The microbiome of the canopy-forming kelps, Nereocystis and Macrocystis, from the outer Olympic Coast to the Puget Sound

Canopy-forming kelps create vast underwater forests that are among the most productive marine ecosystems. In addition to providing vital habitat for macroscopic organisms, kelps also host an abundant microbial community in their surface mucus layer. In the Salish Sea, two canopy-forming kelps with contrasting life histories co-occur; Macrocystis pyrifera, a perennial species, and Nereocystis luetkeana, an annual species. Kelp-associated microbial communities were sampled along a spatial gradient, including sites from the outer Olympic Coast, Strait of Juan de Fuca, and Puget Sound. We characterized the microbial communities associated with each kelp species and the surrounding seawater using next-generation Illumina sequencing of 16S rRNA genes. Our preliminary results show that canopy-forming kelps host complex microbial symbiont communities that are host-specific and distinct from free-living bacteria in the surrounding seawater. Based on fluorescence microscopy data, up to 25 million bacteria live on just one square centimeter of N. luetkeana tissue. In addition to examining spatial variation in the kelp microbiome, we examined the impact of N. luetkeana and M. pyrifera kelp forests on the surrounding seawater chemistry. We used an enriched carbon stable isotope tracer experiment (13C-bicarbonate) to demonstrate simultaneous carbon fixation and dissolved organic carbon (DOC) production by N. luetkeana from Tatoosh Island, WA. During the daytime, carbon fixed by N. luetkeana is leaked into the surrounding seawater at a rate of 10 μmol DOC per hour per gram of dry mass. This carbon presents an abundant food resource for heterotrophic microbes in the surrounding seawater. Given the immense surface area of kelp forests, the kelp microbiome has potentially far-reaching impacts on kelp forest productivity and coastal nutrient cycling

Successional Dynamics and Seascape-Level Patterns of Microbial Communities on the Canopy-Forming Kelps Nereocystis luetkeana and Macrocystis pyrifera

Canopy-forming kelps create underwater forests that are among the most productive marine ecosystems. On the Pacific coast of North America, two canopy-forming kelps with contrasting life histories co-occur; Macrocystis pyrifera, a perennial species, and Nereocystis luetkeana, an annual species. Kelp blade-associated microbes were sampled from 12 locations across a spatial gradient in Washington, United States, from the outer Pacific Coast to Puget Sound. Microbial communities were characterized using next-generation Illumina sequencing of 16S rRNA genes. At higher taxonomic levels (bacterial phylum and class), canopy-forming kelps hosted remarkably similar microbial communities, but at the amplicon sequence variant level, microbial communities on M. pyrifera and N. luetkeana were host-specific and distinct from free-living bacteria in the surrounding seawater. Microbial communities associated with blades of each kelp species displayed significant geographic variation. The microbiome of N. luetkeana changed along the spatial gradient and was significantly correlated to salinity, with outer Pacific coast sites enriched in Bacteroidetes (family Saprospiraceae) and Gammaproteobacteria (Granulosicoccus sp.), and southern Puget Sound sites enriched in Alphaproteobacteria (family Hyphomonadaceae). We also examined microbial community development and succession on meristematic and apical N. luetkeana blade tissues throughout the summer growing season on Tatoosh Island, WA. Across all dates, microbial communities were less diverse on younger, meristematic blade tissue compared to the older, apical tissues. In addition, phylogenetic relatedness among microbial taxa increased from meristematic to apical blade tissues, suggesting that the addition of microbial taxa to the community was a non-random process that selected for certain phylogenetic groups of microbes. Microbial communities on older, apical tissues displayed significant temporal variation throughout the summer and microbial taxa that were differentially abundant over time displayed clear patterns of community succession. Overall, we report that host species identity, geographic location, and blade tissue age shape the microbial communities on canopy-forming kelps

