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Abstract Marine algae produce complex polysaccharides, which can be degraded by marine heterotrophic bacteria utilizing carbohydrate-active enzymes. The red algal polysaccharide porphyran contains the methoxy sugar 6-O-methyl-d-galactose (G6Me). In the degradation of porphyran, oxidative demethylation of this monosaccharide towards d-galactose and formaldehyde occurs, which is catalyzed by a cytochrome P450 monooxygenase and its redox partners. In direct proximity to the genes encoding for the key enzymes of this oxidative demethylation, genes encoding for zinc-dependent alcohol dehydrogenases (ADHs) were identified, which seem to be conserved in porphyran utilizing marine Flavobacteriia. Considering the fact that dehydrogenases could play an auxiliary role in carbohydrate degradation, we aimed to elucidate the physiological role of these marine ADHs. Although our results reveal that the ADHs are not involved in formaldehyde detoxification, a knockout of the ADH gene causes a dramatic growth defect of Zobellia galactanivorans with G6Me as a substrate. This indicates that the ADH is required for G6Me utilization. Complete biochemical characterizations of the ADHs from Formosa agariphila KMM 3901T (FoADH) and Z. galactanivorans DsijT (ZoADH) were performed, and the substrate screening revealed that these enzymes preferentially convert aromatic aldehydes. Additionally, we elucidated the crystal structures of FoADH and ZoADH in complex with NAD+ and showed that the strict substrate specificity of these new auxiliary enzymes is based on a narrow active site. Key points • Knockout of the ADH-encoding gene revealed its role in 6-O-methyl-D-galactose utilization, suggesting a new auxiliary activity in marine carbohydrate degradation. • Complete enzyme characterization indicated no function in a subsequent reaction of the oxidative demethylation, such as formaldehyde detoxification. • These marine ADHs preferentially convert aromatic compounds, and their strict substrate specificity is based on a narrow active site.

Macroalgae represent huge amounts of biomass worldwide, largely recycled by marine heterotrophic bacteria. We investigated the strategies of bacteria within the flavobacterial genus Zobellia to initiate the degradation of whole algal tissues, which has received little attention compared to the degradation of isolated polysaccharides. Zobellia galactanivorans DsijT has the capacity to use fresh brown macroalgae as a sole carbon source and extensively degrades algal tissues via the secretion of extracellular enzymes, even in the absence of physical contact with the algae. Co-cultures experiments with the non-degrading strain Tenacibaculum aestuarii SMK-4T showed that Z. galactanivorans can act as a pioneer that initiates algal breakdown and shares public goods with other bacteria. A comparison of eight Zobellia strains, and strong transcriptomic shifts in Z. galactanivorans cells using fresh macroalgae vs. isolated polysaccharides, revealed potential overlooked traits of pioneer bacteria. Besides brown algal polysaccharide degradation, they notably include oxidative stress resistance proteins, type IX secretion system proteins and novel uncharacterized polysaccharide utilization loci. Overall, this work highlights the relevance of studying fresh macroalga degradation to fully understand the metabolic and ecological strategies of pioneer microbial degraders, key players in macroalgal biomass remineralization.

Coastal marine habitats constitute hotspots of primary productivity. In temperate regions, this is due both to massive phytoplankton blooms and dense colonization by macroalgae that mostly store carbon as glycans, contributing substantially to local and global carbon sequestration. Because they control carbon and energy fluxes, algae-degrading microorganisms are crucial for coastal ecosystem functions. Environmental surveys revealed consistent seasonal dynamics of alga-associated bacterial assemblages, yet resolving what factors regulate thein situabundance, growth rate and ecological functions of individual taxa remains a challenge. Here, we specifically investigated the seasonal dynamics of abundance and activity for a well-known alga-degrading marine flavobacterial genus in a tidally-mixed coastal habitat of the Western English Channel. We show that members of the genusZobelliaare a stable, low-abundance component of healthy macroalgal microbiota and can also colonize particles in the water column. This genus undergoes recurring seasonal variations with higher abundances in winter, significantly associated to biotic and abiotic variables.Zobelliacan become a dominant part of bacterial communities on decaying macroalgae, showing a strong activity and high estimatedin situgrowth rates. These results provide insights into the seasonal dynamics and environmental constraints driving natural populations of alga-degrading bacteria that influence coastal carbon cycling.Originality-significance statementGlycan-degrading bacteria play a crucial role in marine habitats to remineralize organic carbon sequestered in algal biomass. Yet, resolving what factors regulate thein situabundance, growth rate and ecological functions of individual taxa remains a challenge. Here, we investigate the seasonal dynamics of abundance and activity of an environmentally relevant glycan-degrading bacterial genus in two constrasted compartments of the same coastal habitat, i.e. the surface of diverse macroalgae and the water column. These results provide insights into the recurring temporal patterns and environmental constraints driving natural populations of alga-degrading bacteria that influence ocean carbon cycling.

