How to cope with heavy metal ions: Insights into cellular and molecular stress response in Halobacterium salinarum R1 planktonic cells and biofilms

Halobacterium salinarum R1 is an extremely halophilic archaeon capable of adhesion and biofilm formation. We have recently shown that living in biofilms facilitates higher cell survival under heavy metal ion stress in this species, while specific rearrangements of the biofilm architecture were observed upon Ni2+ and Cu2+ exposition, respectively. In this study, quantitative analyses were performed by SWATH-LC-MS/MS to determine the respective proteomes under the influences of Ni2+ and Cu2+ in planktonic and biofilm cells. Quantitative data for 1180 proteins were gained, corresponding to 46% of the predicted proteome. In planktonic cells, 234 proteins showed significant abundance changes after metal ion treatment, of which 47% occurred combined in Cu2+ and Ni2+ treated samples. Regarding biofilms, significant changes were detected for 52 proteins. Only three proteins changed under both conditions, suggesting metal-specific stress responses in biofilms.