title: Metabolic adaptations of Azospirillum brasilense to oxygen stress by cell-to-cell clumping and flocculation.
abstract: The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Amber N
authors.initials: AN
authors.lastname: Bible
authors.affiliation: Genome Science and Technology Graduate Program, The University of Tennessee, Knoxville, Tennessee, USA Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
authors.forename: Gurusahai K
authors.initials: GK
authors.lastname: Khalsa-Moyers
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Tanmoy
authors.initials: T
authors.lastname: Mukherjee
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Calvin S
authors.initials: CS
authors.lastname: Green
authors.affiliation: Genome Science and Technology Graduate Program, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Mishra
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Purcell
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Aksenova
authors.affiliation: Genome Science and Technology Graduate Program, The University of Tennessee, Knoxville, Tennessee, USA Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Hurst
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA Genome Science and Technology Graduate Program, The University of Tennessee, Knoxville, Tennessee, USA galexan2@utk.edu.
authors.forename: Gladys
authors.initials: G
authors.lastname: Alexandre
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D015806:Azospirillum brasilense / Q000235:genetics / Q000378:metabolism*; D001422:Bacterial Adhesion / Q000502:physiology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002853:Chromatography, Liquid; D004251:DNA Transposable Elements / Q000235:genetics; D005427:Flocculation; D010100:Oxygen / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D013312:Stress, Physiological / Q000502:physiology*; D053719:Tandem Mass Spectrometry
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D010100:Oxygen