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Microaerobic lifestyle at nanomolar o2 concentrations mediated by low-affinity terminal oxidases in abundant soil bacteria

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  • Daniela Trojan, University of Vienna
  • ,
  • Emilio Garcia-Robledo, University of Cádiz
  • ,
  • Dimitri V. Meier, University of Vienna
  • ,
  • Bela Hausmann, University of Vienna, Medical University of Vienna
  • ,
  • Niels Peter Revsbech
  • Stephanie A. Eichorst, University of Vienna
  • ,
  • Dagmar Woebken, University of Vienna

High-affinity terminal oxidases (TOs) are believed to permit microbial respiration at low oxygen (O2) levels. Genes encoding such oxidases are widespread, and their existence in microbial genomes is taken as an indicator for microaerobic respiration. We combined respiratory kinetics determined via highly sensitive optical trace O2 sensors, genomics, and transcriptomics to test the hypothesis that high-affinity TOs are a prerequisite to respire micro- and nanooxic concentrations of O2 in environmentally relevant model soil organisms: Acidobacteria. Members of the Acidobacteria harbor branched respiratory chains terminating in low-affinity (caa3-type cytochrome c oxidases) as well as high-affinity (cbb3-type cytochrome c oxidases and/or bd-type quinol oxidases) TOs, potentially enabling them to cope with varying O2 concentrations. The measured apparent Km (Km(app)) values for O2 of selected strains ranged from 37 to 288 nmol O2 liter21, comparable to values previously assigned to low-affinity TOs. Surprisingly, we could not detect the expression of the conventional high-affinity TO (cbb3 type) at micro- and nanomolar O2 concentrations but detected the expression of low-affinity TOs. To the best of our knowledge, this is the first observation of microaerobic respiration imparted by low-affinity TOs at O2 concentrations as low as 1 nM. This challenges the standing hypothesis that a microaerobic lifestyle is exclusively imparted by the presence of high-affinity TOs. As low-affinity TOs are more efficient at generating ATP than high-affinity TOs, their utilization could provide a great benefit, even at low-nanomolar O2 levels. Our findings highlight energy conservation strategies that could promote the success of Acidobacteria in soil but might also be important for as-yet-unrevealed microorganisms.

Original languageEnglish
Article numbere00250-21
Publication statusPublished - Jul 2021

Bibliographical note

Publisher Copyright:
© 2021 Trojan et al.

    Research areas

  • Acidobacteria, Kinetics, Oxygen, Terminal oxidase, Transcriptomics

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