Environ Sci Pollut Res (2013) 20:803–811 DOI 10.1007/s11356-012-1280-7 RESEARCH ARTICLE Mechanisms of toxicity of triphenyltin chloride (TPTC) determined by a live cell reporter array Guanyong Su & Xiaowei Zhang & Jason C. Raine & Liqun Xing & Eric Higley & Markus Hecker & John P. Giesy & Hongxia Yu Received: 8 August 2012 / Accepted: 24 September 2012 / Published online: 6 November 2012 # Springer-Verlag Berlin Heidelberg 2012 Abstract Triphenyltin chloride (TPTC), which has been extensively used in industry and agriculture, can occur at concentrations in the environment sufficient to be toxic. Here, potency of TPTC to modulate genes in a library containing 1,820 modified green fluorescent protein (GFP)-expressing promoter reporter vectors constructed from Escherichia coli K12 strains was determined. Exposure to TPTC resulted in 22 (fold change > 2) or 71 (fold change > 1.5) differentially expressed genes. The no observed transcriptional effect (NOTEC) and median transcriptional effect concentrations (TEC50) were determined to be 0.036 and 0.45 mg/L in E. coli. These responses were 1,230 and 97 times more sensitive than the acute median effect concentration (EC50) required to inhibit growth of cells, which demonstrated that this live cell array represents a sensitive method to assess toxic potency of chemicals. The 71 differentially expressed genes could be classified into seven functional groups. Of all the altered genes, three groups which encoded for catalytic enzymes, regulatory proteins, and structural proteins accounted for 28 %, 18 %, and 14 % of all altered genes, respectively. The pattern of differential expression observed during this study was used to elucidate the mechanism of toxicity of TPTC. To determine potential relationships among genes that were changed greater than 2.0-fold by exposure to TPTC, a correlation network analysis was constructed, and four genes were related to aroH, which is the primary target for metabolic regulation of aromatic biosynthesis by feedback inhibition in bacteria. The genes rnC, cld, and glgS were selected as potential biomarkers for TPTC, since their expression was more than 2.0-fold greater after exposure to TPTC. Keywords High throughput . NOTEC . Biomarker . Correlation network . Toxicity assessment . Bacterial . Genomics . Organotin Responsible editor: Philippe Garrigues Electronic supplementary material The online version of this article (doi:10.1007/s11356-012-1280-7) contains supplementary material, which is available to authorized users. G. Su : X. Zhang : L. Xing : J. P. Giesy : H. Yu State Key Laboratory of Pollution Control and Resource Reuse & School of the Environment, Nanjing University, Nanjing, China J. P. Giesy Department of Biomedical Veterinary Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada G. Su : J. C. Raine : E. Higley : M. Hecker : J. P. Giesy Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada J. P. Giesy Department of Biology and Chemistry and State Key Laboratory in Marine Pollution, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China M. Hecker School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada X. Zhang (*) : H. Yu (*) School of the Environment, Nanjing University, Nanjing 210089, China e-mail: howard50003250@yahoo.com e-mail: yuhx@nju.edu.cn 804 Introduction Organotin compounds are widely used with a worldwide production that has increased almost tenfold over the past 40 years (Liu et al. 2006). These compounds are extensively used in industry and agriculture as biocides, fungicides, antifouling agents in boat paint, wood preservatives, catalysts, and stabilizers for polyvinylchloride polymers (Fent and Muller 1991; Grote et al. 2007; Sano et al. 2010). Of the organotin compounds, triphenyltin chloride (TPTC) is one of the most potent. Concentrations less than 40 ngTPTC/ml can affect the immune system of cultivated clams (Tapes philippinarum) (Cima et al. 1998) and enhance histone acetyltransferase activity, which is a type endocrine-disruption (Osada et al. 2005). TPTC can also inhibit gap junctional intercellular communication in WB-F344 rat liver epithelial cells (Lee et al. 2010) and cause loss of post-implantation of embryos, failure to implant, and effects on body mass, size, and structure of testicles and lesser fertility of Holtzmann rats (Ema 2000). Because of bio-concentration and accumulation potentials (Horiguchi et al. 1997; Shim et al. 2000), TPTC could also pose a risk to human health through dietary exposure. While it has been established that TPTC is more toxic than some other pollutants, the mechanisms by which it causes toxicity remain mostly unknown. Genome-wide transcriptional investigations using whole cell arrays is a useful toxicogenomic approach to characterize modes of toxic action of chemicals (Zhang et al. 2011; Su et al. 2012). Whole cell arrays consist of an assortment of genetically engineered microorganisms tailored to respond to activation of specific promoters. Fusion of