On Giant Seaweed, an Intimately Packed Microbiome

"Kelp Forest Blues," intaglio print by Brooke Weigel, co-author of a new paper visualizing the microbiome of a kelp that creates massive, underwater forests. Photo courtesy of Brooke Weigel

Giant, underwater kelp forests can tower up to 150 feet high, but don’t forget: Like many living things, kelp survival depends on microorganisms associated with its surface.

So when MBL’s Jessica Mark Welch gave a talk on the “amazing spatial structure we see in the bacterial communities of the human mouth and gut” at the University of Chicago, Cathy Pfister’s ears perked up. Pfister, a professor of Ecology and Evolution, wondered if the pioneering techniques Mark Welch’s lab had developed for imaging bacterial community structure could be used to look at microbes on marine surfaces, such as mussel beds or maybe kelp.

Thus germinated a collaboration to visualize the microbes on bull kelp (Nereocystis luetkeana), a canopy-forming species that grows extremely fast (up to 2 cm a day). Canopy-forming kelp are ecologically significant, fixing teragrams of carbon per year in coastal ecosystems. And the bacteria associated with the kelp’s surface synthesize essential vitamins, prevent biofouling, and provide signals that are necessary for normal kelp development. The kelp-bacteria symbiosis is not only ecologically important, it’s a potentially tractable model system for investigating the principles of host-microbe biology.

Last week, the team’s colorful results were published in Microbiome, including this great video summary:

Remote video URL

Brooke Weigel, then a PhD student in Pfister’s lab, collected samples of bull kelp from coastal Washington State and preserved them for imaging. Back in Mark-Welch's lab, Tabita Ramírez-Puebla began exploring the kelp microbiome using probes that Cathleen Schlundt had developed to look at the microbiome of marine plastic debris. Loretha Jack helped with the imaging. “And the rest is history!” Mark Welch says.

Jessica Mark Welch at center and lab members near Eel Pond in Woods Hole
From left, former MBL post-docs Tabita Ramírez-Puebla and Cathleen Schlundt, Jessica Mark Welch, Loretha Jack (former REU student at MBL), and Anna Knochel (former Woods Hole PEP student) in 2018. Credit: Julian Torres-Morales

Pfister co-directs and Mark Welch is a member of the Microbiome Center, a collaboration between MBL, University of Chicago, and Argonne National Laboratory. Dedicated to understanding the role of microbiomes across all kinds of environments, from deep ocean to the human body, the Microbiome Center is an outstanding example of a research synergy that formed in the wake of the UChicago-MBL affiliation in 2013.

Cross-secctional image of kelp microbiome
Cross-sectional image of kelp blade showing microbial biofilm on both sides of the blade. Credit: Ramírez-Puebla et al., Microbiome (2022)