MIT Research Finds Microbial Interactions Affecting Oceanic Carbon Cycles
Marine organic particles carry carbon from the surface to the deep every year worldwide. This phenomenon is made possible by the groups of marine microorganisms that gather on and collectively degrade sinking organic particles.
The mystery here is how these microorganisms self-assemble into communities and collectives, and how this affects particle degradation.
Massachusetts Institute of Technology (MIT) graduate student Manoshi S. Datta, Department of Civil and Environmental Engineering professors Otto X. Cordero and Martin Polz, and Department of Physics professor Jeff Gore collaborated to find out how to characterize these communities and their processes.
They published their research, “Microbial interactions lead to rapid micro-scale successions on model marine particles” on Nature Communications.
The microorganisms that bear down on sinking organic particles vary widely in age, size, and chemical composition. Researchers wanted to know how the process happens.
The scientists took a “semi-wild approach”. They immersed synthetic, chemically-defined particles in coastal seawater. Then they watched and observed how these particles assembled.
The results reveal that these particles self-assembled into communities through rapid sequential turnovers: Specific bacterial groups attach themselves to a particle, but then leave after a few hours, only to be replaced by a new group.
This behavior follows a pattern called “primary succession”. In this process, the first bacterial taxonomic group or “pioneers” dominate the community. Then, they pave the way for “secondary consumers”.
The pioneers are the ones who seek out and degrade particles.
The secondary consumers, meanwhile, can’t degrade particles, but can use the metabolic byproducts from the pioneers to grow.
The researchers say that this phenomenon is evident in temperate forests; it was only during the study that they learned it also applied to marine particles, only at a much shorter and quicker rate.
Cordero, the senior author of the study, said,
“Our results suggest that the existing theory of successions that has been developed for plants and animals may be applicable to complex natural microbial communities. This could provide a basis for linking microbial community structure to their population dynamics and activity.”
The study also reveals that the marine microbial succession undergoes a transition different from that of plants and animals: They shift from being determined by particle nutrients to that of the byproducts from the pioneers.
This would mean that the microbial communities in the ocean are composed of secondary consumer bacteria that don’t degrade particles, but rely only on their interactions with the pioneers.
Although small and invisible to the naked eye, the microbes’ interactions reveal a much larger concern. Cordero said,
“We think these interactions between microbes — where the majority exploits the effort of the pioneer minority — may end up having major effects on carbon turnover in the ocean.”
The data from the study might focus on tiny organisms, but its impact is a large one.
Stephen Lindemann, senior research scientist at the Pacific Northwest National Laboratory, said,
“This data importantly suggests that close interactions with particle-degrading microbes sustains a high diversity of secondary consumers in marine particle-associated communities. Ultimately, all microbial politics is local, too, and the sheer amount of marine snow means local microbial interactions within these communities may drive carbon cycling at whole-ocean scales.”