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Abstract Biological dinitrogen (N2) fixation supplies nitrogen to the oceans, supporting primary productivity, and is carried out by some bacteria and archaea referred to as diazotrophs. Cyanobacteria are conventionally considered to be the major contributors to marine N2 fixation, but non-cyanobacterial diazotrophs (NCDs) have been shown to be distributed throughout ocean ecosystems. However, the biogeochemical significance of marine NCDs has not been demonstrated. This review synthesizes multiple datasets, drawing from cultivation-independent molecular techniques and data from extensive oceanic expeditions, to provide a comprehensive view into the diversity, biogeography, ecophysiology, and activity of marine NCDs. A NCD nifH gene catalog was compiled containing sequences from both PCR-based and PCR-free methods, identifying taxa for future studies. NCD abundances from a novel database of NCD nifH-based abundances were colocalized with environmental data, unveiling distinct distributions and environmental drivers of individual taxa. Mechanisms that NCDs may use to fuel and regulate N2 fixation in response to oxygen and fixed nitrogen availability are discussed, based on a metabolic analysis of recently available Tara Oceans expedition data. The integration of multiple datasets provides a new perspective that enhances understanding of the biology, ecology, and biogeography of marine NCDs and provides tools and directions for future research. The authors discuss recent advances that highlight marine non-cyanobacterial diazotrophs in marine ecosystems, with a focus on diversity, drivers of their global biogeography and potential ecophysiologies, and their significance to the nitrogen cycle in well-lit oxygenated euphotic waters.

The anaerobic formation and oxidation of methane involve unique enzymatic mechanisms and cofactors, all of which are believed to be specific for C 1 -compounds. Here we show that an anaerobic thermophilic enrichment culture composed of dense consortia of archaea and bacteria apparently uses partly similar pathways to oxidize the C 4 hydrocarbon butane. The archaea, proposed genus ‘ Candidatus Syntrophoarchaeum’, show the characteristic autofluorescence of methanogens, and contain highly expressed genes encoding enzymes similar to methyl-coenzyme M reductase. We detect butyl-coenzyme M, indicating archaeal butane activation analogous to the first step in anaerobic methane oxidation. In addition, Ca . Syntrophoarchaeum expresses the genes encoding β-oxidation enzymes, carbon monoxide dehydrogenase and reversible C 1 methanogenesis enzymes. This allows for the complete oxidation of butane. Reducing equivalents are seemingly channelled to HotSeep-1, a thermophilic sulfate-reducing partner bacterium known from the anaerobic oxidation of methane. Genes encoding 16S rRNA and methyl-coenzyme M reductase similar to those identifying Ca . Syntrophoarchaeum were repeatedly retrieved from marine subsurface sediments, suggesting that the presented activation mechanism is naturally widespread in the anaerobic oxidation of short-chain hydrocarbons. Anaerobic archaea enriched in thermophilic microbial consortia completely degrade butane by modifying mechanisms which were hitherto thought to be specific to methane metabolism. Environmental oxidation of non-methane hydrocarbons Research on the anaerobic oxidation of natural gas has largely been focused on methane as the most abundant constituent. It is less clear how short-chain alkanes—including ethane, propane, n -butane and iso -butane, which together make up about 20% of natural gas—are anaerobically metabolized. Sulfate-reducing bacteria are the only organisms known to date to anaerobically oxidize short-chain hydrocarbons. Gunter Wegener and colleagues identify an anaerobic thermophilic enrichment culture composed of dense consortia of archaea and bacteria that uses a pathway similar to anaerobic methane oxidation, which was previously thought to be specific for C 1 -compounds, to oxidize butane. Archaea activate butane, and reducing equivalents are channelled to sulfate-reducing partner bacteria. Similar consortia are detected in marine subsurface sediments, suggesting that this pathway may be widespread in nature.

