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Solvent Stress Response of the Denitrifying Bacterium "Aromatoleum aromaticum" Strain EbN1 ^,

Kathleen Trautwein,^1,2, Simon Kühner,^2, Lars Wöhlbrand,² Thomas Halder,³ Kenny Kuchta,⁴ Alexander Steinbüchel,⁴ and Ralf Rabus^1,2*

Institute of Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Carl-von-Ossietzky Str. 9-11, D-26111 Oldenburg, Germany,¹ Max Planck Institute for Marine Microbiology, Celsiusstr. 1, D-28359 Bremen, Germany,² TopLab GmbH, Fraunhoferstr. 18a, D-82152 Martinsried, Germany,³ Institute for Molecular Microbiology and Biotechnology, Westfälische Wilhelms University of Münster, Corrensstr. 3, D-48149 Münster, Germany⁴

Received 23 October 2007/ Accepted 28 January 2008

The denitrifying betaproteobacterium "Aromatoleum aromaticum" strain EbN1 degrades several aromatic compounds, including ethylbenzene, toluene, p-cresol, and phenol, under anoxic conditions. The hydrophobicity of these aromatic solvents determines their toxic properties. Here, we investigated the response of strain EbN1 to aromatic substrates at semi-inhibitory (about 50% growth inhibition) concentrations under two different conditions: first, during anaerobic growth with ethylbenzene (0.32 mM) or toluene (0.74 mM); and second, when anaerobic succinate-utilizing cultures were shocked with ethylbenzene (0.5 mM), toluene (1.2 mM), p-cresol (3.0 mM), and phenol (6.5 mM) as single stressors or as a mixture (total solvent concentration, 2.7 mM). Under all tested conditions impaired growth was paralleled by decelerated nitrate-nitrite consumption. Additionally, alkylbenzene-utilizing cultures accumulated poly(3-hydroxybutyrate) (PHB) up to 10% of the cell dry weight. These physiological responses were also reflected on the proteomic level (as determined by two-dimensional difference gel electrophoresis), e.g., up-regulation of PHB granule-associated phasins, cytochrome cd₁ nitrite reductase of denitrification, and several proteins involved in oxidative (e.g., SodB) and general (e.g., ClpB) stress responses.

Published ahead of print on 8 February 2008.

Supplemental material for this article may be found at http://aem.asm.org/.

These authors contributed equally to this work.