stress promoters to reporter genes (such as fluorescent proteins) is the basic concept for detection of cellular signaling (Elad et al. 2010). Compared with microarray technology, whole cell arrays avoid complex protocols of pre-treatment and highcost experimental materials, have fewer interferences, and can provide temporal resolution (Onnis-Hayden et al. 2009). Furthermore, the short testing time (less than 3 h) makes live cell arrays rapid, economical, high-throughput biosensor systems for detecting toxicity and determining effects on specific signaling pathways. Consequently, this assay is not specific to bacteria and can represent responses of systems that are conserved in multiple organisms, including metazoans (Zhang et al. 2011). Here, toxicity of TPTC was assessed by application of a comprehensive cell array of transcriptional fusions of GFP to each of 1,820 different gene promoters in Escherichia coli K12. Profiles of concentration- and time-dependent expression of genes caused by TPTC were obtained over 3-h exposures to 0.1, 1, or 10 mg TPTC/L. All altered genes were classified into seven groups according to their known function (Supplementary Table 1), and the pattern of which was hypothesized to be indicative of the specific molecular Environ Sci Pollut Res (2013) 20:803–811 signaling pathways affected by exposure to TPTC. Based on these profiles of gene expression, a correlation network was generated to elucidate potential correlations of differentially expressed molecular pathways. Materials and methods Microbial live cell array The microbial promoter collection was produced by researchers at the Weizmann Institute of Science (Rehovot, Israel) and includes more than 1,900, out of 2,500 promoters in the entire genome of E. coli K12 strain MG1655 (Zaslaver et al. 2006). Each of the reporter strains is coupled with a bright, fast-folding GFP fused to a fulllength copy of an E. coli promoter in a low-copy plasmid. This enables measurement of gene expression within minutes with high accuracy and reproducibility. All clones were grown at 37 °C in lysogeny broth (LB)–Lennox media plus 25 mg/L kanamycin. Exposure to TPTC Triphenyltin chloride was purchased from Sigma Aldrich (#245712, St. Louis, MO, USA). A TPTC stock solution (20,000 mg/L) was prepared in dimethyl sulfoxide (DMSO), and other stock solutions were made by serial dilution with DMSO. Chemical-induced effects on growth of cells were assessed by measuring optical density (OD) at 600 nm by a Fluostar OPTIMA microplate reader (BMG Labtech, Offenburg, Germany). For each concentration, three replications were conducted. Specifically, growth and division of E. coli was determined after 4 h of incubation at 37 °C. The OD600 value is the most commonly used to estimate the E. coli cell density and corresponds with cell number in a given E. coli culture volume (Luo et al. 2011; Su et al. 2012). To measure expression of genes, assay plates were prepared by adding 72 μL of LB medium to each well in black 384-well optical bottom plates (NUNC, Rochester, NY, USA). E. coli strains were inoculated in the 384-well plate from a 96-well stock plate by disposable replicators (Genetix, San Jose, CA, USA). Cells were incubated at 37°C for a 2.5 h in 384-well plates, and then 3.8 μL of DMSO (solvent control) or TPTC stock solutions were added into individual wells of the 384well plates to make final concentrations of 0, 0.1, 1, or 10 mg TPTC/L. GFP intensity in each well was consecutively monitored every 10 min during 3 h by use of the Fluostar OPTIMA 120 microplate reader (excitation/emission, 545 nm/590 nm). Effects of TPTC on growth of cells were assessed by OD measurement prior to the promoter reporter assay. None of the three concentrations of TPTC caused significant effects on growth of cells during 10 h of exposure. Environ Sci Pollut Res (2013) 20:803–811 805 Data analyses All data analyses have been described previously (Zhang et al. 2011; Su et al. 2012). To select the promoter reporters that were significantly differentially expressed in response to exposure with TPTC, a linear regression model was applied. The response measured as GFP fluorescence intensity was fitted to a function of time for each promoter reporter strain. Classification and visualization of the gene expression were derived by ToxClust (Zhang et al. 2009). Determination of NOTEC The No Observed Transcriptional Effect Concentration (NOTEC) was calculated based on the number of promoter strains in the library of 1,820 genes that were significantly altered by TPTC. The No Observable Effect Concentration (NOEC) based on inhibition of growth by TPTC was determined. Then, the percentage of genes differentially expressed at different concentrations relative to the NOEC was calculated. Finally, a generalized linear binomial model was used to assess the concentration-dependent response curve of the percentage of the differentially expressed genes. The NOTEC was calculated as the maximum concentration