Biological nitrogen fixation is a major important source of nitrogen for low-nutrient surface oceanic waters. Nitrogen-fixing (diazotrophic) cyanobacteria are believed to be the primary contributors to this process, but the contribution of non-cyanobacterial diazotrophic organisms in oxygenated surface water, while hypothesized to be important, has yet to be demonstrated. In this study, we used simultaneous 15 N-dinitrogen and 13 C-bicarbonate incubations combined with nanoscale secondary ion mass spectrometry analysis to screen tens of thousands of mostly particle-associated, cell-like regions of interest collected from the North Pacific Subtropical Gyre. These dual isotope incubations allow us to distinguish between non-cyanobacterial and cyanobacterial nitrogen-fixing microorganisms and to measure putative cell-specific nitrogen fixation rates. With this approach, we detect nitrogen fixation by putative non-cyanobacterial diazotrophs in the oxygenated surface ocean, which are associated with organic-rich particles (<210 µm size fraction) at two out of seven locations sampled. When present, up to 4.1% of the analyzed particles contain at least one active putative non-cyanobacterial diazotroph. The putative non-cyanobacterial diazotroph nitrogen fixation rates (0.76 ± 1.60 fmol N cell −1 d −1 ) suggest that these organisms are capable of fixing dinitrogen in oxygenated surface water, at least when attached to particles, and may contribute to oceanic nitrogen fixation. Nitrogen-fixing (diazotrophic) cyanobacteria provide a critical nutrient input to the ocean. Non-cyanobacterial diazotrophs are also thought to contribute, but they have not been observed to fix nitrogen. Using dual isotope labeling combined with nanoscale secondary ion mass spectrometry, this study demonstrates that putative non-cyanobacterial diazotrophs attached to particles can fix nitrogen.

Biological dinitrogen (N₂) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N₂-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N₂ uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N₂ in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N₂ fixation is not constrained to subtropical waters, challenging paradigms and models of global N₂ fixation. The Arctic is particularly sensitive to climate change, and N₂ fixation may increase in Arctic waters under future climate scenarios.

The microbial fixation of N 2 is the largest source of biologically available nitrogen (N) to the oceans. However, it is the most energetically expensive N-acquisition process and is believed inhibited when less energetically expensive forms, like dissolved inorganic N (DIN), are available. Curiously, the cosmopolitan N 2 -fixing UCYN-A/haptophyte symbiosis grows in DIN-replete waters, but the sensitivity of their N 2 fixation to DIN is unknown. We used stable isotope incubations, catalyzed reporter deposition fluorescence in-situ hybridization (CARD-FISH), and nanoscale secondary ion mass spectrometry (nanoSIMS), to investigate the N source used by the haptophyte host and sensitivity of UCYN-A N 2 fixation in DIN-replete waters. We demonstrate that under our experimental conditions, the haptophyte hosts of two UCYN-A sublineages do not assimilate nitrate (NO 3 − ) and meet little of their N demands via ammonium (NH 4 + ) uptake. Instead the UCYN-A/haptophyte symbiosis relies on UCYN-A N 2 fixation to supply large portions of the haptophyte’s N requirements, even under DIN-replete conditions. Furthermore, UCYN-A N 2 fixation rates, and haptophyte host carbon fixation rates, were at times stimulated by NO 3 − additions in N-limited waters suggesting a link between the activities of the bulk phytoplankton assemblage and the UCYN-A/haptophyte symbiosis. The results suggest N 2 fixation may be an evolutionarily viable strategy for diazotroph–eukaryote symbioses, even in N-rich coastal or high latitude waters.

To investigate the important supportive microorganisms responsible for trichloroethene (TCE) bioremediation under specific environmental conditions and their relationship with Dehalococcoides (Dhc), four stable and robust enrichment cultures were generated using contaminated groundwater. Enrichments were maintained under four different conditions exploring two parameters: high and low TCE amendments (resulting in inhibited and uninhibited methanogenic activity, respectively) and with and without vitamin B 12 amendment. Lactate was supplied as the electron donor. All enrichments were capable of reductively dechlorinating TCE to vinyl chloride and ethene. The dechlorination rate and ethene generation were higher, and the proportion of electrons used for dechlorination increased when methanogenesis was inhibited. Biologically significant cobalamin biosynthesis was detected in the enrichments without B 12 amendment. Comparative genomics using a genus-wide microarray revealed a Dhc genome similar to that of strain 195 in all enrichments, a strain that lacks the major upstream corrin ring biosynthesis pathway. Seven other bacterial operational taxonomic units (OTUs) were detected using clone libraries. OTUs closest to Pelosinus , Dendrosporobacter , and Sporotalea (PDS) were most dominant. The Clostridium -like OTU was most affected by B 12 amendment and active methanogenesis. Principal component analysis revealed that active methanogenesis, rather than vitamin B 12 limitation, exerted a greater effect on the community structures even though methanogens did not seem to play an essential role in providing corrinoids to Dhc. In contrast, acetogenic bacteria that were abundant in the enrichments, such as PDS and Clostridium sp., may be potential corrinoid providers for Dhc.

