Influence of p -cresol on the proteome of the autotrophic nitrifying bacterium Nitrosomonas eutropha C91
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Original Paper
Influence of p‑cresol on the proteome of the autotrophic nitrifying bacterium Nitrosomonas eutropha C91 H. Kjeldal · L. Pell · A. Pommerening‑Röser · J. L. Nielsen
Received: 10 March 2014 / Revised: 4 April 2014 / Accepted: 9 April 2014 / Published online: 29 April 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract In this study, the effect of the organic micropollutant and known inhibitor of nitrification, p-cresol, was investigated on the metabolism of the ammonia oxidizing bacteria (AOB) Nitrosomonas eutropha C91 using MSbased quantitative proteomics. Several studies have demonstrated that AOB are capable of biotransforming a wide variety of aromatic compounds making them suitable candidates for bioremediation, yet the underlying molecular mechanisms are poorly described. The effect of two different concentrations of the aromatic micropollutant p-cresol (1 and 10 mg L−1) on the metabolism of N. eutropha C91, relative to a p-cresol absent control, was investigated. Though the rate of nitrification in N. eutropha C91 appeared essentially unaffected at both concentrations of p-cresol relative to the control, the expressional pattern of the proteins of N. eutropha C91 changed significantly. The presence of p-cresol resulted in the repressed expression of several key proteins related to N-metabolism, seemingly impairing energy production in N. eutropha C91, contradicting the observed unaltered rates of nitrification. However, the expression of proteins of the TCA cycle and proteins Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-014-0985-z) contains supplementary material, which is available to authorized users. H. Kjeldal · J. L. Nielsen (*) Departments of Biotechnology, Chemistry and Environmental Engineering, Center for Microbial Communities, Aalborg University, Aalborg, Denmark e-mail: [email protected] L. Pell · A. Pommerening‑Röser Biocenter Klein Flottbek, Microbiology und Biotechnology, University of Hamburg, Hamburg, Germany
related to xenobiotic degradation, including a p-cresol dehydrogenase, was found to be stimulated by the presence of p-cresol. This indicates that N. eutropha C91 is capable of degrading p-cresol and that it assimilates degradation intermediates into the TCA cycle. The results reveal a pathway for p-cresol degradation and subsequent entry point in the TCA cycle in N. eutropha C91. The obtained data indicate that mixotrophy, rather than cometabolism, is the major mechanism behind p-cresol degradation in N. eutropha C91. Keywords AOB · Mixotrophy · p-Cresol · Proteomics
Introduction Ammonia oxidizing bacteria (AOB) are key players in the nitrogen cycle and responsible for oxidizing ammonia (NH3) into nitrite (NO2−) under aerobic conditions. AOB are widely regarded as chemolithoautotrophs with the ability to utilize ammonia and carbon dioxide as their main energy and carbon sources, respectively (Matin 1978). Ammonia oxidation is carried out by the successive oxidation of ammonia into hydrox
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