Spatial organization of the kelp microbiome at micron scales

Background: Elucidating the spatial structure of host-associated microbial communities is essential for understanding taxon-taxon interactions within the microbiota and between microbiota and host. Macroalgae are colonized by complex microbial communities, suggesting intimate symbioses that likely play key roles in both macroalgal and bacterial biology, yet little is known about the spatial organization of microbes associated with macroalgae. Canopy-forming kelp are ecologically significant, fixing teragrams of carbon per year in coastal kelp forest ecosystems. We characterized the micron-scale spatial organization of bacterial communities on blades of the kelp Nereocystis luetkeana using fluorescence in situ hybridization and spectral imaging with a probe set combining phylum-, class-, and genus-level probes to localize and identify > 90% of the microbial community. Results: We show that kelp blades host a dense microbial biofilm composed of disparate microbial taxa in close contact with one another. The biofilm is spatially differentiated, with clustered cells of the dominant symbiont Granulosicoccus sp. (Gammaproteobacteria) close to the kelp surface and filamentous Bacteroidetes and Alphaproteobacteria relatively more abundant near the biofilm-seawater interface. A community rich in Bacteroidetes colonized the interior of kelp tissues. Microbial cell density increased markedly along the length of the kelp blade, from sparse microbial colonization of newly produced tissues at the meristematic base of the blade to an abundant microbial biofilm on older tissues at the blade tip. Kelp from a declining population hosted fewer microbial cells compared to kelp from a stable population. Conclusions: Imaging revealed close association, at micrometer scales, of different microbial taxa with one another and with the host. This spatial organization creates the conditions necessary for metabolic exchange among microbes and between host and microbiota, such as provisioning of organic carbon to the microbiota and impacts of microbial nitrogen metabolisms on host kelp. The biofilm coating the surface of the kelp blade is well-positioned to mediate interactions between the host and surrounding organisms and to modulate the chemistry of the surrounding water column. The high density of microbial cells on kelp blades (10(5)-10(7) cells/cm(2)), combined with the immense surface area of kelp forests, indicates that biogeochemical functions of the kelp microbiome may play an important role in coastal ecosystems

Interactive effects of temperature and nitrogen on the physiology of kelps (Nereocystis luetkeana and Saccharina latissima)

Kelp forest declines have been linked to warming ocean temperatures worldwide. Ocean warming rarely occurs in isolation, so multiple stressor studies are necessary to understand the physiological responses of kelp to climate change. The canopy-forming bull kelp, Nereocystis luetkeana, is going locally extinct in areas of the Salish Sea that are seasonally warm and nutrient poor, while the understory kelp, Saccharina latissima, persists at those sites. Further, nitrogen availability can alter physiological responses of kelps to temperature stress, including alleviating warming stress. We compared the physiological responses of kelp sporophytes to high temperature stress and nitrogen limitation between two populations of N. luetkeana with different environmental histories (warm and nutrient poor vs. cold and nutrient rich) and between two species, N. luetkeana and S. latissima. Using laboratory mesocosms, we tested the interactive effects of short term (8-9 day) exposure of kelp blades to different temperatures: low (9, 13°C), moderate (15, 16°C), and warm (21°C) at two different nitrogen concentrations: low (1-3 μM) vs. high (>10 μM). We examined a wide array of physiological responses: blade growth, photosynthesis, respiration, photosynthetic yield, nutrient uptake, and tissue C:N. Both kelp species responded negatively to elevated temperatures, but not to low nitrogen levels. Blades of both species showed signs of metabolic stress and reduced growth in the warmest temperature treatment (21°C), at both high and low nitrogen levels, suggesting that N. luetkeana and S. latissima are susceptible to thermal stress over short time periods. Populations of N. luetkeana from warm, nutrient poor and cool, nutrient rich areas were equally susceptible to the effects of ocean warming. Our results suggest that nutrient additions may actually reduce kelp performance at supra-optimal temperatures, and a thorough understanding of kelp responses to coastal temperature and nutrient dynamics is needed to guide conservation and restoration actions

Promoting inclusive metrics of success and impact to dismantle a discriminatory reward system in science

“The most dangerous phrase in the language is: We’ve always done it this way.” —Rear Admiral Grace HopperSuccess and impact metrics in science are based on a system that perpetuates sexist and racist “rewards” by prioritizing citations and impact factors. These metrics are flawed and biased against already marginalized groups and fail to accurately capture the breadth of individuals’ meaningful scientific impacts. We advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion. We outline pathways for a paradigm shift in scientific values based on multidimensional mentorship and promoting mentee well-being. These actions will require collective efforts supported by academic leaders and administrators to drive essential systemic change.Peer reviewe

Invertebrate grazing and epilithon assemblages control benthic nitrogen fixation in an N-limited river network