As librarians whose roles focus on teaching, we aim to provide meaningful and equitable learning experiences for all students, including students with disabilities. However, as is the case for many librarians, there is an overwhelmingly one-time nature to our interactions with students. Our instruction sessions are usually “one-shots” and, while in our research consultations we may see some students repeatedly, most often we will only see them once or twice in a semester. The often-one-time nature of our work means that we have limited information about the needs of our students, and few opportunities to meaningfully assess students’ learning experiences. As such, it is challenging to determine how accessible our teaching is, both in the classroom and in our research consultations.

Nutrient availability affects primary productivity, and nitrogen (N) is the limiting nutrient over large regions of the ocean. Biological N fixation (BNF) is the conversion of atmospheric dinitrogen (N2) to bioavailable forms of N (ammonium and amino acids). A select group of Bacteria and Archaea, known as diazotrophs, are the only organisms capable of this conversion. BNF is a critical source of N in nutrient-depleted (oligotrophic) marine waters. As such, BNF studies are a fundamental component for better understanding primary productivity and carbon cycling, as well as parameterizing predictive future global ocean models. Unicellular diazotrophs are widespread in marine systems and, in some cases, important contributors of BNF. This dissertation investigates unicellular diazotrophs at the single-cell level, including UCYN-A, a cyanobacterial diazotroph that lives in symbiosis with an algal host, non-cyanobacterial diazotrophs (NCDs), which are putative heterotrophs, and a specific NCD known as Gamma A, which is a commonly occurring organism throughout the tropics and subtropics that belongs to the class Gammaproteobacteria. The single-cell investigations used in these studies can provide high-resolution insights that are not possible from community-level analyses of BNF, such as the N2 fixation rate of individual cells and cell morphology. Single-cell nanoscale secondary ion mass spectrometry (nanoSIMS) analyses were used in chapters 2 and 3 to investigate the cell-specific N2 fixation rates of UCYN-A in the cold waters of the Bering and Arctic Seas where N2 fixation was not previously believed to be possible (chapter 2), and NCDs in the North Pacific Subtropical Gyre where we demonstrated the first direct evidence of NCD N2 fixation on open ocean particles (chapter 3). Chapter 4 focused on a specific uncultivated NCD, Gamma A, using geneFISH to visualize single cells in natural seawater samples. We successfully identified Gamma A cells by developing a fluorescent in situ hybridization (FISH) probe targeting the diazotrophic functional marker gene nifH, revealing Gamma A cells are most often attached to particles. Together these studies provide new insights into the distributions, activities, and physiologies of geographically widespread, unicellular diazotrophs, thus improving our understanding of their roles as sources of fixed N in the surface ocean.

Technical standards are a vital source of information for providing guidelines during the design, manufacture, testing, and use of whole products, materials, and components. To prepare students—especially engineering students—for the workforce, universities are increasing the use of standards within the curriculum. Employers believe it is important for recent university graduates to be familiar with standards. Despite the critical role standards play within academia and the workforce, little information is available on the development of standards information literacy, which includes the ability to understand the standardization process; identify types of standards; and locate, evaluate, and use standards effectively. Libraries and librarians are a critical part of standards education, and much of the discussion has been focused on the curation of standards within libraries. However, librarians also have substantial experience in developing and teaching standards information literacy curriculum. With the need for universities to develop a workforce that is well-educated on the use of standards, librarians and course instructors can apply their experiences in information literacy toward teaching students the knowledge and skills regarding standards that they will need to be successful in their field. This title provides background information for librarians on technical standards as well as collection development best practices. It also creates a model for librarians and course instructors to use when building a standards information literacy curriculum.

Technical standards are a vital source of information for providing guidelines during the design, manufacture, testing, and use of whole products, materials, and components. To prepare students—especially engineering students—for the workforce, universities are increasing the use of standards within the curriculum. Employers believe it is important for recent university graduates to be familiar with standards. Despite the critical role standards play within academia and the workforce, little information is available on the development of standards information literacy, which includes the ability to understand the standardization process; identify types of standards; and locate, evaluate, and use standards effectively. Libraries and librarians are a critical part of standards education, and much of the discussion has been focused on the curation of standards within libraries. However, librarians also have substantial experience in developing and teaching standards information literacy curriculum. With the need for universities to develop a workforce that is well-educated on the use of standards, librarians and course instructors can apply their experiences in information literacy toward teaching students the knowledge and skills regarding standards that they will need to be successful in their field. This title provides background information for librarians on technical standards as well as collection development best practices. It also creates a model for librarians and course instructors to use when building a standards information literacy curriculum.