Mopping Up Little Helpers

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Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1842
DOI: 10.1126/science.314.5807.1842c

Sponges (Porifera) hold an interesting evolutionary position (sitting between the choanoflagellates and other animals), being conglomerations of cells, with some functional and morphological differentiation, loosely organized around a spongocoel cavity. Many sponges host an array of prokaryotes, some of which may accumulate passively as the sponge filters seawater; indeed, one view is that the sponge cells serve merely as an inert scaffold for prokaryote communities.

However, Sharp et al. show in a 3-year study that this association can persist beyond happenstance. They find that sponge embryos travel with a contingent of prokaryotes that are inherited vertically, implying that there are selective mechanisms of transmission and recruitment. Like the somatic cells of the sponge, the prokaryotic denizens display a functional differentiation, with some specializing in sulfur oxidation or nitrogen fixation, and they probably contribute to mutualistic nutrient cycling within the sponge. Furthermore, some of the bacteria appear to produce bioactive compounds, which may aid host defenses. — CA

Appl. Environ. Microbiol. 10.1128/AEM.01493-06 (2006).

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