Genome-wide transcriptional responses of Nitrosomonas europaea to zinc
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ORIGINAL PAPER
Genome-wide transcriptional responses of Nitrosomonas europaea to zinc Sunhwa Park Æ Roger L. Ely
Received: 12 July 2007 / Revised: 24 November 2007 / Accepted: 4 December 2007 / Published online: 21 December 2007 Springer-Verlag 2007
Abstract Nitrosomonas europaea, a Gram-negative obligate chemolithoautotroph, participates in global nitrogen cycling by carrying out nitrification and derives energy for growth through oxidation of ammonia. In this work, the physiological, proteomic, and transcriptional responses of N. europaea to zinc stress were studied. The nitrite production rate and ammonia-dependent oxygen uptake rate of the cells exposed to 3.4 lM ZnCl2 decreased about 61 and 69% within 30 min, respectively. Two proteins were notably up regulated in zinc treatment and the mRNA levels of their encoding genes started to increase by 1 h after the addition of zinc. A total of 27 genes were up regulated and 30 genes were down regulated. Up-regulated genes included mercury resistance genes (merTPCAD), inorganic ion transport genes, oxidative stress genes, toxinantitoxin genes, and two-component signal transduction systems genes. merTPCAD was the highest up-regulated operon (46-fold). Down-regulated genes included the RubisCO operon (cbbO), biosynthesis (mrsA), and amino acid transporter. Keywords Nitrosomonas europaea 2-D SDS-PAGE Zinc cDNA microarray Quantitative reverse transcriptase-PCR
Communicated by Stuart Ferguson. S. Park R. L. Ely (&) Department of Biological and Ecological Engineering, Oregon State University, Corvallis, OR 97331, USA e-mail: [email protected]
Introduction Nitrosomonas europaea (ATCC19718) is an obligate chemolithoautotroph that obtains energy and reductant for growth from the oxidation of ammonia to nitrite through a two-step process (Hyman and Arp 1995). The two steps are carried out by ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO), respectively, as follows: NH3 þ O2 þ 2Hþ þ 2e ! NH2 OH þ H2 O þ ! NO 2 þ 5H þ 4e : The four electrons derived from hydroxylamine oxidation support both AMO activity and ATP synthesis. N. europaea belongs to the betaproteobacteria and contains a single circular chromosome of 2,812,094 bp with 2,460 predicted genes. Most of the genes in the 285 open reading frames related to active transport in N. europaea encode transporters of inorganic ions (Chain et al. 2003). Zinc is a vital catalytic component of seven enzymes, such as zinc metallopeptidase and zinc transporters, and of two zinc-based domains (termed ‘‘zinc fingers’’) in N. europaea. However, industrial developments have elevated zinc concentrations in some environments and zinc is regarded as a permanent contaminant because of its nondegradability (Pomposiello et al. 2001). Excessive zinc in wastewater can accumulate inside cells and may cause zinc cytotoxicity in two ways: (1) by binding with SH groups of proteins involved in electron transport systems and (2) by generating reactive oxygen species (HO• or HOO••) (Nies 1999; Outten and O’Halloran 200
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