Strain LLG6346-3.1T, isolated from the thallus of the brown algaEricaria zosteroidescollected in Mediterranean Sea near Bastia in Corsica, France, was characterized using a polyphasic method. Cells were Gram-stain-negative, strictly aerobic, non-flagellated, motile by gliding, rod-shaped and grew optimally at 30-33 °C, at pH 8-8.5 and with 4-5 % NaCl. Strain LLG6346-3.1Tused the seaweed polysaccharide alginic acid as sole carbon source which was vigorously liquefied. Phylogenetic analyses showed that the bacterium is affiliated to the genusZobellia(familyFlavobacteriaceae, classFlavobacteriia). Strain LLG6346-3.1Texhibited 16S rRNA gene sequence similarity values of 98.5 and 98.3 % to the type strains ofZobellia russelliiandZobellia roscoffensisrespectively, and of 97.4-98.2 % to other species of the genusZobellia. The DNA G+C content of strain LLG6346-3.1Twas determined to be 38.28 mol%. Digital DNA-DNA hybridization predictions by the ANI and GGDC methods between strain LLG6346-3.1Tand other members of the genusZobelliashowed values of 76-88 %, and below 37 %, respectively. The phenotypic, phylogenetic and genomic analyses show that strain LLG6346-3.1Tis distinct from species of the genusZobelliawith validly published names and that it represents a novel species of the genusZobellia, for which the nameZobellia alginoliquefacienssp. nov. is proposed. The type strain is LLG6346-3.1T(RCC 7657T= LLG 32918T).

International audience; Learning to read and comprehend a written text is crucial for a child’s happiness and success.. However, a large proportion of children in school encounter difficulties in acquiring this skill. In this context, the aim of our study was to determine whether text simplification, a process of reducing the complexity of a text while retaining its meaning, can improve reading fluency and comprehension in children who are learning to read. In addition, we wanted to find out if poor readers or children with poor oral language skills benefit more from simplification than normal readers or children with good oral language skills? All children were presented with informational and literary texts either in its original or simplified version through an iBook application. The overall results seem to suggest that poor readers and children with weaker cognitive abilities benefit to a greater extent from text simplification.

The present study offers a meta-analysis of effectiveness studies on dialogue-based CALL, i.e., systems allowing a learner to practice a second language (L2) by interact- ing with a conversational agent (“bot”). Through a systematic inclusion and exclusion process, screening 419 publications, we identified 17 relevant meta-analyzable studies. We made use of Morris and DeShon’s (2002) formulas to compute comparable effect sizes across designs, including 𝑘 = 100 individual effect sizes, which were analyzed through a multilevel random-effects model. Results confirm that dialogue-based CALL practice has a significant medium effect size on L2 proficiency development (𝑑 = 0.59). We performed extensive moderator analyses to explore the relative effectiveness on several learning outcomes of different types and features of dialogue-based CALL (type of interaction, modality, agent embodiment, etc.). In particular, our study confirms the effectiveness of form-focused and goal-oriented systems, system-guided interactions, corrective feedback provision, and gamification features. Significant effects for lower proficiency learners, and on vocabulary, morphosyntax, holistic proficiency, and accuracy are established. Finally, we discuss evolutions to be expected in dialogue-based CALL and the language learning opportunities it offers. ispartof: Language Learning & Technology vol:26 issue:1 pages:1-24 status: published

Annotations of word difficulty by readers provide invaluable insights into lexical complexity. Yet, there is currently a paucity of tools allowing researchers to gather such annotations in an adaptable and simple manner. This article presents PADDLe, an online platform aiming to fill that gap and designed to encourage best practices when collecting difficulty judgements. Studies crafted using the tool ask users to provide a selection of demographic information, then to annotate a certain number of texts and answer multiple-choice comprehension questions after each text. Researchers are encouraged to use a multi-level annotation scheme, to avoid the drawbacks of binary complexity annotations. Once a study is launched, its results are summarised in a visual representation accessible both to researchers and teachers, and can be downloaded in .csv format. Some findings of a pilot study designed with the tool are also provided in the article, to give an idea of the types of research questions it allows to answer.

