Changes in the proteome of the cadmium-tolerant bacteria Cupriavidus taiwanensis KKU2500-3 in response to cadmium toxicity

Abstract

Cupriavidus taiwanensis KKU2500-3 is a cadmium (Cd)-tolerant bacterial strain that was previously isolated from rice fields contaminated with high levels of Cd. In 500 μmol/L CdCl2, the KKU2500-3 strain grew slower and with a more prolonged lag-phase than when grown in the absence of Cd. A proteomic approach was used to characterize the protein expression in the Cd-tolerant bacteria C. taiwanensis KKU2500-3 during growth under Cd stress. When compared with the untreated cells, a total of 982 differentially expressed protein spots were observed in the CdCl2-treated cells, and 59 and 10 spots exhibited >2- and >4-fold changes, respectively. The level of up- and downregulation varied from 2.01- to 11.26-fold and from 2.01- to 5.34-fold, respectively. Of the 33 differentially expressed protein spots analyzed by MALDI TOF MS/MS, 19 spots were successfully identified, many of which were involved in stress responses. The most highly upregulated protein (+7.95-fold) identified was the chaperone GroEL, which indicated that this factor likely contributed to the bacterial survival and growth in response to Cd toxicity. Detection of the downregulated protein flagellin (-3.52-fold) was consistent with the less effective ATP-mediated and flagella-driven motility. The flagella-losing cells were also observed in the Cd-treated bacteria when analyzed by scanning electron microscopy. Thus, the Cd-stressed cells may downregulate pathways involving ATP utilization in favor of other mechanisms in response to Cd toxicity. When the KKU2500-3 strain was grown in the presence of Cd, H2S was not detected, suggesting a possible role of the sulfur in precipitation with Cd. Apart from a general response, no specific process could be determined using the present proteomic approach. However, the potential role of protein folding-mediated GroEL, flagella-mediated motility and CdS biotransformation in Cd toxicity response observed in this study as well as the extent of Cd-tolerant mechanisms using other methods could facilitate the future application of this strain in addressing Cd environmental contamination.