Zamri Ishak

Use of intestinal Pseudomonas aeruginosa in fish to detect the environmental pollutant benzo[a]pyrene

This study examined the potential of Pseudomonas aeruginosa abundance in the intestines of fish as an indicator of exposure to benzo[a]pyrene (BaP). P. aeruginosa populations were enumerated in juvenile African catfish (Clarias gariepinus) injected intramuscularly three days previous with 0, 10, 30, 40, 50 or 70mg/kg of BaP. Hepatic EROD and GST activities and biliary fluorescent aromatic compounds (FACs) 1-OH BaP, 3-OH BaP, 7,8-D BaP and BaP were quantified to investigate agreements between the new indicator and established fish biomarkers. The shape of bacterial population (logarithm of colony-forming unit) dose-response curve generally matched those of biliary FACs concentrations. Conversely, the EROD and GST dose-response curves were generally the mirror images of the bacterial population curve. Changes in intestinal P. aeruginosa population appear to be an indirect effect of BaP exposure because exposure to 0-100μg/ml BaP had no effect on P. aeruginosa populations grown on agar plates containing BaP. Using intestinal P. aeruginosa population of fish as a universal indicator of BaP pollution in aquatic environments is discussed.Conversely, the EROD and GST dose-response curves were generally the mirror images of the bacterial population curve.

The effects of intramuscular and intraperitoneal injections of benzo[a]pyrene on selected biomarkers in Clarias gariepinus

This study investigated the dose-dependent and time-course effects of intramuscular (i.m.) and intraperitoneal (i.p.) injection of benzo[a]pyrene (BaP) on the biomarkers EROD activity, GST activity, concentrations of BaP metabolites in bile, and visceral fat deposits (Lipid Somatic Index, LSI) in African catfish (Clarias gariepinus). Intraperitoneal injection resulted in 4.5 times higher accumulation of total selected biliary FACs than i.m. injection. Hepatic GST activities were inhibited by BaP via both injection methods. Dose-response relationships between BaP injection and both biliary FAC concentrations and hepatic GST activities were linear in the i.p. injected group but nonlinear in the i.m. injected fish. Hepatic EROD activity and LSI were not significantly affected by BaP exposure by either injection route. We conclude that i.p. is a more effective route of exposure than i.m. for future ecotoxicological studies of PAH exposure in C. gariepinus.

Single-step and reagentless analysis of genetically modified soybean DNA with an electrochemical DNA biosensor

In many electrochemical DNA based biosensors, a redox indicator is required to be introduced separately to indicate the DNA hybridization event. In this work, we have developed a simple procedure for voltammetric determination of CaMV 35S gene modified DNA without the need for introduction of a redox indicator. The DNA biosensor contains an immobilized DNA probe and also a methylene blue redox indicator that is able to slow release during the hybridization event. The biosensor was constructed from a screen printed carbon paste electrode (SPE) coated with an acrylic microsphere (AM)–gold nanoparticle (AuNP) composite immobilized with single-stranded DNA probes, whilst methylene blue (MB) was immobilized in the hydrogel poly(2-hydroxyethyl methacrylate) membrane located next to the electrode. Genetically modified (GM) DNA was examined based on the reduction in the MB cathodic peak current (ipc) signal, which was ascribed to the DNA hybridization event, via the differential pulse voltammetry (DPV) method. The ipc current signal of MB after DNA hybridization with target CaMV 35S gene DNA was linearly related to the logarithmic target DNA concentration ranging from 2.0 × 10−12 to 2.0 × 10−7 M (R2 = 0.989) with a limit of detection (LOD) at 1.40 × 10−13 M. The proposed AM–AuNP composite DNA electrode gave satisfactory reproducibility performance with <10% (n = 5) relative standard deviation (RSD). The recoveries between 94.1 ± 2.2% and 103.7 ± 8.2% (n = 5) were obtained when the DNA biosensor was used for GM DNA determination in GM soybean DNA samples. The DNA biosensor based on the AM–AuNP composite deposited SPE and immobilized MB exhibited higher sensitivity by single-step analysis compared with conventional electrochemical sensors.