Effect of cadmium on regulation of gene expression in bacteria

Cadmium (Cd) has no known biological function and is of concern as an environmental contaminant due to its extreme toxicity and ability to cause cell mutations and cancer. However, molecular mechanisms of Cd toxicity are still not completely clear. This prompted us to carry out a systemic study to understand how cadmium causes toxicity in cells.; Cadmium toxicity heavily depends on dose and bacterial species. A series of bacterial community were tested against a gradient concentration of cadmium. Of them, one is to measure the change of metabolic and structural diversity of a soil bacterial community in response to cadmium by using Biolog Ecoplate and DGGE based on PCR. A very low concentration of cadmium was tested to be able to cause several losses in function and species. 1ug/ml was selected for further experiment on gene expression.; To response to cadmium toxicity, bacteria would active a series of stress response to defense themselves. How cell response to cadmium globally remain to know. Based on study of above community response, 1ug/ml of cadmium was spiked to E.coli to investigate global response in mRNA level by employing oligo microarray and real-time RT-PCR. Cluster analysis was applied to profile genome-wide dynamic transcriptions and to analyze functional groups that manifested significant changes. The results showed there were a total of 1525 transcripts that underwent a 2 fold or greater change in expression, of which 674 showed a coefficient of variation >0.4. Among these, a broad range of stress response systems were induced by Cd, including the SOS, heat shock, oxidative stress, cold shock, osmotic shock, and systems for DNA repair, taxis, acid stress, Nudix, and zinc efflux. There were also several unknown functional proteins and intergenic regions that were upregulated by cadmium. Many of these responses correspond to energy conversation. The results further showed that several ribosomal protein (r-proteins) subunits (like L2, S15, and S6) and most zinc-binding proteins were induced, along with proteins that are associated with the typical UV-induced DNA repair system. In contrast, genes encoding DNA repair system associated with reactive oxygen species (ROS) were not significantly changed, suggesting that Cd toxicity is directly associated with significant changes in the expression of r-proteins/zinc-binding/cysteine-rich proteins rather than generation of ROS. Real time RT-PCR was carried out to confirm microarray data by quantifying 15 gene expression. The results showed that there was good agreement between the expression patterns for all 15 genes with an overall correlation coefficient of 0.87 for the RT-PCR and microarray data. Correlation coefficients for individual genes ranged between 0.596 and 1.000. Results of gene regulation patterns from this study may be valuable for future related carcinogenesis research.