Reducing the complexity of texts by applying an Automatic Text Simplification (ATS) system has been sparking interest in the area of Natural Language Processing (NLP) for several years and a number of methods and evaluation campaigns have emerged targeting lexical and syntactic transformations. In recent years, several studies exploit deep learning techniques based on very large comparable corpora. Yet the lack of large amounts of corpora (original-simplified) for French has been hindering the development of an ATS tool for this language. In this paper, we present our system, which is based on a combination of methods relying on word embeddings for lexical simplification and rule-based strategies for syntax and discourse adaptations. We present an evaluation of the lexical, syntactic and discourse-level simplifications according to automatic and human evaluations. We discuss the performances of our system at the lexical, syntactic, and discourse levels.

Formaldehyde is a toxic metabolite that is formed in large quantities during bacterial utilization of the methoxy sugar 6-O-methyl-d-galactose, an abundant monosaccharide in the red algal polysaccharide porphyran. Marine bacteria capable of metabolizing porphyran must therefore possess suitable detoxification systems for formaldehyde. We demonstrate here that detoxification of formaldehyde in the marine Flavobacterium Zobellia galactanivorans proceeds via the ribulose monophosphate pathway. Simultaneously, we show that the genes encoding the key enzymes of this pathway are important for maintaining high formaldehyde resistance. Additionally, these genes are upregulated in the presence of porphyran, allowing us to connect porphyran degradation to the detoxification of formed formaldehyde.

La pandemie de sars-cov-2 a profondement modifie le rapport au travail en reanimation. Si l'ensemble des metiers soignants a su, rapidement et efficacement se reorganiser, les retentissements psychiques sont nombreux et durables : effets de la contagiosite sur la distance soignant-malade, consequences sur la relation soignant-soigne alterant la dimension ethique du soin, perte de sens devant les manques de moyens humains et materiels. Les cellules d'ecoute, dont celles d'AML-soins intensifs, ont recueilli les angoisses, les coleres et les espoirs des professionnels de reaniamtion.

Although many different mechanisms for subduction initiation have been proposed, only few of them are viable in terms of consistency with observations and reproducibility in numerical experiments. In particular, it has recently been demonstrated that intra‐oceanic subduction triggered by an upwelling mantle plume could greatly contribute to the onset and operation of plate tectonics in the early and, to a lesser degree, modern Earth. On the contrary, the initiation of intra‐continental subduction still remains underappreciated. Here we provide an overview of 1) observational evidence for upwelling of hot mantle material flanked by downgoing proto‐slabs of sinking continental mantle lithosphere, and 2) previously published and new numerical models of plume‐induced subduction initiation. Numerical modeling shows that under the condition of a sufficiently thick (>100 km) continental plate, incipient downthrusting at the level of the lowermost lithospheric mantle can be triggered by plume anomalies of moderate temperatures and without significant strain‐ and/or melt‐related weakening of overlying rocks. This finding is in contrast with the requirements for plume‐induced subduction initiation within oceanic or thinner continental lithosphere. As a result, plume‐lithosphere interactions within continental interiors of Paleozoic‐Proterozoic‐(Archean) platforms are the least demanding (and thus potentially very common) mechanism for initiation of subduction‐like foundering in the Phanerozoic Earth. Our findings are supported by a growing body of new geophysical data collected in various intra‐continental areas. A better understanding of the role of intra‐continental mantle downthrusting and foundering in global plate tectonics and, particularly, in the initiation of “classic” ocean‐continent subduction will benefit from more detailed follow‐up investigations. ISSN:1525-2027

International audience; Kelps are dominant primary producers in temperate coastal ecosystems. Large amounts of kelp biomass can be exported to the seafloor during the algal growth cycle or following storms, creating new ecological niches for the associated microbiota. Here, we investigated the bacterial community associated with the kelp Laminaria hyperborea during its accumulation and degradation on the seafloor. Kelp tissue, seawater and sediment were sampled during a 6-month in situ experiment simulating kelp detritus accumulation. Evaluation of the epiphytic bacterial community abundance, structure, taxonomic composition and predicted functional profiles evidenced a biphasic succession. Initially, dominant genera (Hellea, Litorimonas, Granulosicoccus) showed a rapid and drastic decrease in sequence abundance, probably outcompeted by algal polysaccharide-degraders such as Bacteroidia members which responded within 4 weeks. Acidimicrobiia, especially members of the Sva0996 marine group, colonized the degrading kelp biomass after 11 weeks. These secondary colonizers could act as opportunistic scavenger bacteria assimilating substrates exposed by early degraders. In parallel, kelp accumulation modified bacterial communities in the underlying sediment, notably favouring anaerobic taxa potentially involved in the sulfur and nitrogen cycles. Overall, this study provides insights into the bacterial degradation of algal biomass in situ, an important link in coastal trophic chains.