title: Oxygen-dependent autoaggregation in Shewanella oneidensis MR-1.
abstract: In aerobic chemostat cultures maintained at 50% dissolved O(2) tension (3.5 mg l(-1) dissolved O(2)), Shewanella oneidensis strain MR-1 rapidly aggregated upon addition of 0.68 mM CaCl(2) and retained this multicellular phenotype at high dilution rates. Confocal microscopy analysis of the extracellular matrix material contributing to the stability of the aggregate structures revealed the presence of extracellular DNA, protein and glycoconjugates. Upon onset of O(2)-limited growth (dissolved O(2) below detection) however, the Ca(2+)-supplemented chemostat cultures of strain MR-1 rapidly disaggregated and grew as motile dispersed cells. Global transcriptome analysis comparing aerobic aggregated to O(2)-limited unaggregated cells identified genes encoding cell-to-cell and cell-to-surface adhesion factors whose transcription increased upon exposure to increased O(2) concentrations. The aerobic aggregated cells also revealed increased expression of putative anaerobic electron transfer and homologues of metal reduction genes, including mtrD (SO1782), mtrE (SO1781) and mtrF (SO1780). Our data indicate that mechanisms involved in autoaggregation of MR-1 are dependent on the function of pilD gene which encodes a putative prepilin peptidase. Mutants of S. oneidensis strain MR-1 deficient in PilD and associated pathways, including type IV and Msh pili biogenesis, displayed a moderate increase in sensitivity to H(2)O(2). Taken together, our evidence indicates that aggregate formation in S. oneidensis MR-1 may serve as an alternative or an addition to biochemical detoxification to reduce the oxidative stress associated with production of reactive oxygen species during aerobic metabolism while facilitating the development of hypoxic conditions within the aggregate interior.
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA99352, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: McLean
authors.forename: G E
authors.initials: GE
authors.lastname: Pinchuk
authors.forename: O V
authors.initials: OV
authors.lastname: Geydebrekht
authors.forename: C L
authors.initials: CL
authors.lastname: Bilskis
authors.forename: B A
authors.initials: BA
authors.lastname: Zakrajsek
authors.forename: E A
authors.initials: EA
authors.lastname: Hill
authors.forename: D A
authors.initials: DA
authors.lastname: Saffarini
authors.forename: M F
authors.initials: MF
authors.lastname: Romine
authors.forename: Y A
authors.initials: YA
authors.lastname: Gorby
authors.forename: J K
authors.initials: JK
authors.lastname: Fredrickson
authors.forename: A S
authors.initials: AS
authors.lastname: Beliaev
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D020592:Shewanella / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D010100:Oxygen