of TPTC at which less than 5 % of the genes were differentially expressed upon chemical exposure compared with control (Su et al. 2012). Pathway analysis Lists of genes were developed for further analysis based on statistical significance and 1.5- or 2.0-fold change cutoffs. Differentially expressed genes were classified into seven groups based on their biological functions (www.ecogene.org, www.geneontology.org, and www.ecoliwiki.net; Supplementary Table 1). Correlation network analyses were conducted using the “GeneNet” package by R software (http://cran.r-project.org/ web/packages/GeneNet/). This method was used for analyzing gene expression (time series) data with focus on the inference of gene networks (Opgen-Rhein and Strimmer 2007). Results Inhibition of E. coli growth by TPTC TPTC inhibited growth of E. coli cells in a concentrationdependent manner (Fig. 1). The median effect concentration (EC50), NOEC, and lowest observed effect concentration of TPTC on cell growth were 43.7, 10.0, and 20.0 mg/L, respectively. Three concentrations, 0.1, 1, and 10 mg/L, were selected as exposure concentrations to assess the effects of TPTC on transcriptional expression profiles of E. coli. At these Fig. 1 Inhibition profile of E. coli growth by different concentrations of TPTC (data points were shown with mean values of three replications) concentrations, cell growth would not be affected. The NOEC was included to enable determination of the NOTEC. Gene expression profiles Expression of genes by the microbial reporter strains was modulated by TPTC in a time- and concentration-dependent manner. Exposure to TPTC resulted in fewer upregulated promoter strains than downregulated strains during the 3h exposure for genes selected by both the 1.5-fold (Fig. 2b) and 2.0-fold cut-offs (Fig. 2a). Of the 22 promoter reporter strains selected using a 2.0-fold cut-off, 2 and 20 strains were up- and downregulated, respectively. Of the 71 promoter reporter strains selected by application of a 1.5-fold cut-off, the greatest downregulation of as much as eightfold relative to the controls was observed for rrnC. Furthermore, this gene was separated from all other groups when data was subjected to analysis by ToxClast. Other than rrnC, expression of 16 and 54 genes were up- and downregulated, respectively (Fig. 2b). Alteration of gene expression by TPTC was concentrationdependent. Using a 2.0-fold change as a cut-off, exposure to 0.1, 1.0, or 10 mg, TPTC/L significantly altered expression of 2, 6, and 21 promoters, respectively. Only one strain was responsive to all three concentrations (Fig. 3). Of the 1,820 genes, 71 were differentially expressed with a maximum absolute fold change of at least 1.5 (Fig. 3). Among those genes, 17, 33, and 71 promoters were differentially expressed after exposure to 0.1, 1.0, or 10 mg TPTC/L, respectively, and 17 strains were responsive to all three concentrations. Exposure to 0.1 or 1.0 mg TPTC/L resulted in one gene, yhhY, being completely different from those modulated by exposure to 10 mg TPTC/L (Fig. 3). Determination of no observed transcriptional effect concentration Ratios of differentially expressed genes were 24 %, 47 %, and 100 % after exposure to 0.1, 1.0, or 10 mg 806 a 10 mg/L 1 mg/L 0.1 mg/L Conc. Fold Change 30 2 1 0.5 0.2 0 0.1 Fig. 2 Real-time gene expression profiles of differentially expressed gens in E. coli after exposure to 0.1, 1.0, or 10 mg TPTC/L as represented by the lower, middle, and upper bands in each gene column, respectively. Classification and visualization of the gene expression were derived by ToxClust. Dissimilarity between genes was calculated by the Manhattan distance between the gene expressions at all the concentration versus time combinations. Fold change of gene expression is indicated by color gradient, and the time course of expression changes is indicated from left to right. a Clustering of the timedependent expression of the TPTC altered genes selected by 2.0-fold change cut-off. b Clustering of the timedependent expression of the TPTC altered genes selected by 1.5-fold change cut-off Environ Sci Pollut Res (2013) 20:803–811 60 90 120 Time (min) 150 180 rmf skp ybcW lacZ yjdI mglB insA_7 menG uspF yifE 11 cld glgS wrbA add galU aqpZ mcrA yhhY yhcG rrnC serB aroH TPTC/L, respectively. The NOTEC was 0.036 mg TPTC/ L, a concentration at which fewer than 5 % of genes were differentially expressed relative to controls. The median transcriptional effect concentration (TEC50) was 0.45 mg TPTC/L. In previous publications, acute toxicity of TPTC ranged from 2.0 to 4,455 μg/L in nine aquatic species that included algae, fish, mollusks, worms, daphnids, and mysid shrimp (Fig. 4) (Goel and Prasad 1978; Goel and Srivastava 1981; Wong et al. 1982; Devries et al. 1991; Nagase et al. 1991; Fargasova 2002, 1997). Of these species, green algae (Ankistrodesmusfalcatus ssp. acicul) were the most sensitive species with an EC50 of 2.0 μg TPTC/L. Based on effects of TPTC on cell