Rhizobia-diatom symbiosis fixes missing nitrogen in the ocean.

Nitrogen (N2) fixation in oligotrophic surface waters is the main source of new nitrogen to the ocean1 and has a key role in fuelling the biological carbon pump2. Oceanic N2 fixation has been attributed almost exclusively to cyanobacteria, even though genes encoding nitrogenase, the enzyme that fixes N2 into ammonia, are widespread among marine bacteria and archaea3-5. Little is known about these non-cyanobacterial N2 fixers, and direct proof that they can fix nitrogen in the ocean has so far been lacking. Here we report the discovery of a non-cyanobacterial N2-fixing symbiont, 'Candidatus Tectiglobus diatomicola', which provides its diatom host with fixed nitrogen in return for photosynthetic carbon. The N2-fixing symbiont belongs to the order Rhizobiales and its association with a unicellular diatom expands the known hosts for this order beyond the well-known N2-fixing rhizobia-legume symbioses on land6. Our results show that the rhizobia-diatom symbioses can contribute as much fixed nitrogen as can cyanobacterial N2 fixers in the tropical North Atlantic, and that they might be responsible for N2 fixation in the vast regions of the ocean in which cyanobacteria are too rare to account for the measured rates.

Methylphosphonate-driven methane formation and its link to primary production in the oligotrophic North Atlantic.

Methylphosphonate is an organic phosphorus compound used by microorganisms when phosphate, a key nutrient limiting growth in most marine surface waters, becomes unavailable. Microbial methylphosphonate use can result in the formation of methane, a potent greenhouse gas, in oxic waters where methane production is traditionally unexpected. The extent and controlling factors of such aerobic methane formation remain underexplored. Here, we show high potential net rates of methylphosphonate-driven methane formation (median 0.4 nmol methane L-1 d-1) in the upper water column of the western tropical North Atlantic. The rates are repressed but still quantifiable in the presence of in-situ or added phosphate, suggesting that some methylphosphonate-driven methane formation persists in phosphate-replete waters. The genetic potential for methylphosphonate utilisation is present in and transcribed by key photo- and heterotrophic microbial taxa, such as Pelagibacterales, SAR116, and Trichodesmium. While the large cyanobacterial nitrogen-fixers dominate in the surface layer, phosphonate utilisation by Alphaproteobacteria appears to become more important in deeper depths. We estimate that at our study site, a substantial part (median 11%) of the measured surface carbon fixation can be sustained by phosphorus liberated from phosphonate utilisation, highlighting the ecological importance of phosphonates in the carbon cycle of the oligotrophic ocean.

Consenso Abem para o ensino de comunicação nas escolas médicas brasileiras / ABEM consensus for the brazilian medical schools' communication curriculum

Resumo: Introdução: A comunicação é uma competência essencial para o(a) médico(a) e outras categorias profissionais, e deve ser desenvolvida durante sua formação profissional. A elaboração de um projeto de comunicação, incluindo um consenso brasileiro, visou subsidiar as escolas médicas a preparar os estudantes de Medicina para se comunicarem efetivamente com os(as) cidadãos/cidadãs brasileiros(as), de características plurais intra e inter-regionais, pautando-se no profissionalismo e nos princípios do Sistema Único de Saúde (SUS). Objetivo: Este manuscrito apresenta o consenso para o ensino de comunicação nas escolas médicas brasileiras. Método: O consenso foi construído colaborativamente com 276 participantes, experts em comunicação, docentes, profissionais de saúde e discentes, de 126 escolas médicas e cinco instituições de saúde, ao longo de nove encontros presenciais em congressos e de encontros virtuais quinzenais ou mensais. Nos encontros, compartilharam-se as experiências dos participantes e o material bibliográfico, incluindo os consensos internacionais, e apresentou-se o consenso em construção, com discussão em grupos para elencar novos componentes para o consenso brasileiro, seguida por debate com todos para pactuá-los. A versão final foi aprovada em reunião virtual, com convite a todos(as) os(as) participantes em julho de 2021. Após submissão, diversas alterações foram requeridas, o que demandou novos encontros para revisão da versão final do consenso. Resultado: O consenso tem como pressupostos que a comunicação deve ser centrada nas relações, pautada nos princípios do SUS, na participação social e no profissionalismo, e embasada nas Diretrizes Curriculares Nacionais do curso de graduação em Medicina, em referenciais teóricos e nas evidências científicas. São descritos objetivos específicos para desenvolver a competência em comunicação nos estudantes, abrangendo: fundamentos teóricos; busca e avaliação crítica da literatura; elaboração e redação de documentos; comunicação intrapessoal e interpessoal no ambiente acadêmico-científico, na atenção à saúde em diversos contextos clínicos e na gestão em saúde. Recomenda-se a inserção curricular da comunicação do início ao final do curso, integrada a outros conteúdos e áreas de saber. Conclusão: Espera-se que esse consenso contribua para a revisão ou implementação da comunicação nos currículos das escolas médicas brasileiras.

