Microbial Communities and Biogeochemistry in Marine Sediments of the Baltic Sea and the High Arctic, Svalbard

Marine sediments contain more microorganisms than all of the world’s oceans, with current of estimates of 1×1029 microorganisms. Despite marine sediments being replete with microbial cells, the majority of these microorganisms remain uncultured in the laboratory. At present, it is estimated that over 99% of all microorganisms have evaded culture, although truer estimates likely depend upon environment. Factors responsible for the intractability of these microorganisms include very slow doubling times, predicted to be on the orders of years to centuries, as well as special physiological needs of extremophiles. Unsuccessful laboratory growth of these microorganisms requires us to rely on culture-independent tools, including molecular techniques, metagenomics, and bioinformatic tools to glean insight into their ecological structure and function.This dissertation combines molecular and bioinformatic techniques to evaluate the biosphere within deeply buried sediments of the Baltic Sea and shallow sediments in Arctic fjords. Quantification of microbial biomass within marine sediments lays the groundwork for questions related to organic carbon and element cycling. Although essential, reliable and reproducible estimates of microbial biomass within deeply buried sediments has proved challenging. Here we present an interlaboratory comparison of quantification results from International Ocean Discovery Program Exp. 347 sediments that allowed us to define best practices that lead to meaningful quantification estimates. We then transferred these best practices to marine sediments in a Svalbard fjord (Van Keulenfjorden) to understand how glacial proximity influences microbial communities. Through 16S rRNA gene libraries, organic geochemistry, and genome reconstruction, we illustrate that cross-fjord trends in organic matter influence community structure in the sediment. In addition, we argue that biological iron and sulfur cycling facilitates rapid recycling of electron acceptors crucial for carbon oxidation. We delved deeper into their metabolic pathways with metagenomic sequencing and contig binning. We reconstructed several genomes of the Woeseiaceae clade that can act both as a sink and a source of carbon. Ultimately, our work provides a framework for understanding how glacial proximity influences microbial community composition and metabolic function, which is important and timely with ongoing climate change and a strong threat of severe glacial retreat in this region

Draft Genome Sequence of Antarctic Methanogen Enriched from Dry Valley Permafrost

A genomic reconstruction belonging to the genus Methanosarcina was assembled from metagenomic data from a methane-producing enrichment of Antarctic permafrost. This is the first methanogen genome reported from permafrost of the Dry Valleys and can help shed light on future climate-affected methane dynamics

The helium and carbon isotope characteristics of the Andean Convergent Margin

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Barry, P. H., De Moor, J. M., Chiodi, A., Aguilera, F., Hudak, M. R., Bekaert, D. V., Turner, S. J., Curtice, J., Seltzer, A. M., Jessen, G. L., Osses, E., Blamey, J. M., Amenabar, M. J., Selci, M., Cascone, M., Bastianoni, A., Nakagawa, M., Filipovich, R., Bustos, E., Schrenk, M. O. , Buongiorno, J., Ramírez, C. J., Rogers, T. J., Lloyd, K. G. & Giovannelli, D. The helium and carbon isotope characteristics of the Andean Convergent Margin. Frontiers in Earth Science, 10, (2022): 897267, https://doi.org/10.3389/feart.2022.897267.Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in 3He/4He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of 4He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ13C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/3He values that vary by over two orders of magnitude (6.9 × 108–1.7 × 1011). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/3He values vary by over four orders of magnitude (4.7 × 107–1.7 × 1012). Low δ13C and CO2/3He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.This work was principally supported by the NSF-FRES award 2121637 to PB, KL, and JM. Field work was also supported by award G-2016-7206 from the Alfred P. Sloan Foundation and the Deep Carbon Observatory to PB, KL, DG, and JM. Additional support came from The National Fund for Scientific and Technological Development of Chile (FONDECYT) Grant 11191138 (The National Research and Development Agency of Chile, ANID Chile), and COPAS COASTAL ANID FB210021 to GJ. DG was partially supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program Grant Agreement No. 948972—COEVOLVE—ERC-2020-STG

The Bioinformatics Virtual Coordination Network: An open-source and interactive learning environment