growth, E. coli was less sensitive than all other species and endpoints (Supplementary Table 3). However, the transcriptional endpoints, NOTEC and TEC50, in E. coli measured in this study were 1,230- and 97-fold more sensitive than the acute EC50 for inhibition of cell growth. Aligned onto the sensitive distribution curve of aquatic species, the NOTEC and TEC50 are equivalent to the 47th and 74th centile species, respectively. Classification of differentially expressed genes All differentially expressed genes were classified into one of seven groups: enzyme (pepE, aroH, serB, add, gcvT, lacZ, cysK, serA, dcd, dmsA, ligB, fpr, galU, gadB, metA, icd, lipA, cueO, aroK, and ttdA), regulatory protein (cysB, cspD, ftsK, gadX, phoP, mcrA, rmf, rsd, wrbA, fdhD, flgM, manX, and cld), structural protein (rpsT, rpsU, mglB, ytfF, b1403, ompC, ompA, skp, osmC, and aqpZ), rRNA or tRNA (argW, rrnB, rrnD, and rrnC), stress responsive pathway (evgA, uspB, uspA), amino acids formation (menG), and unclear function (yfbV, mntR, yhgF, yjdI, yhcG, yafK, insA_7, yaiE, b3007, yhhY, yeaU, glgS, proQ, yedW, yedP, ymcC, yfiE, uspF, yifE, and ybcW), which accounted for 28 %, 18 %, 14 %, 6 %, 4 %, 1 %, and 28 % of the 71 genes altered by TPTC, respectively. Among these differentially expressed genes, 22 (31 % of 71) genes’ fold change was greater than 2.0 (Supplementary Table 4). Correlation network A correlation network was constructed to analyze highdimensional data from E. coli gene expression (fold Environ Sci Pollut Res (2013) 20:803–811 Fig. 2 (continued) 807 b 2 1 0.5 0.2 0.1 Fold Change b1403 fdhD ymcC mntR yedP yaiE gadX add dcd argW icd flgM yafK cysB yjdI lacZ ttdA yhhY yfiE osmC serA ftsK uspB mglB insA_7 ytfF yeaU uspA pepE yfbV cueO ligB gcvT yhgF metA phoP fpr b3007 cysK serB aroH wrbA skp menG cld glgS rmf ybcW aqpZ mcrA rrnD gadB manX proQ uspF yifE ompA yedW lipA rpsU cspD evgA rsd ompC aroK rrnB rpsT yhcG dmsA galU rrnC change >2) after exposure to TPTC based on graphical Gaussian models (Opgen-Rhein and Strimmer 2007) (Fig. 5). From their expression profiles after 3 h, correlation coefficients between each two related nodes (genes) were calculated. Six of the 22 genes that were altered by more than 2.0-fold were directly related with aroH, and four genes (wrbA, cld, rmf, and glgs) exhibited significant correlations with aroH protein (r>0.89). And four genes (uspF, aqpZ, galU, aroH) were associated with rrnC. Functions of these genes are given in Supplementary Table 1. Fig. 3 Concentration-dependent promoter activity of reporter strains in TPTC exposure. (Venn diagram displayed the differentially expressed genes selected by 1.5- or 2.0-fold change cut-off at three different TPTC concentrations including 0.1, 1, and 10 mg/L, which were marked with red, green, and blue, respectively) Fig. 4 Species sensitivity distribution using the ecotoxicity data of TPTC and the data acquired in the present study. Probit model was fitted for different species. NOTEC and TEC 50 are represented as blue and red asterisks on the fitted curve, respectively. Detailed ecotoxicity data are available in the Supplementary Table 2) 808 Fig. 5 Sparse graphical Gaussian model for 22 genes inferred from an E. coli live cell array data set with 19 data points Discussion The fact that transcriptional endpoints measured in this study were more sensitive than the acute EC50 based on inhibition of growth of cells demonstrated that effects of TPTC on transcription as expressed by the NOTEC represent a sensitive endpoint to assess toxicity of this chemical. This result is consistent with previous reports that have demonstrated that the NOTEC is more sensitive than conventional endpoints, since it reflects sub-lethal and molecular level responses to a toxicant (Lobenhofer et al. 2004; Poynton et al. 2008). The relatively inexpensive live cell array could provide a sensitive tool to assess the toxicity of environmental chemicals in a short time (3 h). Future studies should evaluate the sensitivity of live cell array relative to several commonly used test species for additional chemicals. The gene expression profile suggested that TPTC can cause toxicity to E. coli through modulation of enzymes in biochemical reactions, including pepE, aroH, serB, add, gcvT, lacZ, cysK, serA, dcd, dmsA, ligB, fpr, galU, gadB, metA, icd, lipA, cueO, aroK, and ttdA, formation of regulatory proteins including cysB, cspD, ftsK, gadX, phoP, mcrA, rmf, rsd, wrbA, fdhD, flgM, manX, and cld, and structural proteins, including rpsT, rpsU, mglB, ytfF, b1403, ompC, ompA, skp, osmC, and aqpZ, rRNA or tRNA, including argW, rrnB, rrnD, and rrnC, stress responsive pathways, evgA, uspB, and uspA, and formation of amino acids (menG). To our knowledge, this is the first report using the E. coli whole cell assay to assess toxicity of TPTC. However, the toxic action of TPTC can be grouped into four general categories: (1) effects on immune function (Nishida et al. 1990), (2) Environ Sci Pollut