The effects of top-down (e.g., herbivory) and bottom-up (e.g., nutrient supply) processes on primary producers are often interdependent. In stream ecosystems, interactions between herbivorous grazers and physical factors, such as light and temperature, can alter the abundance and taxonomic composition of epilithic nitrogen (N) fixers. To examine how grazing and physical factors mediate the source ofNto stream ecosystems, we conducted an in-situ grazer exclusion experiment by removing crawling invertebrate grazers from epilithon-covered rocks in 3 streams with varying drainage areas, representing a gradient of temperature and light levels, within a northern California river network. After ∼1mo of grazer exclusion, we measured epilithon biomass and composition,N2 fixation, and ammonium (NH4), nitrate (NO3), and phosphate (PO4) uptake rates. Epilithic biomass, N2-fixation rates, and N and phosphorus uptake rates differed among the 3 streams, and rates were highest in the largest, open-canopy stream. Increases in N2-fixation rates with stream size were due to higher nitrogenase activity per unit of biomass as well as higher absolute biomass of N2 fixers. The presence of grazers interacted with physical factors to control nutrient fluxes. Ecologically-significant grazer removal effects only occurred in the largest stream, where grazing increased the influx of atmospheric N2 to the benthic biofilm. N2-fixation rates increased with grazing while NH4 uptake rates decreased by a similar proportion, shifting the predominant N source from the assimilation of dissolved N to atmospheric N2 via fixation by cyanobacteria. By altering the balance between N2 fixation and water column N uptake, grazers can mediate the flux of N to stream ecosystems

Functional Insights into the Kelp Microbiome from Metagenome-Assembled Genomes

Eukaryotic organisms evolved in a microbial world and often have intimate associations with diverse bacterial groups. Kelp, brown macroalgae in the order Laminariales, play a vital role in coastal ecosystems, yet we know little about the functional role of the microbial symbionts that cover their photosynthetic surfaces. Here, we reconstructed 79 bacterial metagenome-assembled genomes (MAGs) from blades of the bull kelp, Nereocystis luetkeana, allowing us to determine their metabolic potential and functional roles. Despite the annual life history of bull kelp, nearly half of the bacterial MAGs were detected across multiple years. Diverse members of the kelp microbiome, spanning 6 bacterial phyla, contained genes for transporting and assimilating dissolved organic matter (DOM), which is secreted by kelp in large quantities and likely fuels the metabolism of these heterotrophic bacteria. Bacterial genomes also contained alginate lyase and biosynthesis genes, involved in polysaccharide degradation and biofilm formation, respectively. Kelp-associated bacterial genomes contained genes for dissimilatory nitrate reduction and urea hydrolysis, likely providing a reduced source of nitrogen to the host kelp. The genome of the most abundant member of the kelp microbiome and common macroalgal symbiont, Granulosicoccus, contained a full suite of genes for synthesizing cobalamin (vitamin B12), suggesting that kelp-associated bacteria have the potential to provide their host kelp with vitamins. Finally, kelp-associated Granulosicoccus contained genes that typify the aerobic anoxygenic phototrophic bacteria, including genes for bacteriochlorophyll synthesis and photosystem II reaction center proteins, making them the first known photoheterotrophic representatives of this genus

Symptoms and health problems in pregnancy and their association with social factors, smoking, alcohol and caffeine intake and attitude to pregnancy

Summary. This paper describes the prevalence and correlates of symptoms and health problems in pregnancy using data from a prospective population study in London. Data on the prevalence of 11 symptoms and 12 health problems were obtained at three points in pregnancy from a consecutive sample of 1513 white women. Relationships were examined between these symptoms and a range of psychosocial factors including social class, education, marital status, income, smoking, alcohol, caffeine, attitude to pregnancy and whether the pregnancy was planned.Most women reported nausea and breast tenderness in early pregnancy. Heartburn, backache, constipation and headaches were also common. The prevalence of symptoms tended to increase with gestation except for nausea and vomiting. Women with manual occupations, minimum education, low income, single marital status and unplanned pregnancy reported more of most symptoms except nausea which was associated with higher social status. A negative attitude to pregnancy was associated with more headaches but was unrelated to nausea. Women who smoked reported more 'nerves and depression' but less nausea. In general, nausea and vomiting showed a different pattern of associations from all other symptoms

Promoting inclusive metrics of success and impact to dismantle a discriminatory reward system in science

Success and impact metrics in science are based on a system that perpetuates sexist and racist “rewards” by prioritizing citations and impact factors. These metrics are flawed and biased against already marginalized groups and fail to accurately capture the breadth of individuals’ meaningful scientific impacts. We advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion. We outline pathways for a paradigm shift in scientific values based on multidimensional mentorship and promoting mentee well-being. These actions will require collective efforts supported by academic leaders and administrators to drive essential systemic change.</p

Promoting inclusive metrics of success and impact to dismantle a discriminatory reward system in science.

Success and impact metrics in science are based on a system that perpetuates sexist and racist "rewards" by prioritizing citations and impact factors. These metrics are flawed and biased against already marginalized groups and fail to accurately capture the breadth of individuals' meaningful scientific impacts. We advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion. We outline pathways for a paradigm shift in scientific values based on multidimensional mentorship and promoting mentee well-being. These actions will require collective efforts supported by academic leaders and administrators to drive essential systemic change