 by marine biologist René Catala of New Caledonia in his book Carnival Under the Sea. Experiments by David Fridman, founder of Coral World in Elat, Israel, show that the corals absorb ultraviolet light and emit visible light producing a variety of fluorescent colors. He states that, “...ultraviolet lights commonly used for black-light posters worked best on corals.”

When the coral is viewed in normal underwater daylight they look blue-ish green because the sea filters out most of the colors of the visible light spectrum. An electronic flash used underwater with the coral gives it an out-of-water appearance because the flash brings back the colors of the spectrum. When exposed to ultraviolet light from an HMI high-intensity light with ultraviolet filter the coral glows brightly. The reason for this is still unclear, but as stated by Charles Mazel of the Massachusetts Institute of Technology, “It’s been suggested that fluorescence aids photosynthesis or that it protects against too much ultraviolet light. But there is a real possibility that corals fluoresce for no reason at all.”

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The Pacific Northwest jellyfish, Aequora victoria, glows as a result of a chemical known as green fluorescent protein, or GFP. This chemical also blinks when exposed to a laser and is one of the first larger molecules to do so at room temperature and at “normal biological conditions.” GFP is a barrel shaped molecule, sometimes said to be similar in shape to a Chinese finger puzzle, with a coil of three amino acids in the center that act as a light emitting chromophore. The green glow of GFP is a result of the collapse of one turn of the coil to from a ring.

Scientists examined mutant forms of GFP that give off a brighter glow than the normal blue-green. When exposed to light at a wavelength of 488 nm the protein emitted light for several seconds then darkened then became light again. This cycle repeated itself for several minutes until the protein got dark and seemed to turn off forever. Exposure to light at a wavelength of 405 nm caused the darkened protein to reactivate. After this, exposure to the original light resulted in blinking again.

This and other mutant forms of GFP has some practical uses. The blinking properties of it give GFP potential for use as an optical data storage medium, one bit of data can be stored on one molecule. The glowing properties make it useful as tool for tracking proteins in living cells. By altering the color of the glow of GFP scientists gain insight on the how the human eye responds to different colors.

III. Nematodes and Bacteria

It has been found that Heterorhabditis nematodes carry the bacteria Photohabdus luminescens in its intestinal tract. These nematodes and bacteria share an interesting symbiotic relationship. The nematodes are clear, about a millimeter long, and about the width of a human hair. When the worm encounters a insect larva, it enters through the mouth or another opening. Then it bores a hole through the insect’s circulatory system and expels the bacteria from its intestines. The bacteria release, among many other chemicals, a red pigment that behaves like an antibiotic. This causes the insect to turn a brick red color. Within 24 hours the insect is dead at the hands of the toxins released by the bacteria. The corpse is consumed by the same bacteria which begin to glow using the enzyme luciferase. Luciferase causes the light-emitting biological reaction that is normally used by certain kinds of marine bacteria. Meanwhile the nematode is preparing to reproduce hermaphroditically. It fertilizes and lays its eggs which hatch into new nematodes. After about ten to fourteen days the nematode larvae stop ingesting the bacteria as nourishment and instead as symbionts. Why this shift occurs is still unexplained. Then the nematodes emerge from the dead insect and return to the soil.

The bacteria themselves are enigmatic as well. They produce a great variety of chemicals that it seems that, “Phylogenically, they shouldn’t be doing what they’re doing,” said environmental microbiologist Kenneth H. Nealson of the University of Wisconsin-Milwaukee’s Center of Great Lakes Studies. First of all there’s the luminescence which is usually found in marine bacteria. It’s been suggested that the bacteria could have acquired this genetic sequence from a virus through transduction. Other substances produced by the bacteria are microbial antibiotics. These are most likely produced to keep away competitive decomposers from the dead insect body. They also produce pigments known as anthraquinones which are similar in structure as certain antibiotics produced by other bacteria. Crystalline compounds produced by the bacteria were initially thought of to be the insect killing agent. Injecting the crystals into insects had no effect. However when bacteria were mutated so they didn’t have the ability to make the crystals they could not exist symbiotically with the nematodes. Chemical analysis revealed that the crystals were a protein rich in the amino acids methionine and lysine. The toxin produced by P. luminescens that kills insects is a complex of several proteins. However it is only effective when it was injected into the insect by the nematode. Another bacteria, Xenorhabdus, which also lives symbiotically with another nematode, Steinernema, produces antibiotics that work against bacteria that attack plants, animals, and people. These bacteria also produce an enzyme called chitinase that attacks that chitin in fungi.

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