Project description:Nitrogen fixation is an important metabolic process carried out by microorganisms, which converts molecular nitrogen into inorganic nitrogenous compounds such as ammonia (NH3). These nitrogenous compounds are crucial for biogeochemical cycles and for the synthesis of essential biomolecules, i.e. nucleic acids, amino acids and proteins. Azotobacter vinelandii is a bacterial non-photosynthetic model organism to study aerobic nitrogen fixation (diazotrophy) and hydrogen production. Moreover, the diazotroph can produce biopolymers like alginate and polyhydroxybutyrate (PHB) that have important industrial applications. However, many metabolic processes such as partitioning of carbon and nitrogen metabolism in A. vinelandii remain unknown to date.
Genome-scale metabolic models (M-models) represent reliable tools to unravel and optimize metabolic functions at genome-scale. M-models are mathematical representations that contain information about genes, reactions, metabolites and their associations. M-models can simulate optimal reaction fluxes under a wide variety of conditions using experimentally determined constraints. Here we report on the development of a M-model of the wild type bacterium A. vinelandii DJ (iDT1278) which consists of 2,003 metabolites, 2,469 reactions, and 1,278 genes. We validated the model using high-throughput phenotypic and physiological data, testing 180 carbon sources and 95 nitrogen sources. iDT1278 was able to achieve an accuracy of 89% and 91% for growth with carbon sources and nitrogen source, respectively. This comprehensive M-model will help to comprehend metabolic processes associated with nitrogen fixation, ammonium assimilation, and production of organic nitrogen in an environmentally important microorganism.
Project description:Although N2 fixation can occur in free-living cyanobacteria, the unicellular endosymbiotic cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN-A) is considered to be a dominant N2-fixing species in marine ecosystems. Four UCYN-A sublineages are known from partial nitrogenase (nifH) gene sequences. However, few studies have investigated their habitat preferences and regulation by their respective hosts in open-ocean versus coastal environments. Here, we compared UCYN-A transcriptomes from oligotrophic open-ocean versus nutrient-rich coastal waters. UCYN-A1 metabolism was more impacted by habitat changes than UCYN-A2. However, across habitats and sublineages genes for nitrogen fixation and energy production were highly transcribed. Curiously these genes, critical to the symbiosis for the exchange of fixed nitrogen for fixed carbon, maintained the same schedule of diel expression across habitats and UCYN-A sublineages, including UCYN-A3 in the open-ocean transcriptomes. Our results undersore the importance of nitrogen fixation in UCYN-A symbioses across habitats, with consequences for community interaction and global biogeochemical cycles.
Project description:Here we have compared adult wildtype (N2) C. elegans gene expression when grown on different bacterial environments/fod sources in an effort to model naturally occuring nematode-bacteria interactions at the Konza Prairie. We hypothesize that human-induced changes to natural environments, such as the addition of nitrogen fertalizer, have effects on the bacterial community in soils and this drives downstream changes in the structure on soil bacterial-feeding nematode community structure. Here we have used transcriptional profiling to identify candidate genes involved in the interaction of nematodes and bacteria in nature.
Project description:Resendis-Antonio2007 - Genome-scale metabolic
network of Rhizobium etli (iOR363)
This model is described in the article:
Metabolic reconstruction and
modeling of nitrogen fixation in Rhizobium etli.
Resendis-Antonio O, Reed JL,
Encarnación S, Collado-Vides J, Palsson BØ.
PLoS Comput. Biol. 2007 Oct; 3(10):
1887-1895
Abstract:
Rhizobiaceas are bacteria that fix nitrogen during symbiosis
with plants. This symbiotic relationship is crucial for the
nitrogen cycle, and understanding symbiotic mechanisms is a
scientific challenge with direct applications in agronomy and
plant development. Rhizobium etli is a bacteria which provides
legumes with ammonia (among other chemical compounds), thereby
stimulating plant growth. A genome-scale approach, integrating
the biochemical information available for R. etli, constitutes
an important step toward understanding the symbiotic
relationship and its possible improvement. In this work we
present a genome-scale metabolic reconstruction (iOR363) for R.
etli CFN42, which includes 387 metabolic and transport
reactions across 26 metabolic pathways. This model was used to
analyze the physiological capabilities of R. etli during stages
of nitrogen fixation. To study the physiological capacities in
silico, an objective function was formulated to simulate
symbiotic nitrogen fixation. Flux balance analysis (FBA) was
performed, and the predicted active metabolic pathways agreed
qualitatively with experimental observations. In addition,
predictions for the effects of gene deletions during nitrogen
fixation in Rhizobia in silico also agreed with reported
experimental data. Overall, we present some evidence supporting
that FBA of the reconstructed metabolic network for R. etli
provides results that are in agreement with physiological
observations. Thus, as for other organisms, the reconstructed
genome-scale metabolic network provides an important framework
which allows us to compare model predictions with experimental
measurements and eventually generate hypotheses on ways to
improve nitrogen fixation.
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MODEL1507180006.
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Project description:The objective of this study was to identify the different functional genes involved in key biogeochemical cycles in the low Arctic regions. Understanding the microbial diversity in the Arctic region is an important step to determine the effects of climate change on these areas.
Project description:<p>Biological nitrogen fixation by free-living bacteria and rhizobial symbiosis with legumes plays a key role in sustainable crop production. Here, we study how different crop combinations influence the interaction between peanut plants and their rhizosphere microbiota via metabolite deposition and functional responses of free-living and symbiotic nitrogen-fixing bacteria. Based on a long-term (8 year) diversified cropping field experiment, we find that peanut co-cultured with maize and oilseed rape lead to specific changes in peanut rhizosphere metabolite profiles and bacterial functions and nodulation. Flavonoids and coumarins accumulate due to the activation of phenylpropanoid biosynthesis pathways in peanuts. These changes enhance the growth and nitrogen fixation activity of free-living bacterial isolates, and root nodulation by symbiotic Bradyrhizobium isolates. Peanut plant root metabolites interact with Bradyrhizobium isolates contributing to initiate nodulation. Our findings demonstrate that tailored intercropping could be used to improve soil nitrogen availability through changes in the rhizosphere microbiome and its functions.</p>
Project description:The objective of this study was to identify the different functional genes involved in key biogeochemical cycles in thehigh Arctic regions. Understanding the microbial diversity in the Arctic region is an important step to determine the effects of climate change on these areas.