Res (2013) 20:803–811 clastogens (Sasaki et al. 1994), (3) cytotoxicity (Snoeij et al. 1985), and (4) inhibition of intercellular gap junctions. Modulation of enzymes in biochemical reactions might be one of the most important TPTC-induced toxic pathways, since genes falling into this functional group accounted for 28 % of the total differentially expressed genes. After exposure to TPTC, 19 enzymes were altered, including αaspartyldipeptidase (pepE), 3-deoxy-D-arabino-heptulosonate-7- phosphate synthase (aroH), 3-phosphoserine phosphatase (serB), adenosine deaminase (add), aminomethyltransferase (gcvT), β-galactosidase (lacZ), cysteine synthase A (cysK), D -3-phosphoglycerate dehydrogenase (serA), deoxycytidine triphosphate deaminase (dcd), dimethyl sulfoxidereductase (dmsA), DNA ligase (ligB), ferredoxin-NADP reductase (fpr), glucose-1-phosphate uridylyltransferase (galU), glutamate decarboxylase B subunit (gadB), homoserinetranssuccinylase (icd), isocitrate dehydrogenase (metA), isocitrate dehydrogenase (metA), lipoate synthase (lipA), shikimate kinase I (aroK), L-tartrate dehydratase (ttdA). Glucose-1-phosphate uridylyltransferase (galU) is an enzyme associated with glycogenesis, and its downregulation by TPTC would inhibit synthesis of UDPglucose from glucose-1-phosphate and UTP (Thoden and Holden 2007). As a senescence-associated enzyme, downregulation of β-galactosidase (lacZ) might imply that E. coli is senescent after exposure to TPTC (Pardee et al. 1959). Transcriptional activities of these two genes were both downregulated more than 2.0-fold by TPTC. Expression of 3-phosphoserine phosphatase (serB) was upregulated by more than 2.0-fold, which indicates that a phosphoserine phosphatase process might be disturbed by exposure to TPTC (Veiga-da-Cunha et al. 2004). 3-Phosphoserine phosphatase has been shown to be a breast cancer marker molecule (Pestlin et al. 2005), and its altered expression might be indicative of another new toxicity mechanism by TPTC. The fact that nearly 18 % of all altered genes were classified as “regulatory proteins” suggested that TPTC can also cause toxicity through its disturbance of transcriptional regulators, activators, or inhibitors, especially for processes involving DNA. Four genes, cld, mcrA, rmf, and wrbA, were downregulated more than 2.0-fold. Based on downregulation of cld, the length of the O-antigen component of lipopolysaccharides would be disturbed after exposure of E. coli to TPTC (Raetz and Whitfield 2002). As a nuclease, downregulation of mcrA protein suggested the potential damage to DNA of bacteria after exposure of TPTC (Anton and Raleigh 2004). The fact that the ribosome modulation factor was shown to influence survival of E. coli under acid stress has already been shown by others (Yamagishi et al. 1993). Thus, downregulation of rmf could be indicative of damage to this bacterium. Disturbance of wrbA was proposed to be implicated in protection against oxidative stress (Burnett et al. 1974). Structural proteins, such as membrane proteins and water major intrinsic protein (MIP) channels, represented another Environ Sci Pollut Res (2013) 20:803–811 protein group altered by TPTC. aqpZ encodes for water MIP channels (Hovijitra et al. 2009), which was downregulated by less than 0.5-fold. aqpZ protein’s downregulation would disturb the cell’s osmoregulatory capacity since it allows E. coli to adapt to osmotic variations by rapid diffusion of water molecules. Otherwise, the fact that both skp and ompA were downregulated by TPTC demonstrated that skp can bind outer membrane proteins, such as ompA. Lack of skp protein would lead to accumulation of protein aggregates in the periplasm, which also implies that skp can recognize early folding intermediates of outer membrane proteins (Schafer et al. 1999). The gene mglB, which encodes for the D-galactose-binding periplasmic protein, was downregulated by less than 0.5-fold. Downregulation of expression of this protein would inhibit transport of galactose and glucose. TPTC elicited transcriptional alteration of a group of “rRNA or tRNA” genes, which produced RNA after expression. All genes in this category were downregulated by TPTC. rrnC, as one of seven ribosomal RNA operons (Yeon et al. 2008), was suppressed less than 0.2-fold. This suggested that inhibition of decoding mRNA into amino acids might be a mechanism of toxicity for TPTC. The gene menG, which is related to adenosylmethionine and belongs to the group of “amino acids formation,” was downregulated by TPTC. This suggested that inhibition of adenosylmethionine formation was another toxicity pathway of TPTC. TPTC altered transcription of a group of stress responsive genes, which can be divided into three categories according to previous studies (Onnis-Hayden et al. 2009): detoxification (uspB), drug resistance/sensitivity (evgA), and general stress (uspA). Both uspB and evgA are related to compound-/ chemical-induced mortality or stress, such as response to