jueves, mayo 22, 2008
O presente ubíquo das simbioses em esponjas
A origem simbiótica de certos tipos celulares em filos animais basais - discutida em post anteriores (aqui, acá e nos comentários aqui) - recebe um bom apoio com os dados publicados em Science sobre a ubiquidade, abundância e diversidade de simbiontes em esponjas. Alguns trechos do artigo:
"One of evolution's more ancient animals, sponges at first glance seem quite simple--little more than loose consortiums of semiautonomous cells, stuck in one place filtering food from the water column. But a closer look reveals a surprising twist. "With many species, under the microscope you see almost exclusively bacteria" among the cells, says Piel, an organic chemist at the University of Bonn in Germany"
"These genetic studies uncovered a distinctive and extensive community, identifying more than 100 species of microbes that are found in sponges but not in the surrounding water. This distribution indicates that these bugs are long-term residents rather than passersby. An individual sponge might host dozens of different species, and overall, the molecular analyses have found an impressive variety: 14 bacterial phyla, two phyla of archaea, and several types of eukaryotic microbes."
"Microbes might have colonized a sponge early in the group's evolutionary history and acquired characteristics that enabled them to live in sponges full-time, Taylor proposes. Those sponge-loving microbes could have then spread to other sponges--and other oceans. And such a scenario could explain what may be a new phylum called Poribacteria, after Porifera, Latin for "sponge." Poribacteria have been found throughout the world, albeit exclusively in sponges."
"Whatever their function, the microbes seem important enough for sponges to pass on to future generations. In the female sponge, nurse cells, which provide the "yolk" for developing eggs, also ferry blue-green algae from the sponge's outer layers to the developing oocytes located deeper in the sponge matrix. In 2005, Kayley Usher and her colleagues at the University of Western Australia in Perth even found blue-green algae in the sperm of the sponge Chondrilla australiensis. A year later, Julie Enticknap, a postdoctoral fellow in Hill's lab, was able to culture a sponge-dwelling alphaproteobacterium from the larvae of a sponge collected off the coast of Florida, another indication of possible parent-to-offspring transmission."
"But that study highlights what may be the most baffling mystery in sponge microbiology. Usually when symbionts are passed from parent to offspring, the partners undergo what is called cospeciation, and the microbes develop a unique genetic signature and become confined to that particular host. "But that doesn't happen here," says Hentschel. The bacteria in the larvae proved closely related to those cultured from unrelated sponges growing in Jamaica, Indonesia, and the Chesapeake Bay in the United States. The best explanation for the broad distribution of this bacterium--and for many other species found across the globe--she says, is that sponges acquire their resident bacteria both from their parents and from the environment."
O trabalho termina falando em "sea-based drugs"... O que fica absolutamente claro é que a incorporação de simbiontes em organismos marinhos filtradores como esponja e hidrozooários não deve ser visto como um fenômeno raro.
The Inner Lives of Sponges. Gretchen Vogel (23 May 2008) Science 320 (5879), 1028.