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Natural and oil surface slicks are widespread phenomena at the air-water interface and represent visible surface films with distinct physicochemical and biological properties compared to non-slick surface films and underlying marine water. Both types of slicks have major functions in nourishing and dispersing surface-dwelling micro- and macroorganisms, contribute to particle generation and carbon cycling, and are known to accumulate pollutants. Despite these functions and the high frequency of slicks in the marine environment, slicks are little understood considering their microbial inhabitants and contributions of these organisms for natural and oil slick establishment, function, and ecology. Our mini review summarizes the current knowledge of microbial life in natural slicks, natural and anthropogenic oil slicks, including the major knowledge gaps and perspectives for future research. Overall, we aim for an increased awareness about the existence of natural slicks, the differentiation between natural and anthropogenic oil slicks and an improved reporting of slick events during sampling of surface film and seawater from the epipelagic zone.

In almost all respiratory organisms, organic substrates are degraded via catabolic processes to the central metabolite acetyl-CoA which is then oxidized to CO 2 for energy metabolism or used as a building block for anabolism. Most microorganisms have either the closed tricarboxylic acid cycle or the complete Wood-Ljungdahl-pathway for acetyl-CoA oxidation, but the sulfate-reducing, naphthalene-degrading culture N47 possesses both completely. Combining 13 C- labeled substrates and mass-specific GC-MS analysis of amino acids and fatty acids with enzyme activity assays suggests that N47 has a chemoorganoautotrophic metabolism degrading complex organic substrates such as naphthalene. Surprisingly, however, the biomass is mainly produced from acetyl-CoA generated de novo via CO 2 -fixation. This metabolism probably requires both a complete Wood-Ljungdahl pathway for acetyl-CoA oxidation and a reverse tricarboxylic acid cycle for CO 2 fixation. Based on genome analysis, this chemoorganoautotrophic metabolism seems to also occur in other sulfate-reducers and anaerobic ammonium-oxidizers.

Abstract It is widely assumed that a taxonomic core community emerges among microbial communities from similar habitats because similar environments select for the same taxa bearing the same traits. Yet, a core community itself is no indicator of selection because it may also arise from dispersal and neutral drift, i.e. by chance. Here, we hypothesize that a core community produced by either selection or chance processes should be distinguishable. While dispersal and drift should produce core communities with similar relative taxon abundances, especially when the proportional core community, i.e. the sum of the relative abundances of the core taxa, is large, selection may produce variable relative abundances. We analyzed the core community of 16S rRNA gene sequences of 193 microbial communities occurring in tiny water droplets enclosed in heavy oil from the Pitch Lake, Trinidad and Tobago. These communities revealed highly variable relative abundances along with a large proportional core community (68.0 ± 19.9%). A dispersal-drift null model predicted a negative relationship of proportional core community and compositional variability along a range of dispersal probabilities and was largely inconsistent with the observed data, suggesting a major role of selection for shaping the water droplet communities in the Pitch Lake. Analysis of microbial communities in tiny water droplets enclosed in oil allows to infer underlying community assembly processes of the taxonomic core community.

ABSTRACT Microbial degradation influences the quality of oil resources. The environmental factors that shape the composition of oil microbial communities are largely unknown because most samples from oil fields are impacted by anthropogenic oil production, perturbing the native ecosystem with exogenous fluids and microorganisms. We investigated the relationship between formation water geochemistry and microbial community composition in undisturbed oil samples. We isolated 43 microliter-sized water droplets naturally enclosed in the heavy oil of the Pitch Lake, Trinidad and Tobago. The water chemistry and microbial community composition within the same water droplet were determined by ion chromatography and 16S rRNA gene amplicon sequencing, respectively. The results revealed a high variability in ion concentrations and community composition between water droplets. Microbial community composition was mostly affected by the chloride concentration, which ranged from freshwater to brackish-sea water. Remarkably, microbial communities did not respond gradually to increasing chloride concentration but showed a sudden change to less diverse and uneven communities when exceeding a chloride concentration of 57.3 mM. The results reveal a threshold-regulated response of microbial communities to salinity, offering new insights into the microbial ecology of oil reservoirs. Microbial communities from Pitch Lake oil show a sudden threshold-regulated response to salinity, leading to less diverse and uneven communities

Anthropogenic carbon dioxide (CO₂) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO₂ in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO₂ (mean ± SD pCO₂ = 1823 ± 161 μatm and pHT = 7.46 ± 0.05) versus in situ CO₂ (504 ± 42 μatm, 7.95 ± 0.04) seawater on the community composition of marine planktonic eukaryotes after 3 and 48 h of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Increased CO₂ significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers, although the chlorophyll a concentration remained constant. OA effects on eukaryotes were consistent between total (DNA-based) and active (cDNA-based) taxa after 48 h, e.g. for the diatoms Trieres chinensis and Stephanopyxis turris. Effects of OA on the relative abundances of OTUs were often species- or even ecotype-specific, and the incubation selectively allowed for detection of the OA-sensitive OTUs that benefitted the most from incubation in a closed bottle, as containment effects on the community structure were evident after 48 h. Many OTUs were adversely affected by sudden decreases of seawater pH, suggesting high sensitivity to OA at the base of the tropical marine biodiversity and difficult-to-predict outcomes for food-web functioning in the future ocean.

