• Energy Research

Picoeukaryotes are a taxonomically diverse group of organisms less than 2 micrometers in diameter. Photosynthetic marine picoeukaryotes in the genus Micromonas thrive in ecosystems ranging from tropical to polar and could serve as sentinel organisms for biogeochemical fluxes of modern oceans during climate change. These broadly distributed primary producers belong to an anciently diverged sister clade to land plants. Although Micromonas isolates have high 18 S ribosomal RNA gene identity, we found that genomes from two isolates shared only 90% of their predicted genes. Their independent evolutionary paths were emphasized by distinct riboswitch arrangements as well as the discovery of intronic repeat elements in one isolate, and in metagenomic data, but not in other genomes. Divergence appears to have been facilitated by selection and acquisition processes that actively shape the repertoire of genes that are mutually exclusive between the two isolates differently than the core genes. Analyses of the Micromonas genomes offer valuable insights into ecological differentiation and the dynamic nature of early plant evolution.

Municipal wastewater (WW), if not properly remediated, poses a threat to the environment and human health by carrying significant loads of nutrients and pathogens. These contaminants pollute rivers, lakes, and natural reservoirs where they cause eutrophication and pathogen-mediated diseases. However, the high nutrient content of WW makes it an ideal environment for remediation with microalgae that require high nutrient concentrations for growth and are not susceptible to toxins and pathogens. Given that an appropriate algal strain is used for remediation, the incurred biomass can be refined for the production of biofuel. Four microalgal species (Chlamydomonas reinhardtii, Chlorella sp., Parachlorella kessleri-I, and Nannochloropsis gaditana) were screened for efficient phycoremediation of municipal WW and potential use for biodiesel production. Among the four strains tested, P. kessleri-I showed the highest growth rate and biomass production in 100% WW. It efficiently removed all major nutrients with a removal rate of up to 98% for phosphate after 10 days of growth in 100% municipal WW collected from Delhi. The growth of P. kessleri-I in WW resulted in a 50% increase of biomass and a 115% increase of lipid yield in comparison to growth in control media. The Fatty acid methyl ester (FAME), and fuel properties of lipids isolated from cells grown in WW complied with international standards. The present study provides evidence that the green alga P. kessleri-I effectively remediates municipal WW and can be used to produce biodiesel.

Diatoms, a key group of polar marine microbes, support highly productive ocean ecosystems. Like all life on earth, diatoms do not live in isolation, and they are therefore under constant biotic and abiotic pressures which directly influence their evolution through natural selection. Despite their importance in polar ecosystems, polar diatoms are understudied compared to temperate species. The observed rapid change in the polar climate, especially warming, has created increased research interest to discover the underlying causes and potential consequences on single species to entire ecosystems. Next-Generation Sequencing (NGS) technologies have greatly expanded our knowledge by revealing the molecular underpinnings of physiological adaptations to polar environmental conditions. Their genomes, transcriptomes, and proteomes together with the first eukaryotic meta-omics data of surface ocean polar microbiomes reflect the environmental pressures through adaptive responses such as the expansion of protein families over time as a consequence of selection. Polar regions and their microbiomes are inherently connected to climate cycles and their feedback loops. An integrated understanding built on “omics” resources centered around diatoms as key primary producers will enable us to reveal unifying concepts of microbial co-evolution and adaptation in polar oceans. This knowledge, which aims to relate past environmental changes to specific adaptations, will be required to improve climate prediction models for polar ecosystems because it provides a unifying framework of how interacting and co-evolving biological communities might respond to future environmental change.

AbstractKelp are main iodine accumulators in the ocean, and their growth and photosynthesis are likely to benefit from elevated seawater CO2 levels due to ocean acidification. However, there are currently no data on the effects of ocean acidification on iodine metabolism in kelp. As key primary producers in coastal ecosystems worldwide, any change in their iodine metabolism caused by climate change will potentially have important consequences for global geochemical cycles of iodine, including iodine levels of coastal food webs that underpin the nutrition of billions of humans around the world. Here, we found that elevated pCO2 enhanced growth and increased iodine accumulation not only in the model kelp Saccharina japonica using both short‐term laboratory experiment and long‐term in situ mesocosms, but also in several other edible and ecologically significant seaweeds using long‐term in situ mesocosms. Transcriptomic and proteomic analysis of S. japonica revealed that most vanadium‐dependent haloperoxidase genes involved in iodine efflux during oxidative stress are down‐regulated under increasing pCO2, suggesting that ocean acidification alleviates oxidative stress in kelp, which might contribute to their enhanced growth. When consumed by abalone (Haliotis discus), elevated iodine concentrations in S. japonica caused increased iodine accumulation in abalone, accompanied by reduced synthesis of thyroid hormones. Thus, our results suggest that kelp will benefit from ocean acidification by a reduction in environmental stress however; iodine levels, in kelp‐based coastal food webs will increase, with potential impacts on biogeochemical cycles of iodine in coastal ecosystems.

AbstractEukaryotic phytoplankton are responsible for at least 20% of annual global carbon fixation. Their diversity and activity are shaped by interactions with prokaryotes as part of complex microbiomes. Although differences in their local species diversity have been estimated, we still have a limited understanding of environmental conditions responsible for compositional differences between local species communities on a large scale from pole to pole. Here, we show, based on pole-to-pole phytoplankton metatranscriptomes and microbial rDNA sequencing, that environmental differences between polar and non-polar upper oceans most strongly impact the large-scale spatial pattern of biodiversity and gene activity in algal microbiomes. The geographic differentiation of co-occurring microbes in algal microbiomes can be well explained by the latitudinal temperature gradient and associated break points in their beta diversity, with an average breakpoint at 14 °C ± 4.3, separating cold and warm upper oceans. As global warming impacts upper ocean temperatures, we project that break points of beta diversity move markedly pole-wards. Hence, abrupt regime shifts in algal microbiomes could be caused by anthropogenic climate change.

AbstractMicrobial rhodopsins are photoreceptor proteins that convert light into biological signals or energy. Proteins of the xanthorhodopsin family are common in eukaryotic photosynthetic plankton including diatoms. However, their biological role in these organisms remains elusive. Here we report on a xanthorhodopsin variant (FcR1) isolated from the polar diatom Fragilariopsis cylindrus. Applying a combination of biophysical, biochemical and reverse genetics approaches, we demonstrate that FcR1 is a plastid-localized proton pump which binds the chromophore retinal and is activated by green light. Enhanced growth of a Thalassiora pseudonana gain-of-function mutant expressing FcR1 under iron limitation shows that the xanthorhodopsin proton pump supports growth when chlorophyll-based photosynthesis is iron-limited. The abundance of xanthorhodopsin transcripts in natural diatom communities of the surface oceans is anticorrelated with the availability of dissolved iron. Thus, we propose that these proton pumps convey a fitness advantage in regions where phytoplankton growth is limited by the availability of dissolved iron.