Now published in ISME by Foster et al: The rate and fate of N2 and C fixation by marine diatom-diazotroph symbioses

Impact: Our study reports on planktonic N2-fixing symbioses that are ubiquitously distributed and considered important to both the N and C cycles, yet our understanding of how the partners acquire (and share) elements necessary for their physiology and growth is still poorly characterised. Using stable isotopically labelled substrates and a high-resolution secondary ion mass spectrometry approach on natural populations treated with and without inhibitors allowed us to trace and quantify the impact of in situ conditions, and in addition, how the metabolic activity changes in the absence of the host. Results showed that the hosts are nearly as important in these partnerships, or symbiosis, as the symbionts. Thus, despite the symbionts ability to fix their own C, they relied on their respective hosts for C. This work expands on earlier and similar recent works that have reported single cell metabolic rates, by applying the single cell measures to a theoretical model to predict the N flux to the surround. We estimated growth rate parameters, cell to cell interactions and metabolic activity in natural populations, which are relevant to other symbiotic systems (i.e., terrestrial, coral reefs).

Read the full article here: https://www.nature.com/articles/s41396-021-01086-7

Collaborators (Names, titles, universities) : Angel White (University of Hawai'i), Martin Whitehouse (NORDSIM, and also AMRI PI), Marcel MMM Kuypers, Daniela Tienken, Sten Littmann (MPI Bremen)

Representative epi-fluorescent micrographs and NanoSIMS imaging of wild collected symbiotic diatom-Richelia symbioses incubated with 15N2 and 13C-bicarbonate for 12 h under in situ conditions.

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Congratulations to AMRI co-PI Rachel Foster and her collaborators on their newly published article in The ISME Journal

New paper published in Nature Communications, Mehrshad et. al: Energy efficiency and biological interactions define the core microbiome of deep oligotrophic groundwater

AMRI researcher Maliheh Mehrshad and co-authors have recently published in Nature Communications on energy efficiency and biological interactions in deep oligotrophic groundwater. Alongside co-authors and fellow AMRI researchers Margarita Lopez-Fernandez, John Sundh, Emma Bell, Domenico Simone, Moritz Buck, Rizlan Bernier-Latmani, Stefan Bertilsson, and Mark Dopson, Mehrshad et al. was published in July of this summer, you can read it here!

A summary from first author Maliheh Mehrshad:

There are numerous fictional accounts of how man explores subterranean life. Jules Verne’s “Journey to the Center of the Earth” pictured an underground ocean and living prehistoric creatures in professor Lidenbrock’s adventure down a volcanic tunnel. But really, if we take the fiction out of the equation; what has science taught us about life below the surface?

One environment that has been probed to explore subsurface life is groundwater. Groundwater environments are extremely oligotrophic, meaning that they are very scarce in nutrients and energy to sustain life. However, recent evidence has settled the long-running debate that the deep subsurface contains active life from all domains and viruses. Studies estimate that Archaea and Bacteria have a total abundance of a staggering 5×1027cells in deep groundwater environments and represent the base of the food web. However, important ecological and evolutionary questions regarding their adaptations and mode of life remain unanswered. Microbes attuned to the low-end of the bioenergetics spectrum have specific adaptations to occupy these extremely oligotrophic environments, but we know very little about what these adaptations are.

Studying deep groundwater environments is limited by access and there are few places on earth where it is possible to assess microbial diversity and function in these ecosystems and study how they are constrained by factors such as bedrock lithology, available electron donors and acceptors, depth, and hydrological isolation from the photosynthesis-fueled surface. The fortunate presence of two disconnected access points in the same lithology of the Fennoscandian Shield bedrock provided us with a unique opportunity to understand the ecology and evolution of deep groundwater microbiome.

Our comparative genome-resolved analysis of the prokaryotic community in growndwater flowing in the Fennoscandian Shield at Äspö HRL, Sweden and Olkiluoto Island, Finland, shows that the oligotrophic deep groundwaters have a shared deep groundwater core microbiome. This means we found the same species of Archaea and Bacteria in both of these locations. This finding can provide clues to how the deep groundwater community is developing. We show that deep groundwater ecosystems foster highly diverse, yet cooperative microbial communities adapted to this setting. Our results reveal that this life survives by cooperating in mutually beneficial partnerships, such as by helping each other with compounds needed for growth. These microbes adapt to the low energy availability of the deep groundwater by growing in short bursts and then halting growth and waiting for more energy to resume their life-cycle. Our results help explain how life can survive in the deep groundwater where extremely little energy is available. We suggest that instead of a lifestyle where microbes predominantly invest in functions related to maintenance and survival, an episodic and cooperative lifestyle ensures the subsistence of the deep groundwater microbiome.