Lockdowns and “stay-at-home” orders, starting in March 2020, shuttered bench and field dependent research across the world as a consequence of the global COVID-19 pandemic. The pandemic continues to have an impact on research progress and career development, especially for graduate students and early career researchers, as strict social distance limitations stifle ongoing research and impede in-person educational programs. The goal of the Bioinformatics Virtual Coordination Network (BVCN) was to reduce some of these impacts by helping research biologists learn new skills and initiate computational projects as alternative ways to carry out their research. The BVCN was founded in April 2020, at the peak of initial shutdowns, by an international group of early-career microbiology researchers with expertise in bioinformatics and computational biology. The BVCN instructors identified several foundational bioinformatic topics and organized hands-on tutorials through cloud-based platforms that had minimal hardware requirements (in order to maximize accessibility) such as RStudio Cloud and MyBinder. The major topics included the Unix terminal interface, R and Python programming languages, amplicon analysis, metagenomics, functional protein annotation, transcriptome analysis, network science, and population genetics and comparative genomics. The BVCN was structured as an open-access resource with a central hub providing access to all lesson content and hands-on tutorials (https://biovcnet.github.io/). As laboratories reopened and participants returned to previous commitments, the BVCN evolved: while the platform continues to enable “a la carte” lessons for learning computational skills, new and ongoing collaborative projects were initiated among instructors and participants, including a virtual, open-access bioinformatics conference in June 2021. In this manuscript we discuss the history, successes, and challenges of the BVCN initiative, highlighting how the lessons learned and strategies implemented may be applicable to the development and planning of future courses, workshops, and training programs

Mineralized microbialites as archives of environmental evolution of a hypersaline lake basin: Laguna Negra, Catamarca Province, Argentina

Environmental fluctuations related to climate, biological productivity, and evaporation can be recorded by sedimentary archives within lacustrine depositional systems. Sediments within terminal, closed-basin lakes are amongst the most sensitive paleoenvironmental indicators, and have great potential for permitting detailed reconstruction of environmental conditions via a variety of geochemical and isotopic proxies. Microbialites, however, have been largely overlooked as repositories of paleoenvironmental data. Here, we investigate mineralized microbialites within Laguna Negra, a high-altitude (4100 meters above sea level) hypersaline, closed-basin lake in the Argentinian Puna region and explore the potential recovery of environmental signals from these unique sedimentary archives. Mineralized microbialites within Laguna Negra preserve complex layering composed of three distinct carbonate fabrics—isopachous cement phases, botryoidal precipitates, and microbially-associated micrite. These phases are interpreted to reflect differential physical and biological influences on carbonate nucleation and growth. Detailed preservation of successive laminae within these microbialites provides the opportunity for time-wise reconstruction of geochemical signatures. Geochemical analysis of Laguna Negra microbialites shows overall range of δ13[delta-13]Ccarb[carbonate carbon] is from +5.75‰ [permil] to +18.25‰ and from -2.04‰ to +7.36‰ for δ18[delta-18]Ocarb[carbonate oxygen]. Long-term signals preserved within successive laminae of lighter δ13Ccarb and δ18Ocarb through time suggests increased input water contribution since the beginning of microbialite deposition. General hydrological evolution of Laguna Negra is reconstructed via integration of observed oxygen isotopes signatures with published water balance models, and is consistent with regional records from other lacustrine systems. Examination of paired δ13Ccarb and δ13[delta-13]Corg[organic carbon] permits interpretation of the relative effects of evaporation and biotic activity in the evolution of Laguna Negra, and reveals that extrinsic parameters, such as CO2 [carbon dioxide] degassing and evaporation are the primary control on isotopic evolution. Geochemical and petrographic differences between microbialites across a spatial gradient, however, suggest that Laguna Negra microbialites also preserve signals that represent both heterogeneous evolution of environments within the lake and influence of biogenic activity. Ultimately, understanding of the relative effects of environmental and biotic parameters on the evolution of lacustrine deposits will enhance our understanding of both paleoenvironmental change and its potential relationship to microbialite mineralization

Woeseiales transcriptional response to shallow burial in Arctic fjord surface sediment.

Distinct lineages of Gammaproteobacteria clade Woeseiales are globally distributed in marine sediments, based on metagenomic and 16S rRNA gene analysis. Yet little is known about why they are dominant or their ecological role in Arctic fjord sediments, where glacial retreat is rapidly imposing change. This study combined 16S rRNA gene analysis, metagenome-assembled genomes (MAGs), and genome-resolved metatranscriptomics uncovered the in situ abundance and transcriptional activity of Woeseiales with burial in four shallow sediment sites of Kongsfjorden and Van Keulenfjorden of Svalbard (79°N). We present five novel Woeseiales MAGs and show transcriptional evidence for metabolic plasticity during burial, including sulfur oxidation with reverse dissimilatory sulfite reductase (dsrAB) down to 4 cm depth and nitrite reduction down to 6 cm depth. A single stress protein, spore protein SP21 (hspA), had a tenfold higher mRNA abundance than any other transcript, and was a hundredfold higher on average than other transcripts. At three out of the four sites, SP21 transcript abundance increased with depth, while total mRNA abundance and richness decreased, indicating a shift in investment from metabolism and other cellular processes to build-up of spore protein SP21. The SP21 gene in MAGs was often flanked by genes involved in membrane-associated stress response. The ability of Woeseiales to shift from sulfur oxidation to nitrite reduction with burial into marine sediments with decreasing access to overlying oxic bottom waters, as well as enter into a dormant state dominated by SP21, may account for its ubiquity and high abundance in marine sediments worldwide, including those of the rapidly shifting Arctic

