The ecological lifestyle of a keystone marine cyanobacterium

Conducting scientific research in the field requires patience, perseverance, and the ability to think creatively when things go awry

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The paper in Nature Microbiology is here: 

For microbiologists who study the open ocean, there are additional challenges with being at sea for several weeks or months.  To maximize chances of success, it is recommended to assemble a diverse, experienced field team of hardy scientists, and to conduct sampling that uses a combination of tried-and-tested methods together with novel technology.  During the summer of 2015, we conducted an intense study of microbial metabolism over diel timescales in the oligotrophic North Pacific Subtropical Gyre.  It was an extremely large expedition with 47 microbial oceanographers participating from the newly formed Simons Collaboration on Ocean Processes and Ecology (SCOPE) and from the Center for Microbial Oceanography: Research and Education (C-MORE).  The daily schedule was also intense with water-column sampling being conducted every 4 hours for 4 days and then repeated after a 48 hr break to catch up on sleep and conduct several contextual hydrographic surveys.

The result of these endeavors was an incredible insight into the physiology and ecological niche of Crocosphaera, a keystone microorganism which is considered vital to supporting new production in the oligotrophic environment.  Crocosphaera is a small unicellular cyanobacterium that was first isolated in the 1980s by John Waterbury.  It is a remarkable cyanobacterium due to its ability to photosynthesize during the day and fix nitrogen at night.  Like many microorganisms the majority of our previous knowledge about Crocosphaera derived from laboratory-maintained cultures, which provide an insight into cellular physiology but don’t provide values of in situ growth rates, mortality, rates of nitrogen fixation.  These parameters are needed to improve the models of nitrogen fixation and the distribution of diazotrophs in the global ocean.

As the title of the paper indicates, we measured the coordinated regulation of growth, activity and transcription in natural populations of Crocosphaera.  This information is embedded in the wider context of water-column biogeochemistry to discuss the contribution of Crocosphaera to productivity and export.  This collaborative effort was achieved through the selfless work of multiple scientists seeking to better understand the marine microbes that are the drivers of ocean biogeochemistry.  The exciting news is that there is more to come!  Simultaneous measurements were conducted for viruses, bacteria, photoautorophs and photoheterotophs, intracellular lipids, metabolites, and more.  A follow-up expedition recently returned to port with a fresh batch of samples and data.  With improved methods for tracking and sampling microbial communities, we are excited to see what new insights these data hold. 

Photo 1. A scientist contemplates what lies ahead as we depart from Honolulu harbor. Courtesy of Sarah Searson

Photo 2. Life around the CTD-rosette is similar to wildlife around the water-hole. We congregate at regular intervals to collect our water, have a quick chat, and then depart to our lab benches for processing the samples. Courtesy of Sarah Searson

Figure 3. A microbiologists dream come true. Tracking Crocosphaera cell abundances in real-time at 3 minute intervals using the SeaFlow, an underway flow cytometer.

Article: Wilson S.T.*, F. Aylward*, F. Ribalet, B. Barone, J.R. Casey, P. Connell, J.A. Eppley, S. Ferrón, J.N. Fitzsimmons, C.T. Hayes, A.E. Romano, K.A. Turk-Kubo, A. Vislova, E.V. Armbrust, D.A. Caron,  M.J. Church, J.P. Zehr, D.M. Karl, E.F. DeLong (2017) Coordinated regulation of growth, activity and transcription in natural populations of the unicellular nitrogen-fixing cyanobacterium Crocosphaera. Nature Microbiol. 2: 17118

 Written by Sam Wilson and Elisha Wood-Charlson on behalf of the coauthors

Sam Wilson

Researcher, University of Hawaii