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Inhibition and gene expression of Nitrosomonas europaea biofilms exposed to phenol and toluene

Authors

  • Ellen G. Lauchnor,

    1. School of Chemical, Biological and Environmental Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, Oregon 97331; telephone: 541-737-6895; fax: 541-737-3099
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  • Tyler S. Radniecki,

    1. School of Chemical, Biological and Environmental Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, Oregon 97331; telephone: 541-737-6895; fax: 541-737-3099
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  • Lewis Semprini

    Corresponding author
    1. School of Chemical, Biological and Environmental Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, Oregon 97331; telephone: 541-737-6895; fax: 541-737-3099
    • School of Chemical, Biological and Environmental Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, Oregon 97331; telephone: 541-737-6895; fax: 541-737-3099.
    Search for more papers by this author

Abstract

Pure culture biofilms of the ammonia-oxidizing bacterium Nitrosomonas europaea were grown in a Drip Flow Biofilm Reactor and exposed to the aromatic hydrocarbons phenol and toluene. Ammonia oxidation rates, as measured by nitrite production in the biofilms, were inhibited 50% when exposed to 56 µM phenol or 100 µM toluene, while 50% inhibition of suspended cells occurred at 8 µM phenol or 20 µM toluene. Biofilm-grown cells dispersed into liquid medium and immediately exposed to phenol or toluene experienced similar inhibition levels as batch grown cells, indicating that mass transfer may be a factor in N. europaea biofilm resistance. Whole genome microarray analysis of gene expression was used to detect genes up-regulated in biofilms during toluene and phenol exposure. Two genes, a putative pirin protein (NE1545) and a putative inner membrane protein (NE1546) were up-regulated during phenol exposure, but no genes were up-regulated during toluene exposure. Using qRT-PCR, up-regulation of NE1545 was detected in biofilms and suspended cells exposed to a range of phenol concentrations and levels of inhibition. In the biofilms, NE1545 expression was up-regulated an average of 13-fold over the range of phenol concentrations tested, and was essentially independent of phenol concentration. However, the expression of NE1545 in suspended cells increased from 20-fold at 7 µM phenol up to 80-fold at 30 µM phenol. This study demonstrates that biofilms of N. europaea are more resistant than suspended cells to inhibition of ammonia oxidation by phenol and toluene, even though the global transcriptional responses to the inhibitors do not differ in N. europaea between the suspended and attached growth states. Biotechnol. Bioeng. 2011; 108:750–757. © 2010 Wiley Periodicals, Inc.

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