Molecular Stress Responses to Nano-Sized Zero-Valent Iron (nZVI) Particles in the Soil Bacterium Pseudomonas stutzeri

Abstract

Nanotoxicological studies were performed in vitro using the common soil bacterium Pseudomonas stutzeri to assess the potentially toxic impact of commercial nano-sized zero-valent iron (nZVI) particles, which are currently used for environmental remediation projects. The phenotypic response of P. stutzeri to nZVI toxicity includes an initial insult to the cell wall, as evidenced by TEM micrographs. Transcriptional analyses using genes of particular relevance in cellular activity revealed that no significant changes occurred among the relative expression ratios of narG, nirS, pykA or gyrA following nZVI exposure; however, a significant increase in katB expression was indicative of nZVI-induced oxidative stress in P. stutzeri. A proteomic approach identified two major defence mechanisms that occurred in response to nZVI exposure: a downregulation of membrane proteins and an upregulation of proteins involved in reducing intracellular oxidative stress. These biomarkers served as early indicators of nZVI response in this soil bacterium, and may provide relevant information for environmental hazard assessment.

A comparative study with biologically and chemically synthesized nZVI: applications in Cr (VI) removal and ecotoxicity assessment using indigenous microorganisms from chromium-contaminated site

“…A significant (p<0.05) decrease in the cell viability at 24 h was observed in both individual isolates and consortium when compared with control, whereas, an increase was observed in case of consortium when compared with individual treated bacterial isolates as reported in our previous reports (Jang et al 2014;Kumari et al 2014;Saccà et al 2014). However, the BS-nZVI treated consortium, and all five individual isolates showed an increase in the cell viability compared to CS-nZVI interacted samples.…”

Three Functional Biomarkers for Monitoring the Nanoscale Zero-Valent Iron (nZVI)-Induced Molecular Signature on Soil Organisms

“…1d) detected using the primers designed in this study is in accordance with previous findings using a proteomic approach, where superoxide dismutase protein was significantly upregulated (ratio +2.12) after treatment with nZVI (Saccà et al 2014a). Gramnegative soil bacteria showed a high transcriptional activity for the sodB biomarker upon exposure to nZVI for 14 and 21 days (Fig.…”

“…Previous in vitro studies carried out in our lab using a proteomic approach demonstrated that several proteins were differentially expressed as a consequence of bacterial culture exposure to nZVI Saccà et al 2013;Saccà et al 2014a). The main classes of the proteins upregulated were reported to be stressresponsive ones, including superoxide dismutase (SodB), thioredoxin (Trx) and tryptophanase (Trpase).…”

“…Table 2 shows the primer sequences used in this study. Quantification of the katB gene expression level in the soil samples was performed using the primer set previously described by Fajardo et al (2013) and Saccà et al (2014a). The tnaA gene was amplified using the primers previously described by Bernasconi et al (2007).…”

“…Transcriptional analyses showed that the katB gene (encoding catalase, a key component of the cellular detoxification pathway) (Saccà et al 2014ab) could be considered important marker for addressing the bacterial molecular stress response to nZVI. Moreover, proteomic assays Saccà et al 2014a) showed that after nZVI exposure, bacteria modulated the expression ratio of some proteins, particularly those involved in the reduction of the oxidant cellular environment caused by nZVI-induced reactive oxygen species (ROS). Hence, an upregulation of thioredoxin (Trx) and superoxide dismutase (SodB) proteins, both related to the cellular defence system against oxidative stress, was observed.…”