Project description:The Baltic Sea is one of the largest brackish water bodies in the world. Redoxclines that form between oxic and anoxic layers in the deepest sub-basins are a semi-permanent character of the pelagic Baltic Sea. The microbially mediated nitrogen removal processes in these redoxclines have been recognized as important ecosystem service that removes large proportion of the nitrogen load originating from the drainage basin. However, nitrification, which links mineralization of organic nitrogen and nitrogen removal processes, has remained poorly understood. To gain better understanding of the nitrogen cycling in the Baltic Sea, we analyzed the assemblage of ammonia oxidizing bacteria and archaea in the central Baltic Sea using functional gene microarrays and measured the biogeochemical properties along with potential nitrification rates. Overall, the ammonia oxidizer communities in the Baltic Sea redoxcline were very evenly distributed. However, the communities were clearly different between the eastern and western Gotland Basin and the correlations between different components of the ammonia oxidizer assemblages and environmental variables suggest ecological basis for the community composition. The more even community ammonia oxidizer composition in the eastern Gotland Basin may be related to the constantly oscillating redoxcline that does not allow domination of single archetype. The oscillating redoxcline also creates long depth range of optimal nitrification conditions. The rate measurements suggest that nitrification in the central Baltic Sea is able to produce all nitrate required by denitrification occurring below the nitrification zone.
Project description:The Baltic Sea is one of the largest brackish water bodies in the world. Redoxclines that form between oxic and anoxic layers in the deepest sub-basins are a semi-permanent character of the pelagic Baltic Sea. The microbially mediated nitrogen removal processes in these redoxclines have been recognized as important ecosystem service that removes large proportion of the nitrogen load originating from the drainage basin. However, nitrification, which links mineralization of organic nitrogen and nitrogen removal processes, has remained poorly understood. To gain better understanding of the nitrogen cycling in the Baltic Sea, we analyzed the assemblage of ammonia oxidizing bacteria and archaea in the central Baltic Sea using functional gene microarrays and measured the biogeochemical properties along with potential nitrification rates. Overall, the ammonia oxidizer communities in the Baltic Sea redoxcline were very evenly distributed. However, the communities were clearly different between the eastern and western Gotland Basin and the correlations between different components of the ammonia oxidizer assemblages and environmental variables suggest ecological basis for the community composition. The more even community ammonia oxidizer composition in the eastern Gotland Basin may be related to the constantly oscillating redoxcline that does not allow domination of single archetype. The oscillating redoxcline also creates long depth range of optimal nitrification conditions. The rate measurements suggest that nitrification in the central Baltic Sea is able to produce all nitrate required by denitrification occurring below the nitrification zone. Two color array (Cy3 and Cy5): the universal standard 20-mer oligo is printed to the slide with a 70-mer oligo (an archetype). Environmental DNA sequences (fluoresced with Cy3) within 15% of the 70-mer conjugated to a 20-mer oligo (fluoresced with Cy5) complementary to the universal standard will bind to the oligo probes on the array. Signal is the ratio of Cy3 to Cy5. Three replicate probes were printed for each archetype. Two replicate arrays were run on duplicate targets.
