Project description:Here we apply a metabolomics to study the interaction of two co-isolated model organisms, Xanthomonas retroflexus and Paenibacillus amylolyticus. When cultured in close proximity on agar plates Xanthomonas retroflexus induces a clear morphological response from Paenibacillus amylolyticus, leading to enhanced growth of Paenibacillus amylolyticus. Application of 2D spatial metabolomics shows how Xanthomonas retroflexus influences the chemical environment by production specific metabolites.
Project description:Nitrogen fixation is a highly energy-demanding process and highly regulated at multiple levels. The two major signals that regulate nitrogen fixation in most diazotrophs are oxygen and ammonia. In order to study the complex regulated mechanism and to highlight the complete nitrogen fixing system in genome level, here we present the transcriptional profiles of the nitrogen fixation genes of P.stutzeri A1501 in different growth conditions with a genome-wide DNA microarray. In this study, the three samples of "P.stutzeri A1501 treated with 0.1mM ammonia and 0.5% Oxygen tension","P.stutzeri A1501 treated with 0.1mM ammonia and 0.5% Oxygen tension-2" and "P.stutzeri A1501 treated with 0.1mM ammonia and 0.5% Oxygen tension-3" were three repeat experiments, while, the other three samples of "P.stutzeri A1501 treated with 20mM ammonia and 0.5% Oxygen tension-1", "P.stutzeri A1501 treated with 20mM ammonia and 0.5% Oxygen tension-2" and "P.stutzeri A1501 treated with 20mM ammonia and 0.5% Oxygen tension-3" were three repeat experiments. The gene expressions under these two growth phases were compared to investigate which genes' expression were effected by different ammonia concentrations. Keywords: nitrogen fixation, nitrogen repression
Project description:Our study revealed a synergistic effect between biological nitrogen fixation and current generation by G. sulfurreducens, providing a green nitrogen fixation alternative through shifting the nitrogen fixation field from energy consumption to energy production and having implications for N-deficient wastewater treatment.
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:Of all the essential nutrients, nitrogen is the one most often limiting for plant growth. Nitrogen can be taken up by plants in two ways. One possibility is through ammonium and nitrate, which are the predominate inorganic forms of nitrogen in soils. The second possibility is the uptake of air-born nitrogen through plant-associated mircoorganisms in root nodules. The majority of plants able to form such nitrogen-fixing root nodules are in the legume family Fabaceae. Here we present a third possibility – a new pathway, termed as nitric oxide (NO)-fixation pathway, which allows plants to fix atmospheric NO and to use it for better growth and development. We identified non-symbiotic hemoglobin class 1 (AtGLB1) and class 2 (AtGLB2) as key proteins of the NO-fixation pathway. In an NO enriched environment NO-fixation is enhanced considerably in plants overexpressing AtGLB1 or AtGLB2 genes. NO uptake resulted in four-fold higher nitrate levels in these plants compared to NO-treated wild-type plants. Correspondingly, the growth parameters like rosettes size and weight, vegetative shoot thickness and also seed yield were 25%, 40%, 30%, and 20% higher, respectively, in the overexpression lines in comparison to wild-type plants. Our results highlight the existence of a NO-fixing pathway in plants. We demonstrated that plant non-symbiotic hemoglobin proteins can fix atmospheric NO and convert it to nitrate, which is further introduced into the N-metabolism. We assume that our results might provide new insights into the field of crop science research and that the NO-fixation capability might serve as a new economically important breeding trait for enhancing biomass, fruit, and seed production. Modifying this pathway might be a promising approach for better and more environment-friendly supply of nitrogen. For example crop plant hemoglobin proteins could be improved for their NO-fixing capability and their expression levels could be increased.
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:Biological nitrogen fixation, the microbial reduction of atmospheric nitrogen to bioavailable ammonia, represents both a major limitation on biological productivity and a highly desirable engineering target for synthetic biology. However, the engineering of nitrogen fixation requires an integrated understanding of how the gene regulatory dynamics of host diazotrophs respond across sequence-function space of its central catalytic metalloenzyme, nitrogenase. Here, we interrogate this relationship by analyzing the transcriptome of Azotobacter vinelandii engineered with a phylogenetically inferred ancestral nitrogenase protein variant. The engineered strain exhibits reduced cellular nitrogenase activity but recovers wild-type growth rates following an extended lag period. We find that expression of genes within the immediate nitrogen fixation network is resilient to the introduced nitrogenase sequence-level perturbations. Rather the sustained physiological compatibility with the ancestral nitrogenase variant is accompanied by reduced expression of genes that support trace metal and electron resource allocation to nitrogenase. Our results spotlight gene expression changes in cellular processes adjacent to nitrogen fixation as productive engineering considerations to improve compatibility between remodeled nitrogenase proteins and engineered host diazotrophs. IMPORTANCE Azotobacter vinelandii is a key model bacterium for the study of biological nitrogen fixation, an important metabolic process catalyzed by nitrogenase enzymes. Here, we demonstrate that compatibilities between engineered A. vinelandii strains and nitrogenase variants can be modulated at the regulatory level. The engineered strain studied here responds by adjusting the expression of proteins involved in cellular processes adjacent to nitrogen fixation, rather than that of nitrogenase proteins themselves. These insights can inform future strategies to transfer nitrogenase variants to non-native hosts.
Project description:The transcriptional differences found during stationary-phase ammonium accumulation show a strong contrast between the deregulated (nifL disrupted) and wild-type strain, and to what was reported for the wild-type strain under exponential growth related to key processes involved in driving the process of nitrogen fixation in A. vinelandii. These results further illuminate a number of additional genes associated with siderophore synthesis, molybdate transfer and electron transfer that are likely associated with biological nitrogen fixation.