Rhomboids are conserved intramembrane serine proteases involved in cell signaling processes. Their role in prokaryotes is scarcely known and remains to be investigated in Archaea. We previously constructed a rhomboid homologue deletion mutant (ΔrhoII) in Haloferax volcanii, which showed reduced motility, increased novobiocin sensitivity, and an N- glycosylation defect. To address the impact of rhoII deletion on H. volcanii physiology, the proteomes of mutant and parental strains were compared by shotgun proteomics. A total of 1847 proteins were identified (45.8% of H. volcanii predicted proteome), from which 103 differed in amount. Additionally, the mutant strain evidenced 99 proteins with altered electrophoretic migration, which suggested differential post-translational processing/modification. Integral membrane proteins that evidenced variations in concentration, electrophoretic migration, or semitryptic cleavage in the mutant were considered as potential RhoII targets. These included a PrsW protease homologue (which was less stable in the mutant strain), a predicted halocyanin, and six integral membrane proteins potentially related to the mutant glycosylation (S-layer glycoprotein, Agl15) and cell adhesion/motility (flagellin1, HVO_1153, PilA1, and PibD) defects. This study investigated for the first time the impact of a rhomboid protease on the whole proteome of an organism.

Aims: To evaluate the ability of the haloarchaeon Haloferax volcanii to produce Ag and Au nanoparticles (NPs) and to characterize the obtained material in order to find relevant properties for future potential applications. Methods and Results: Nanoparticles were produced by incubating H. volcanii cells with the corresponding metal salt. In the presence of precursor salts, cultures evidenced a colour change associated to the formation of metallic nanostructures with plasmonic bands located in the visible range of the spectrum. X-ray fluorescence analysis confirmed the presence of Ag and Au in the NPs which were spherical, with average sizes of 25 nmol l À1 (Ag) and 10 nmol l À1 (Au), as determined by electronic microscopy. Fourier transformed infrared spectroscopy indicated that both types of NPs showed a stable protein capping. Ag NPs evidenced antibacterial activity and Au NPs improved the specificity of polymerase chain reaction reactions. Au and Ag NPs were able to reduce 4-nitrophenol when incubated with NaBH 4. Conclusions: Haloferax volcanii is able to synthesize metallic NPs with interesting properties for technological applications. Significance and Impact of the Study: Our data demonstrate the ability of H. volcanii to synthesize metal NPs and constitutes a solid starting point to deepen the study and explore novel applications.