Paralytic shellfish toxins producing dinoflagellates cause dysbacteriosis in scallop gut microbial biofilms.

Filter-feeding bivalves could accumulate paralytic shellfish toxins (PSTs) produced by harmful dinoflagellates through diet. Despite that bivalves are resistant to these neurotoxins due to possessing PST-resistant sodium channel, exposure to PSTs-producing dinoflagellates impair bivalve survival. We hypothesized that ingesting PSTs-producing dinoflagellates may influence the gut microbiota, and then the health of bivalves. To test this idea, we compared the gut microbiota of the scallop Patinopecten yessoensis, after feeding with PST-producing or non-toxic dinoflagellates. Exposure to PSTs-producing dinoflagellates resulted in a decline of gut microbial diversity and a disturbance of community structure, accompanied by a significant increase in the abundance and richness of pathogenic bacteria, represented by Vibrio. Moreover, network analysis demonstrated extensive positive correlations between pathogenic bacteria abundances and PSTs concentrations in the digestive glands of the scallops. Furthermore, isolation of a dominant Vibrio strain and its genomic analysis revealed a variety of virulence factors, including the tolC outer membrane exporter, which were expressed in the gut microbiota. Finally, the infection experiment demonstrated scallop mortality caused by the isolated Vibrio strain; further, the pathogenicity of this Vibrio strain was attenuated by a mutation in the tolC gene. Together, these findings demonstrated that the PSTs may affect gut microbiota via direct and taxa-specific interactions with opportunistic pathogens, which proliferate after transition from seawater to the gut environment. The present study has revealed novel mechanisms towards deciphering the puzzles in environmental disturbances-caused death of an important aquaculture species.

Biofilm formation stabilizes metabolism in a Roseobacteraceae bacterium under temperature increase.

Ocean warming profoundly impacts microbes in marine environments; yet, how lifestyle (e.g., free living versus biofilm associated) affects the bacterial response to rising temperature is not clear. Here, we compared transcriptional, enzymatic, and physiological responses of free-living and biofilm-associated Leisingera aquaemixtae M597, a member of the Roseobacteraceae family isolated from marine biofilms, to the increase in temperature from 25℃ to 31℃. Complete genome sequencing and metagenomics revealed the prevalence of M597 in global ocean biofilms. Transcriptomics suggested a significant effect on the expression of genes related to carbohydrate metabolism, nitrogen and sulfur metabolism, and phosphorus utilization of free-living M597 cells due to temperature increase, but such drastic alterations were not observed in its biofilms. In the free-living state, the transcription of the key enzyme participating in the Embden-Meyerhof-Parnas pathway was significantly increased due to the increase in temperature, accompanied by a substantial decrease in the Entner-Doudoroff pathway, but transcripts of these glycolytic enzymes in biofilm-forming strains were independent of the temperature variation. The correlation between the growth condition and the shift in glycolytic pathways under temperature change was confirmed by enzymatic activity assays. Furthermore, the rising temperature affected the growth rate and the production of intracellular reactive oxygen species when M597 cells were free living rather than in biofilms. Thus, biofilm formation stabilizes metabolism in M597 when grown under high temperature and this homeostasis is probably related to the glycolytic pathways.IMPORTANCEBiofilm formation is one of the most successful strategies employed by microbes against environmental fluctuations. In this study, using a marine Roseobacteraceae bacterium, we studied how biofilm formation affects the response of marine bacteria to the increase in temperature. This study enhances our understanding of the function of bacterial biofilms and the microbe-environment interactions in the framework of global climate change.

Early stage of biofilm assembly on microplastics is structured by substrate size and bacterial motility.

The taxonomic structure of biofilms on 0.3-mm microplastics differed significantly from that on 3-mm microplastics or glass particles. Compared with the 3-mm microplastics, biofilms on 0.3-mm microplastics were enriched for genes involved in flagellar-based motility and chemotaxis, pointing to a more 'mobile' community. The association between motility and bacterial colonization of 0.3-mm microplastics was observed through laboratory experiments using isolated strains.

Unravelling nutrient fate and CO2 concentrations in the reservoirs of the Seine Basin using a modelling approach.

Reservoirs are active reactors for the biogeochemical cycling of carbon (C) and nutrients (nitrogen: N, phosphorus: P, and silica: Si), however, our in-depth understanding of C and nutrient cycling in reservoirs is still limited by the fact that it involves a variety of closely linked and coupled biogeochemical and hydrological processes. In this study, the updated process-based Barman model was applied to three reservoirs of the Seine Basin during 2019-2020, considering the variations of carbon dioxide (CO2) concentrations and key water quality variables. The model simulations captured well the observed seasonal variations of water quality variables, although discrepancies remained for some variables. According to the model, we found that: (1) the three reservoirs are autotrophic ecosystems and showed high removal efficiency of dissolved inorganic carbon and nutrients during 2019-2020; (2) phytoplankton assimilation, benthic denitrification, precipitation and dissolution of calcium carbonate, and gas exchange at the water-air interface are the dominant processes for water quality variations in reservoirs; (3) based on scenarios results, trophic state and mean water depth of reservoir would impact the biogeochemical processes and the retention efficiency of nitrate and dissolved silicate. Finally, we expect that the successful application of Barman model in the reservoirs of the Seine Basin could provide a useful tool for simulating reservoir water quality changes and thus evaluating the impacts of reservoirs on downstream water quality.

Strategies for Zinc Uptake in Pseudomonas aeruginosa at the Host-Pathogen Interface.