antibiotics, and were downregulated after exposure to TPTC. However, uspA was upregulated by TPTC, which implied that biochemical and biophysical homeostasis of the cell were disturbed after a 3-h exposure to TPTC. After construction of the correlation network, significant relationships among genes altered by TPTC were observed. Through the process of the network construction, a graphical Gaussian model, also known as covariance selection or concentration graph, was employed. Based on the constructed network, two genes, aroH and rrnC, seemed to have been very actively involved in the response to the exposure with TPTC and were related with six and four other genes, respectively. The gene aroH encodes 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS), which is feedbackregulated by tyrosine and phenylalanine (Shumilin et al. 2004) and is the primary target for metabolic regulation of aromatic biosynthesis by feedback inhibition in bacteria and fungi (Keith et al. 1991). Based on the observed significant correlations, it is hypothesized that disturbance of DAHPS would affect four genes including wrbA, cld, rmf, and glgs. Fold change of expression of rrnC was less than 0.2, and 809 downregulation of expression of this gene might contribute to or is affected by four related genes (uspF, aqpZ, galU, aroH) through the gene network. The results indicate that the E. coli whole cell array has the potential to identify novel biomarkers for determination of specific chemical classes in environmental media (Gou et al. 2010; Watson and Mutti 2004). Three general principles are proposed for selection of biomarkers of chemical pollution based on use of the E. coli array: (1) The endpoints need to be chemical-specific; (2) the magnitude of changes in gene expression should be related to the concentration of chemical; and (3) the change in gene expression should be great enough that it can be monitored easily. Based on these criteria, rrnC, cld, and glgS are recommended as potential biomarkers for TPTC, as their fold changes in expression were greater than 2 and proportional to concentrations of TPTC between 0.1 and 10 mg/L (Supplementary Figures 1A, 1B, 1C). cld and glgS genes encode proteins that regulate the length of the O-antigen component of lipopolysaccharide chains and can serve as a predictor of synthesis of glycogen. The gene rrnC directly encodes rRNA. However, to date, there were no reports that expression of these three genes is regulated by some specific chemicals. Suitability of these genes as biomarkers remains to be validated and requires further investigation into the consistency and TPTCspecificity of their responses. For this purpose, field TPTCsample tests will be performed with these genes in our future work. Acknowledgments The research was supported by grants from National Natural Science Foundation of China (NSFC) (grant no. 21007025), Jiangsu Provincial Key Technology R&D Program (#BE2011776), Jiangsu Provincial Environment Monitoring Station (Project # 1012), National Science and Technology Major Project (No. 2008ZX08526-003), and a Discovery Grant from the National Science and Engineering Research Council of Canada (Project # 326415-07), and a grant from the Western Economic Diversification Canada (Projects # 6578 and 6807). The authors wish to acknowledge the support of an instrumentation grant from the Canada Foundation for Infrastructure. Prof. Giesy was supported by the program of 2012 "High Level Foreign Experts" (#GDW20123200120) funded by the State Administration of Foreign Experts Affairs, P.R. China. He was also supported by the Canada Research Chair program, an at-large Chair Professorship at the Department of Biology and Chemistry and State Key Laboratory in Marine Pollution, City University of Hong Kong, and the Einstein Professor Program of the Chinese Academy of Sciences. Prof. Zhang was supported by a Program for New Century Excellence Talents in Universities (Ministry of Education, China). Mr. Guanyong Su was supported by the Shanghai Tongji Gao Tingyao Environmental Science and Technology Development Foundation (STGEF). References Anton BP, Raleigh EA (2004) Transposon-mediated linker insertion scanning mutagenesis of the Escherichia coli McrA endonuclease. 