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Marine sediments impacted by urban and industrial pollutants are typically exposed to reducing conditions and represent major reservoirs of toxic mercury species. Mercury methylation mediated by anaerobic microorganisms is favored under such conditions, yet little is known about potential microbial mechanisms for mercury detoxification. We used culture-independent (metagenomics, metabarcoding) and culture-dependent approaches in anoxic marine sediments to identify microbial indicators of mercury pollution and analyze the distribution of genes involved in mercury reduction (merA) and demethylation (merB). While none of the isolates featured merB genes, 52 isolates, predominantly affiliated with Gammaproteobacteria, were merA positive. In contrast, merA genes detected in metagenomes were assigned to different phyla, including Desulfobacterota, Actinomycetota, Gemmatimonadota, Nitrospirota, and Pseudomonadota. This indicates a widespread capacity for mercury reduction in anoxic sediment microbiomes. Notably, merA genes were predominately identified in Desulfobacterota, a phylum previously associated only with mercury methylation. Marker genes involved in the latter process (hgcAB) were also mainly assigned to Desulfobacterota, implying a potential central and multifaceted role of this phylum in the mercury cycle. Network analysis revealed that Desulfobacterota were associated with anaerobic fermenters, methanogens and sulfur-oxidizers, indicating potential interactions between key players of the carbon, sulfur and mercury cycling in anoxic marine sediments

Drought is the most detrimental abiotic stress in agriculture, limiting crop growth and yield and, currently, its risk is increasing due to climate change. Thereby, ensuring food security will be one of the greatest challenges of the agriculture in the nearest future, accordingly it is essential to look for sustainable strategies to cope the negative impact of drought on crops. Inoculation of pulses with biostimulants such as rhizobium strains with high nitrogen fixation efficiency and drought-tolerance, has emerged as a promising and sustainable production strategy. However, some commercial inoculums are not effective under field conditions due to its lower effectiveness against indigenous rhizobium strains in the establishment of the symbiosis. Thus, in the present study, we evaluated the ability to improve drought tolerance in common bean plants of different indigenous rhizobia strains isolated from nearby crop fields in the Basque Country either affected by drought or salinity. The plants in this trial were grown in a climatic chamber under controlled conditions and exposed to values of 30% relative soil water content at the time of harvest, which is considered a severe drought. From the nine bacteria strains evaluated, three were found to be highly efficient under drought (namely 353, A12 and A13). These strains sustained high infectiveness (nodulation capacity) and effectiveness (shoot biomass production) under drought, even surpassing the plants inoculated with the CIAT899 reference strain, as well as the chemically N-fertilized plants. The tolerance mechanisms developed by plants inoculated with 353, A12 and A13 strains were a better adjustment of the cell wall elasticity that prevents mechanical damages in the plasma membrane, a higher WUE and an avoidance of the phenological delay caused by drought, developing a greater number of flowers. These results provide the basis for the development of efficient common bean inoculants able to increase the yield of t

Isolation of microorganisms is a useful approach to gathering knowledge about their genomic properties, physiology, and ecology, in addition to allowing the characterization of novel taxa. We performed an extensive isolation effort on samples from seawater manipulation experiments that were carried out during the four astronomical seasons in a coastal site of the northwest Mediterranean to evaluate the impact of grazing, viral mortality, resource competition reduction, and light presence/absence on bacterioplankton growth. Isolates were retrieved using two growth media, and their full 16S rRNA gene was sequenced to assess their identity and calculate their culturability across seasons and experimental conditions. A total of 1,643 isolates were obtained, mainly affiliated to the classes Gammaproteobacteria (44%), Alphaproteobacteria (26%), and Bacteroidia (17%). Isolates pertaining to class Gammaproteobacteria were the most abundant in all experiments, while Bacteroidia were preferentially enriched in the treatments with reduced grazing. Sixty-one isolates had a similarity below 97% to cultured taxa and are thus putatively novel. Comparison of isolate sequences with 16S rRNA gene amplicon sequences from the same samples showed that the percentage of reads corresponding to isolates was 21.4% within the whole data set, with dramatic increases in the summer virus-reduced (71%) and diluted (47%) treatments. In fact, we were able to isolate the top 10 abundant taxa in several experiments and from the whole data set. We also show that top-down and bottom-up controls differentially affect taxa in terms of culturability. Our results indicate that culturing marine bacteria using agar plates can be successful in certain ecological situations

