"This combination of techniques is a great tool for microbiology because it couples phylogenetic identification with metabolic analysis," Thompson said. "We could see that the cyanobacteria were fixing the labeled nitrogen and transferring it to the host cells."
Genetic analysis of the host cell indicates its closest relative is the species Braarudosphaera bigelowii. In many species of prymnesiophytes, including B. bigelowii, the cells form external calcified plates, suggesting that the host cell in the symbiosis may have plates that are easily dislodged during processing of seawater samples. "That would be important, because cells with plates sink faster than other organisms, so the carbon they fix could end up being transported to the deep sea or the seafloor," Zehr said.
Zehr noted that it is very difficult to estimate the contribution of this symbiosis to global carbon and nitrogen cycles. Other algae are more abundant and probably much more important in terms of oceanic carbon fixation than the algal host in this symbiosis. But the cyanobacterial partner probably makes a significant contribution to global nitrogen fixation in the oceans, he said.
"Planktonic symbioses are very understudied and difficult to study, as the associations are often fragile
|Contact: Tim Stephens|
University of California - Santa Cruz