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Giesy1,2,,4,5, Hongxia Yu1,* 1 State Key Laboratory of Pollution Control and Resource Reuse & School of the Environment, Nanjing University, Nanjing, China 2 Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada 3 School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, S7N 5B3Canada 4 Department of Biomedical Veterinary Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada 5 Department of Biology and Chemistry and State Key Laboratory in Marine Pollution, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China Corresponding author: School of the Environment, Nanjing University, Nanjing, 210089, China Tel: 86-25-89680623 Fax: 86-25-83707304 E-mail: howard50003250@yahoo.com (Xiaowei Zhang) yuhx@nju.edu.cn (Hongxia Yu) Supporting Table 1: Description of Gene Function Groups Function Group Enzyme Regulatory Protein Structure Protein rRNA or tRNA Stress Responsive Pathway Amino Acids Formation Function Unclear Description Genes encoded enzymes, which played an important role in biochemical reaction. Genes produced protein after gene expression, which were transcriptional regulators, activators or inhibitors, especially for DNA process. Genes produced protein after gene expression, which were part of organism structure, for example, membrane protein, water MIP channel, Genes in the “RNA” group didn't produce protein but RNA, which might be rRNA or tRNA. Stress responsive genes. Genes were related to the formation of amino acids. Genes' functions were still not very clear right now. Supporting Table 2: Functions of 71 differentially expressed genes Type 1 pepE Protein function Classification (alpha)-aspartyl dipeptidase Enzyme 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase, tryptophan 2 aroH Protein Enzyme repressible 3 serB Protein 3-phosphoserine phosphatase Enzyme 4 add Protein adenosine deaminase Enzyme 5 gcvT Protein aminomethyltransferase Enzyme 6 lacZ Protein beta-galactosidase, lac operon Enzyme 7 cysK Protein cysteine synthase A,O-acetylserine sulfhydrolase A subunit Enzyme 8 serA Protein D-3-phosphoglycerate dehydrogenase Enzyme 9 dcd Protein Deoxycytidine triphosphate deaminase Enzyme 10 dmsA Protein dimethyl sulfoxide reductase, chain A Enzyme 11 ligB Protein DNA ligase Enzyme 12 fpr Protein ferredoxin-NADP reductase Enzyme 13 galU Protein glucose-1-phosphate uridylyltransferase Enzyme 14 gadB Protein glutamate decarboxylase B subunit Enzyme 15 metA Protein homoserine transsuccinylase Enzyme 16 icd Protein isocitrate dehydrogenase Enzyme 17 lipA Protein lipoate synthase Enzyme 18 cueO Protein multicopper oxidase with role in copper homeostasis Enzyme 19 aroK Protein shikimate kinase I Enzyme 20 ttdA Protein L-tartrate dehydratase Enzyme 21 cysB Protein Cys regulon transcriptional activator Regulatory Protein 22 cspD Protein DNA replication inhibitor Regulatory Protein DNA-binding membrane protein required for chromosome resolution and 23 ftsK Protein Regulatory Protein partitioning 24 gadX Protein DNA-binding transcriptional dual regulator Regulatory Protein 25 phoP Protein PhoP transcriptional regulator PhoP transcriptional dual regulator Regulatory Protein 26 mcrA Protein restriction of DNA at 5-methylcytosine residues Regulatory Protein 27 rmf Protein ribosome modulation factor Regulatory Protein 28 rsd Protein regulator of sigma D stationary phase protein, binds sigma 70 RNA Regulatory Protein polymerase subunit 29 wrbA Protein The purified WrbA protein has NAD(P)H:quinone oxidoreductase activity Regulatory Protein 30 fdhD 31 flgM Protein affects formate dehydrogenase-N Regulatory Protein Protein Negative regulator of flagellin synthesis Regulatory Protein 32 manX Protein PTS system mannose-specific EIIAB component Regulatory Protein 33 cld Protein regulator of length of O-antigen component of lipopolysaccharide chains Regulatory Protein 34 rpsT Protein 30S ribosomal subunit protein S20 Structure Protein 35 rpsU Protein 30S ribosomal subunit protein S21 Structure Protein 36 mglB Protein D-galactose-binding periplasmic protein Structure Protein 37 ytfF Protein inner membrane protein Structure Protein 38 b1403 Protein IS21 protein 2 Structure Protein 39 ompC Protein outer membrane porin protein C Structure Protein 40 ompA Protein outer membrane protein 3a (II*Gd) Structure Protein 41 skp Protein periplasmic molecular chaperone for outer membrane proteins Structure Protein 42 osmC Protein resistance protein, osmotically inducible Structure Protein 43 aqpZ Protein water MIP channel Structure Protein The 5S and 23S rRNAs are the RNA components of the large subunit (50S 44 rrnB rRNA subunit) of the E. coli ribosome.There are seven ribosomal RNA (rRNA) RNA operons, called rrnA, rrnB, rrnC, rrnD, rrnE, rrnG, and rrnH The 5S and 23S rRNAs are the RNA components of the large subunit (50S 45 rrnD rRNA subunit) of the E. coli ribosome.There are seven ribosomal RNA (rRNA) RNA operons, called rrnA, rrnB, rrnC, rrnD, rrnE, rrnG, and rrnH The 5S and 23S rRNAs are the RNA components of the large subunit (50S 46 rrnC rRNA subunit) of the E. coli ribosome.There are seven ribosomal RNA (rRNA) RNA operons, called rrnA, rrnB, rrnC, rrnD, rrnE, rrnG, and rrnH 47 argW tRNA 48 evgA Protein tRNA(argW) is one of seven arginine tRNAs RNA response regulator in two-component regulatory system with EvgS, Environmental involved in acid resistance, osmotic adaption, and drug resistance Stress Response Component of 49 uspB Protein ethanol tolerance protein Organism Environmental 50 uspA Protein universal stress global stress response regulator Stress Response S-adenosylmethionine: 2-demethylmenaquinone methyltransferase proteinE. Amino Acids 51 menG Protein The interaction of RraA with the