Chemolithoautotroph distributions across the subsurface of a convergent margin

: Subducting oceanic crusts release fluids rich in biologically relevant compounds into the overriding plate, fueling subsurface chemolithoautotrophic ecosystems. To understand the impact of subsurface geochemistry on microbial communities, we collected fluid and sediments from 14 natural springs across a ~200 km transect across the Costa Rican convergent margin and performed shotgun metagenomics. The resulting 404 metagenome-assembled genomes (MAGs) cluster into geologically distinct regions based on MAG abundance patterns: outer forearc-only (25% of total relative abundance), forearc/arc-only (38% of total relative abundance), and delocalized (37% of total relative abundance) clusters. In the outer forearc, Thermodesulfovibrionia, Candidatus Bipolaricaulia, and Firmicutes have hydrogenotrophic sulfate reduction and Wood-Ljungdahl (WL) carbon fixation pathways. In the forearc/arc, Anaerolineae, Ca. Bipolaricaulia, and Thermodesulfovibrionia have sulfur oxidation, nitrogen cycling, microaerophilic respiration, and WL, while Aquificae have aerobic sulfur oxidation and reverse tricarboxylic acid carbon fixation pathway. Transformation-based canonical correspondence analysis shows that MAG distribution corresponds to concentrations of aluminum, iron, nickel, dissolved inorganic carbon, and phosphate. While delocalized MAGs appear surface-derived, the subsurface chemolithoautotrophic, metabolic, and taxonomic landscape varies by the availability of minerals/metals and volcanically derived inorganic carbon. However, the WL pathway persists across all samples, suggesting that this versatile, energy-efficient carbon fixation pathway helps shape convergent margin subsurface ecosystems

The Bioinformatics Virtual Coordination Network: An Open-Source and Interactive Learning Environment

Lockdowns and “stay-at-home” orders, starting in March 2020, shuttered bench and field dependent research across the world as a consequence of the global COVID-19 pandemic. The pandemic continues to have an impact on research progress and career development, especially for graduate students and early career researchers, as strict social distance limitations stifle ongoing research and impede in-person educational programs. The goal of the Bioinformatics Virtual Coordination Network (BVCN) was to reduce some of these impacts by helping research biologists learn new skills and initiate computational projects as alternative ways to carry out their research. The BVCN was founded in April 2020, at the peak of initial shutdowns, by an international group of early-career microbiology researchers with expertise in bioinformatics and computational biology. The BVCN instructors identified several foundational bioinformatic topics and organized hands-on tutorials through cloud-based platforms that had minimal hardware requirements (in order to maximize accessibility) such as RStudio Cloud and MyBinder. The major topics included the Unix terminal interface, R and Python programming languages, amplicon analysis, metagenomics, functional protein annotation, transcriptome analysis, network science, and population genetics and comparative genomics. The BVCN was structured as an open-access resource with a central hub providing access to all lesson content and hands-on tutorials (https://biovcnet.github.io/). As laboratories reopened and participants returned to previous commitments, the BVCN evolved: while the platform continues to enable “a la carte” lessons for learning computational skills, new and ongoing collaborative projects were initiated among instructors and participants, including a virtual, open-access bioinformatics conference in June 2021. In this manuscript we discuss the history, successes, and challenges of the BVCN initiative, highlighting how the lessons learned and strategies implemented may be applicable to the development and planning of future courses, workshops, and training programs

Effect of tectonic processes on biosphere-geosphere feedbacks across a convergent margin

The subsurface is among Earth's largest biomes, but the extent to which microbial communities vary across tectonic plate boundaries or interact with subduction-scale geological processes remains unknown. Here we compare bacterial community composition with deep-subsurface geochemistry from 21 hot springs across the Costa Rican convergent margin. We find that cation and anion compositions of the springs reflect the dip angle and position of the underlying tectonic structure and also correlate with the bacterial community. Co-occurring microbial cliques related to cultured chemolithoautotrophs that use the reverse tricarboxylic acid cycle (rTCA) as well as abundances of metagenomic rTCA genes correlate with concentrations of slab-volatilized carbon. This, combined with carbon isotope evidence, suggests that fixation of slab-derived CO2 into biomass may support a chemolithoautotrophy-based subsurface ecosystem. We calculate that this forearc subsurface biosphere could sequester 1.4 x 10(9) to 1.4 x 10(10) mol of carbon per year, which would decrease estimates of the total carbon delivered to the mantle by 2 to 22%. Based on the observed correlations, we suggest that distribution and composition of the subsurface bacterial community are probably affected by deep tectonic processes across the Costa Rican convergent margin and that, by sequestering carbon volatilized during subduction, these chemolithoautotrophic communities could in turn impact the geosphere