As a structural, catalytic, and signaling component, zinc is necessary for the growth and development of plants, animals, and microorganisms. Zinc is also essential for the growth of pathogenic microorganisms and is involved in their metabolism as well as the regulation of various virulence factors. Additionally, zinc is necessary for infection and colonization of pathogenic microorganisms in the host. Upon infection in healthy organisms, the host sequesters zinc both intracellularly and extracellularly to enhance the immune response and prevent the proliferation and infection of the pathogen. Intracellularly, the host manipulates zinc levels through Zrt/Irt-like protein (ZIP)/ZnT family proteins and various zinc storage proteins. Extracellularly, members of the S100 protein family, such as calgranulin C, sequester zinc to inhibit microbial growth. In the face of these nutritional limitations, bacteria rely on an efficient zinc transport system to maintain zinc supplementation for proliferation and disruption of the host defense system to establish infection. Here, we summarize the strategies for zinc uptake in conditional pathogenic Pseudomonas aeruginosa, including known zinc uptake systems (ZnuABC, HmtA, and ZrmABCD) and the zinc uptake regulator (Zur). In addition, other potential zinc uptake pathways were analyzed. This review systematically summarizes the process of zinc uptake by P. aeruginosa to provide guidance for the development of new drug targets.

Oxygen data assimilation for estimating micro-organism communities' parameters in river systems.

The coupling of high frequency data of water quality with physically based models of river systems is of great interest for the management of urban socio-ecosystems. One approach to exploit high frequency data is data assimilation which has received an increasing attention in the field of hydrology, but not for water quality modeling so far. We present here a first implementation of a particle filtering algorithm into a community-centered hydro-biogeochemical model to assimilate high frequency dissolved oxygen data and to estimate metabolism parameters in the Seine River system. The procedure is designed based on the results of a former sensitivity analysis of the model (Wang et al., 2018) that allows for the identification of the twelve most sensible parameters all over the year. Those parameters are both physical and related to micro-organisms (reaeration coefficient, photosynthetic parameters, growth rates, respiration rates and optimal temperature). The performances of the approach are assessed on a synthetic case study that mimics 66 km of the Seine River. Virtual dissolved oxygen data are generated using time varying parameters. This paper aims at retrieving the predefined parameters by assimilating those data. The simulated dissolved oxygen concentrations match the reference concentrations. The identification of the parameters depends on the hydrological and trophic contexts and more surprisingly on the thermal state of the river. The physical, bacterial and phytoplanktonic parameters can be retrieved properly, leading to the differentiation of two successive algal blooms by comparing the estimated posterior distribution of the optimal temperature for phytoplankton growth. Finally, photosynthetic parameters' distributions following circadian cycles during algal blooms are discussed.

Time-dependent global sensitivity analysis of the C-RIVE biogeochemical model in contrasted hydrological and trophic contexts.

Dissolved oxygen within water column is a key variable to characterize the water quality. Water quality modeling has been extensively developed for decades. However, complex biogeochemical cycles are described using a high number of parameters. Hence, parameters' uncertainty constitutes a major problem in the application of these models. Sensitivity analysis allows the identification of the most influential parameters in a model and a better understanding of the governing processes. This paper presents a time-dependent sensitivity analysis for dissolved oxygen using Morris and Sobol methods combined with a functional principal components analysis for dimension reduction. The aim of this study is to identify the most important parameters of C-RIVE model in different trophic contexts and to understand the biogeochemical functioning of river systems. The results indicate that the maintenance respiration of phytoplankton and the photosynthetic parameters (i.e. photosynthetic capacity, the maximal photosynthesis rate and light extinction coefficients) are the most influential parameters during algal blooms. When the river system becomes heterotrophic, the bacterial activities (moderate and high temperature) and the reaeration coefficients (low temperature) affect the most the dissolved oxygen concentration in the water column. An anthropogenic effect (ship navigation) on variation of dissolved oxygen concentration has been identified and the role of this anthropogenic effect evolves with hydrological and trophic conditions.

Arsenic Incorporation in Pyrite at Ambient Temperature at Both Tetrahedral S-I and Octahedral FeII Sites: Evidence from EXAFS-DFT Analysis.

Pyrite is a ubiquitous mineral in reducing environments and is well-known to incorporate trace elements such as Co, Ni, Se, Au, and commonly As. Indeed, As-bearing pyrite is observed in a wide variety of sedimentary environments, making it a major sink for this toxic metalloid. Based on the observation of natural hydrothermal pyrites, As-I is usually assigned to the occupation of tetrahedral S-I sites, with the same oxidation state as in arsenopyrite (FeAsS), although rare occurrences of AsIII and AsII have been reported. However, the modes of As incorporation into pyrite during its crystallization under low-temperature diagenetic conditions have not yet been elucidated because arsenic acts as an inhibitor for pyrite nucleation at ambient temperature. Here, we provide evidence from X-ray absorption spectroscopy for AsII,III incorporation into pyrite at octahedral FeII sites and for As-I at tetrahedral S-I sites during crystallization at ambient temperature. Extended X-ray absorption fine structure (EXAFS) spectra of these As-bearing pyrites are explained by local structure models obtained using density functional theory (DFT), assuming incorporation of As at the Fe and S sites, as well as local clustering of arsenic. Such observations of As-I incorporation at ambient temperature can aid in the understanding of the early formation of authigenic arsenian pyrite in subsurface sediments. Moreover, evidence for substitution of AsII,III for Fe in our synthetic samples raises questions about both the possible occurrence and the geochemical reactivity of such As-bearing pyrites in low-temperature subsurface environments.