degradosome is facilitated by protein-RNA Formation remodeling via the ATPase activity of RhlB 52 yfbV Protein conserved inner membrane protein Function Unclear 53 mntR Protein conserved protein Function Unclear 54 yhgF Protein conserved protein (3rd module) Function Unclear 55 yjdI Protein conserved protein;Uncharacterized protein yjdI Function Unclear 56 yhcG Protein function unknow Function Unclear 57 yafK Protein hypothetical protein Function Unclear 58 insA_7 Protein hypothetical protein Function Unclear 59 yaiE Protein hypothetical protein,UPF0345 family,function unknown Function Unclear 60 b3007 Protein unknown CDS Function Unclear 61 yhhY Protein predicted acetyltransferase Function Unclear 62 yeaU Protein predicted dehydrogenase D-malate dehydrogenase (decarboxylating) Function Unclear 63 glgS Protein predicted glycogen synthesis protein Function Unclear 64 proQ Protein predicted structural transport element Function Unclear 65 yedW Protein putative 2-component transcriptional regulator(yedV) Function Unclear 66 yedP Protein Putative mannosyl-3-phosphoglycerate phosphatase Function Unclear 67 ymcC Protein putative synthetase Function Unclear 68 yfiE Protein putative transcriptional regulator (LysR family) Function Unclear 69 uspF Protein putative universal stress protein F Function Unclear 70 yifE Protein Similar to Yersinia pestis KIM, hypothetical protein y0333 Function Unclear 71 ybcW Protein Uncharacterized protein Function Unclear Supporting Table 3: References of NOEC for different species exposure to TPTC Species Scientific Species Name Group Ankistrodesmus falcatus ssp. acicul (Wong et al. Concentration (Days) (ng/mL) EC50 8 2.0 4.0×10-1 EC50 NR 9.1×10-1 1.8×10-1 EC50 12 1.1×103 2.3×102 EC50 12 3.5×102 7.0×101 Fish LC50 2 6.4×101 1.4 1.4 Fish LOEC 110 2.3×10-1 9.3×10-2 9.3×10-2 Molluscs LC50 1 6.2×10-4 1.3×10-5 Moss or Fungi Scenedesmus Algae quadricauda Moss or (Fargasova 1997) Fungi Scenedesmus Algae quadricauda Moss or (Fargasova 2002) Fungi Scenedesmus Algae quadricauda Moss or (Fargasova 2002) Fungi (De Vries et al. 1991) Endpoint of NOEC (ng/mL)a Mean of (ng/mL) Algae 1982) Oryzias latipes Calculation Duration 4.0×10-1 1.0×102 Oncorhynchus mykiss (Nagase et al. 1991) Indoplanorbis exustus (Goel and Prasad 1978) 3.7 Indoplanorbis exustus (Goel and Molluscs LC50 1 3.5×102 7.4 Molluscs LC50 1 4.3×101 9.1×10-1 9.1×10-1 Worms LC50 4 2.4 5.1×10-2 5.1×10-2 Srivastava 1981) Lymnaea acuminate (Goel and Srivastava 1981) Tubifex tubifex (Fargasova 1997) a NOEC was calculated following “Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and their Uses”, which was drafted by U.S. Environmental Protection Agency. References: De Vries H, Penninks AH, Snoeij NJ, Seinen W (1991) COMPARATIVE TOXICITY OF ORGANOTIN COMPOUNDS TO RAINBOW TROUT ONCORHYNCHUS-MYKISS YOLK SAC FRY. Science of the Total Environment 103 (2-3):229-244 Fargasova A (1997) Comparative study of ecotoxicological effect of triorganotin compounds on various biological subjects. Ecotoxicology and Environmental Safety 36 (1):38-42 Fargasova A (2002) Structure-affected algicidal activity of triorganotin compounds. Bulletin of Environmental Contamination and Toxicology 69 (5):756-762. doi:10.1007/s00128-002-0125-3 Goel HC, Prasad R (1978) Action of Molluscicides on Freshly Laid Eggs of Snail Indoplanorbis-Exustus (Deshayes). Indian Journal of Experimental Biology 16 (5):620-622 Goel HC, Srivastava CP (1981) Laboratory evaluation of some molluscicides against french water snails, Indoplanorbis and Lymnaea species. J Commun Dis 13 (2):121-127 Nagase H, Hamasaki T, Sato T, Kito H, Yoshioka Y, Ose Y (1991) Structure-Activity-Relationships for Organotin Compounds on the Red Killifish Oryzias-Latipes. Applied Organometallic Chemistry 5 (2):91-97 Wong PTS, Chau YK, Kramar O, Bengert GA (1982) Structure-Toxicity Relationship of Tin-Compounds on Algae. Canadian Journal of Fisheries and Aquatic Sciences 39 (3):483-488 Supporting Table 4: Classification of differentially expressed genes and proportion of each groups basing on the function of genes (see in Supplementary Table 1) and fold change. Fold Change 1.5 - 2.0 2.0 - 3.0 3.0 - 4.0 7.0 - 8.0 Genes cysK, dcd, dmsA, gadB, fpr, gcvT, pepE, metA, serA, ttdA, icd, ligB, lipA, cueO, aroK, fdhD, flgM, ftsK, gadX, manX, rsd, phoP, cysB, cspD, ompA, ompC, osmC, ytfF, rpsT, rpsU, b1403, rrnB, rrnD, argW, uspA, uspB, evgA, yaiE, yeaU, yedP, yedW, yfbV, proQ, yfiE, yhgF, ymcC, b3007, yafK, mntR lacZ, serB, galU, aroH, add, wrbA, cld, rmf, mglB, skp, aqpZ, glgS, insA_7, uspF, yhcG, yhhY, yifE, yjdI mcrA, menG, ybcW rrnC Number 49 18 3 1 Each color represents one toxic pathway induced by TPTC, and detailed description of each toxic pathway can be found in Supplementary Table 1. О “enzyme”; О “Regulatory Protein”; О “Component of Organism”; О “rRNA or tRNA”; О “Environmental Stress Response”; О “Amino Acids Formation”; О “Function Unclear”. Supporting Figure 1: Gene expression profiles of three potential biomarkers.