Abstract: Introduction: Communication is an essential competence for the physician and other professional categories, and must be developed their professional training. The creation of a communication project including a Brazilian consensus aimed to subsidize medical schools in preparing medical students to communicate effectively with Brazilian citizens, with plural intra and inter-regional characteristics, based on the professionalism and the Brazilian Unified System (SUS) principles. Objective: The objective of this manuscript is to present the consensus for the teaching of communication in Brazilian medical schools. Method: The consensus was built collaboratively with 276 participants, experts in communication, faculty, health professionals and students from 126 medical schools and five health institutions in face-to-face conference meetings and biweekly or monthly virtual meetings. In the meetings, the participants' experiences and bibliographic material were shared, including international consensuses, and the consensus under construction was presented, with group discussion to list new components for the Brazilian consensus, followed by debate with everyone, to agree on them. The final version was approved in a virtual meeting with invitation to all participants in July 2021. After the submission, several changes were required, which demanded new meetings to review the consensus final version. Result: The consensus is based on assumptions that communication should be relationship-centered, embedded on professionalism, grounded on the SUS principles and social participation, and based on the National Guidelines for the undergraduate medical course, theoretical references and scientific evidence. Specific objectives to develop communication competence in the students are described, covering: theoretical foundations; literature search and its critical evaluation; documents drafting and editing; intrapersonal and interpersonal communication in the academicscientific environment, in health care and in health management; and, communication in diverse clinical contexts. The inclusion of communication in the curriculum is recommended from the beginning to the end of the course, integrated with other contents and areas of knowledge. Conclusion: It is expected that this consensus contributes the review or implementation of communication in Brazilian medical schools' curricula.

Purple sulfur bacteria fix N2 via molybdenum-nitrogenase in a low molybdenum Proterozoic ocean analogue.

Biological N2 fixation was key to the expansion of life on early Earth. The N2-fixing microorganisms and the nitrogenase type used in the Proterozoic are unknown, although it has been proposed that the canonical molybdenum-nitrogenase was not used due to low molybdenum availability. We investigate N2 fixation in Lake Cadagno, an analogue system to the sulfidic Proterozoic continental margins, using a combination of biogeochemical, molecular and single cell techniques. In Lake Cadagno, purple sulfur bacteria (PSB) are responsible for high N2 fixation rates, to our knowledge providing the first direct evidence for PSB in situ N2 fixation. Surprisingly, no alternative nitrogenases are detectable, and N2 fixation is exclusively catalyzed by molybdenum-nitrogenase. Our results show that molybdenum-nitrogenase is functional at low molybdenum conditions in situ and that in contrast to previous beliefs, PSB may have driven N2 fixation in the Proterozoic ocean.

Dark aerobic sulfide oxidation by anoxygenic phototrophs in anoxic waters.

Anoxygenic phototrophic sulfide oxidation by green and purple sulfur bacteria (PSB) plays a key role in sulfide removal from anoxic shallow sediments and stratified waters. Although some PSB can also oxidize sulfide with nitrate and oxygen, little is known about the prevalence of this chemolithotrophic lifestyle in the environment. In this study, we investigated the role of these phototrophs in light-independent sulfide removal in the chemocline of Lake Cadagno. Our temporally resolved, high-resolution chemical profiles indicated that dark sulfide oxidation was coupled to high oxygen consumption rates of ~9 µM O2 ·h-1 . Single-cell analyses of lake water incubated with 13 CO2 in the dark revealed that Chromatium okenii was to a large extent responsible for aerobic sulfide oxidation and it accounted for up to 40% of total dark carbon fixation. The genome of Chr. okenii reconstructed from the Lake Cadagno metagenome confirms its capacity for microaerophilic growth and provides further insights into its metabolic capabilities. Moreover, our genomic and single-cell data indicated that other PSB grow microaerobically in these apparently anoxic waters. Altogether, our observations suggest that aerobic respiration may not only play an underappreciated role in anoxic environments but also that organisms typically considered strict anaerobes may be involved.