Diatom-diazotroph associations

Figure 4.2 Conceptual model for differing fates of filamentous cyanobacterial diazotrophs (A) compared to diatom-diazotroph associations (B), from Subramaniam e(a/.,2008.

For the purpose of this text on symbioses as they relate to the marine nitrogen cycle, we wiU first emphasize the more common open ocean diatom-diazotrophic associations (DDAs), then summarize the recent advances in our understanding of sponge-nitrifying microbial associations, and provide brief introductions to a few other relevant symbioses. In addition, we recommend, the chapter by O Neil and Capone (Chapter 21) for details on algal-animal symbioses of Coral Reefs as they relate to the nitrogen cycle. Chapter 4 by Carpenter and Capone on Nitrogen Fixation and Chapter 5 by Ward on Nitrification. 

Whereas Trichodesmium is buoyant and resides largely in the upper layers of the water column, endosymbiotic Richelia may be more prone to gravitational settlement to deeper layers in their diatom hosts (Scharek et al, 1999a,b Subramaniam et al, 2008) (Fig. 4.2). Tropical river plumes may be particularly important sites of diazotroph-diatom associations (Voss et al, 2006 Subramaniam et al, 2008). 

As mentioned, diazotrophic diatom associations (DDAs) can, at times, be of quantitative significance. A bloom of the endosymbiont Richelia intracellularis within... 

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