Project description:During the legume-rhizobium symbiosis, free-living soil bacteria known as rhizobia trigger the formation of root nodules. The rhizobia infect these organs and adopt an intracellular lifestyle within the symbiotic nodule cells where they become nitrogen-fixing bacteroids. Several legume lineages enforce their symbionts into an extreme cellular differentiation, comprising cell enlargement and genome endoreduplication. The antimicrobial peptide transporter BclA is a major determinant of this differentiation process in Bradyrhizobium sp. ORS285, a symbiont of Aeschynomene spp.. In the absence of BclA, Bradyrhizobium sp. ORS285 proceeds until the intracellular infection of nodule cells but the bacteria cannot differentiate into enlarged polyploid bacteroids and fix nitrogen. The nodule bacteria of the bclA mutant constitute thus an intermediate stage between the free-living soil bacteria and the intracellular nitrogen-fixing bacteroids. Metabolomics on whole nodules of Aeschynomene afraspera and Aeschynomene indica infected with the ORS285 wild type or the bclA mutant revealed 47 metabolites that differentially accumulated concomitantly with bacteroid differentiation. Bacterial transcriptome analysis of these nodules discriminated nodule-induced genes that are specific to differentiated and nitrogen-fixing bacteroids and others that are activated in the host microenvironment irrespective of bacterial differentiation and nitrogen fixation. These analyses demonstrated that the intracellular settling of the rhizobia in the symbiotic nodule cells is accompanied with a first transcriptome switch involving several hundreds of upregulated and downregulated genes and a second switch accompanying the bacteroid differentiation, involving less genes but that are expressed to extremely elevated levels. The transcriptomes further highlighted the dynamics of oxygen and redox regulation of gene expression during nodule formation and we discovered that bclA represses the expression of non-ribosomal peptide synthetase gene clusters suggesting a non-symbiotic function of BclA. Together, our data uncover the metabolic and gene expression changes that accompany the transition from intracellular bacteria into differentiated nitrogen-fixing bacteroids.
Project description:Transcriptomic analyses using high-throughput methods have revealed abundant antisense transcription in bacteria. Most frequently, antisense transcription is due to the overlap of mRNAs with long 5’ regions or 3’ ends that extend beyond the coding sequence. In addition, antisense RNAs that do not contain any coding sequence are also observed. Nostoc sp. PCC 7120 is a filamentous cyanobacterium that, under nitrogen limitation, behaves as a multicellular organism with division of labor among two different cell types that depend on each other, the vegetative CO2-fixing cells and the nitrogen-fixing heterocysts. Differentiation of heterocysts depends on the global nitrogen regulator NtcA and requires the specific regulator HetR. To identify antisense RNAs potentially involved in heterocyst differentiation we performed an RNA-Seq analysis of cells subjected to nitrogen limitation (either at 9 or 24 hours after nitrogen removal) and analyzed the results in combination with a genome-wide set of nitrogen-regulated transcriptional start sites and a prediction of transcriptional terminators. Our analysis resulted in the definition of a transcriptional map including more than 4,000 transcripts, 65% of them in antisense orientation to other transcripts. In addition to overlapping mRNAs we identified nitrogen-regulated non-coding antisense RNAs transcribed from NtcA-dependent or HetR-dependent promoters.
Project description:For the filamentous cyanobacterium Anabaena variabilis to grow without combined nitrogen, certain cells differentiate into heterocysts that fix N2, while vegetative cells perform photosynthesis. Much remains unknown on how heterocysts differ from vegetative cells in terms of carbon and energy metabolisms. Microarrays were used to investigate gene transcription patterns in vegetative cells, heterocysts, and filaments of N2-fixing phototrophic, mixotrophic, and heterotrophic cultures.
Project description:In this study, transcriptomics was used to investigate Atlantic salmon (Salmo salar) sampled from three different field locations within Baltic Sea (Baltic Main Basin (CBS), Gulf of Finland (GoF) and Bothnian Sea (BS)) during marine migration. RNA labeling, hybridizations, and scanning were performed by the Finnish Microarray and Sequencing Centre in Turku Centre for Biotechnology.
Project description:Casuarina glauca belongs to a family of angiosperms called actinorhizal plants because they can develop nitrogen-fixing nodules in association with the soil bacteria Frankia. The aim of this transcriptomic study was to get a global view of the plant symbiotic genetic program and to identify new key plant genes that control nodulation during symbiosis in C. glauca. Symbiosis between C. glauca and Frankia was obtained after inoculation of young plant with a concentrated culture of the bacteria. Inoculation was performed in a medium depleted in nitrogen which favors the induction of nitrogen fixing symbiosis. For this study we considered two stages of symbiosis: - an early stage where inoculated roots were harvested 7 days after inoculation with the bacteria and compared to two controls (non-inoculated roots grown with or without nitrogen and harvested at the same time) - a late stage where nodules (nitrogen-fixing specific organs) were harvested 21 days after inoculation and compared to non-inoculated roots harvested on the day of inoculation (which is our reference time 0d). Three biological replicates were used for each condition.