Anthropogenic perturbations have tripled the mercury (Hg) content of ocean waters compared to pre-anthropogenic conditions but the impact of this Hg increase is not uniform across the ocean. . In particular, the controls on contaminant levels of Hg and one of its dangerous species, methyl-mercury (MeHg), in the deep ocean at global scale remain largely unknown. We explored 52 globally-distributed deep ocean metagenomes and 26 metatranscriptomes of the Malapasina 2010 circumnavigation from two different plankton size fractions (0.2-0.8 ¿m and 0.8-20 ¿m), commonly referred to the life-style of free-living and particle-attached microorganisms, respectively. Our results unveil the biogeography and expression patterns of genes related to HgII reduction and MeHg degradation, merA and merB, respectively, in the bathypelagic (~ 4000 m) ocean realm. We report the main taxonomic players involved in the Hg volatilization and MeHg degradation in the poorly studied bathypelagic ocean including members of the Corynerbacteriales, Rhodobacterales, Alteromonadales, Oceanospirillales, Moraxellales and Flavobacteriales orders. Moreover, the composition of the organic matter and water masses age and were good predictors of the abundance and expression levels of merA and merB genes, and thus provided new insights into the global Hg biogeochemical cycle

It is well known that only a small fraction of the marine microbial diversity, which mainly belong to the so-called rare biosphere, can be retrieved by isolation. However, this paradigm has not been fully tested at a broad scale, especially in the deep ocean and in the ocean particle microbiome. Here, we compared 16S rRNA gene sequences from a large collection (>2000) of cultured heterotrophic marine bacteria with global 16S rRNA metabarcoding (16S Tags) datasets covering surface, mesopelagic and bathypelagic ocean samples that included 16 of the 22 samples used for isolation. These global datasets represent 60.322 unique 16S amplicon sequence variants (ASVs). Our results reveal a significantly higher proportion of isolates identical to ASVs in deeper ocean layers, which included the isolation of 3 of the top 10 most abundant 16S ASVs in the global bathypelagic ocean, related to the genera Sulfitobacter, Halomonas and Erythrobacter. These isolates contributed differently to the prokaryotic communities across different plankton size fractions, recruiting between 38% in the free-living fraction (0.2 -0.8 ¿m) and up to 45% in the largest particles (20-200 ¿m) in the bathypelagic ocean. Our findings support the hypothesis that sinking particles in the bathypelagic act as resource-rich habitats, suitable for the growth of heterotrophic bacteria with a copiotroph lifestyle that can be cultured, and that these cultivable bacteria can also thrive as free-living bacteria

Traditional culture techniques usually retrieve a small fraction of the marine microbial diversity, which mainly belong to the so-called rare biosphere. However, this paradigm has not been fully tested at a broad scale, especially in the deep ocean. Here, we examined the fraction of heterotrophic bacterial communities in photic and deep ocean layers that could be recovered by culture-dependent techniques at a large scale. We compared 16S rRNA gene sequences from a collection of 2003 cultured heterotrophic marine bacteria with global 16S rRNA metabarcoding datasets (16S TAGs) covering surface, mesopelagic and bathypelagic ocean samples that included 16 of the 23 samples used for isolation. These global datasets represent 60 322 unique 16S amplicon sequence variants (ASVs). Our results reveal a significantly higher proportion of isolates identical to ASVs in deeper ocean layers reaching up to 28% of the 16S TAGs of the bathypelagic microbial communities, which included the isolation of 3 of the top 10 most abundant 16S ASVs in the global bathypelagic ocean, related to the genera Sulfitobacter, Halomonas and Erythrobacter. These isolates contributed differently to the prokaryotic communities across different plankton size fractions, recruiting between 38% in the free-living fraction (0.2–0.8 µm) and up to 45% in the largest particles (20–200 µm) in the bathypelagic ocean. Our findings support the hypothesis that sinking particles in the bathypelagic act as resource-rich habitats, suitable for the growth of heterotrophic bacteria with a copiotroph lifestyle that can be cultured, and that these cultivable bacteria can also thrive as free-living bacteria

[EN] The details of this research, led by the Institut de Ciències del Mar (ICM-CSIC) and the Universitat Autònoma de Barcelona (UAB), are reported in an article published recently in the prestigious journal ISME Communications, [ES] Los detalles de la investigación, liderada por el Institut de Ciències del Mar (ICM-CSIC) y la Universitat Autònoma de Barcelona (UAB), se recogen en un artículo publicado recientemente en la prestigiosa revista ISME Communications, [CAT] Els detalls de la investigació, liderada per l'Institut de Ciències del Mar (ICM-CSIC) i la Universitat Autònoma de Barcelona (UAB), es recullen en un article publicat recentment a la prestigiosa revista ISME Communications