Microbial degradation influences the quality of oil resources. The environmental factors that shape the composition of oil microbial communities are largely unknown because most samples from oil fields are impacted by anthropogenic oil production, perturbing the native ecosystem with exogenous fluids and microorganisms. We investigated the relationship between formation water geochemistry and microbial community composition in undisturbed oil samples. We isolated 43 microliter-sized water droplets naturally enclosed in the heavy oil of the Pitch Lake, Trinidad and Tobago. The water chemistry and microbial community composition within the same water droplet were determined by ion chromatography and 16S rRNA gene amplicon sequencing, respectively. The results revealed a high variability in ion concentrations and community composition between water droplets. Microbial community composition was mostly affected by the chloride concentration, which ranged from freshwater to brackish-sea water. Remarkably, microbial communities did not respond gradually to increasing chloride concentration but showed a sudden change to less diverse and uneven communities when exceeding a chloride concentration of 57.3 mM. The results reveal a threshold-regulated response of microbial communities to salinity, offering new insights into the microbial ecology of oil reservoirs.

Anthropogenic carbon dioxide (CO2) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO2 in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO2 (pCO2=1823±161 μatm, pHT=7.46±0.05) versus in situ CO2 (pCO2=504±42 μatm, pHT=7.95±0.04) seawater on the community composition of marine planktonic eukaryotes immediately and after 48 hours of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Down-regulation of extracellular carbonic anhydrase occurred faster in the high CO2 treatment. Increased CO2 significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers. These effects were consistent between abundant (DNA-based) and active (cDNA-based) taxa after 48 hours, e.g., for the diatoms Trieres chinensis and Stephanopyxis turris. Effects were also very species-specific among different diatoms. Planktonic eukaryotes showed adaptation to the CO2 treatment over time, but many OTUs were adversely affected by decreasing pH. OA effects might fundamentally impact the base of marine biodiversity, suggesting profound outcomes for food web functioning in the future ocean. Competing Interest Statement The authors have declared no competing interest.

Multiple sclerosis (MS) is a putative T cell-mediated autoimmune disease. As with many autoimmune diseases, females are more susceptible than males. Sexual dimorphisms may be due to differences in sex hormones, sex chromosomes, or both. Regarding sex chromosome genes, a small percentage of X chromosome genes escape X inactivation and have higher expression in females (XX) compared with males (XY). Here, high-throughput gene expression analysis in CD4+ T cells showed that the top sexually dimorphic gene was Kdm6a, a histone demethylase on the X chromosome. There was higher expression of Kdm6a in females compared with males in humans and mice, and the four core genotypes (FCG) mouse model showed higher expression in XX compared with XY. Deletion of Kdm6a in CD4+ T cells ameliorated clinical disease and reduced neuropathology in the classic CD4+ T cell-mediated autoimmune disease experimental autoimmune encephalomyelitis (EAE). Global transcriptome analysis in CD4+ T cells from EAE mice with a specific deletion of Kdm6a showed upregulation of Th2 and Th1 activation pathways and downregulation of neuroinflammation signaling pathways. Together, these data demonstrate that the X escapee Kdm6a regulates multiple immune response genes, providing a mechanism for sex differences in autoimmune disease susceptibility.

Menopause is associated with cognitive deficits and brain atrophy, but the brain region and cell-specific mechanisms are not fully understood. Here, we identify a sex hormone by age interaction whereby loss of ovarian hormones in female mice at midlife, but not young age, induced hippocampal-dependent cognitive impairment, dorsal hippocampal atrophy, and astrocyte and microglia activation with synaptic loss. Selective deletion of estrogen receptor beta (ERβ) in astrocytes, but not neurons, in gonadally intact female mice induced the same brain effects. RNA sequencing and pathway analyses of gene expression in hippocampal astrocytes from midlife female astrocyte-ERβ conditional knock out (cKO) mice revealed Gluconeogenesis I and Glycolysis I as the most differentially expressed pathways. Enolase 1 gene expression was increased in hippocampi from both astrocyte-ERβ cKO female mice at midlife and from postmenopausal women. Gain of function studies showed that ERβ ligand treatment of midlife female mice reversed dorsal hippocampal neuropathology. Here the authors show in female mice at mid-life that deletion of estrogen receptor β in astrocytes induced cognitive impairment, hippocampal atrophy, glial activation and synaptic loss. ERβ ligand treatment restored cognition and decreased neuropathology in these animals.