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Inducible promoters are one of the most important technical tools for cellular and molecular biology. The ability to deplete, replete, and overexpress genes on demand is the foundation of most functional studies. Here, we develop and characterize a new xylose-responsive promoter (Pxyl), the second inducible promoter system for the model haloarcheonHaloferax volcanii. Generating RNAseq datasets from cultures in the presence of four historically used inducers (arabinose, xylose, maltose, and IPTG), we mapped upregulated genomic regions largely repressed in the absence of the above inducers. The most upregulated promoter was found to control the expression of thexacEA(HVO_B0027-28) operon in the pHV3 chromosome. To characterize this promoter region, we cloned msfGFP (monomeric superfold green fluorescent protein) under the control of two different 5’ UTR fragments into a modified pTA962 vector: the first 250 bp (P250) and the whole 750 bp intergenic region (P750). The P250 region showed to express msfGFP constitutively and its expression does not respond to the presence or absence of xylose. However, the P750 promoter showed not only to be repressed in the absence of xylose but also expressed higher levels of msfGFP in the presence of the inducer. Finally, we validated our new inducible Pxyl promoter by reproducing morphological phenotypes already described in the literature. By overexpressing the tubulin-like FtsZ1 or FtsZ2, we observed similar, but slightly more pronounced morphological defects compared to the tryptophan-inducible promoter PtnaA. FtsZ1 overexpression created larger, deformed cells, whereas cells overexpressing FtsZ2 were smaller but mostly retained their shape. In summary, this work contributes with a new xylose-inducible promoter Pxyl that can be used simultaneously with the well-established PtnaA in functional studies inH. volcanii.

Coimmunoprecipitation is a powerful and commonly used method to identify protein-protein interactions in a physiological context. Here, we report a coimmunoprecipitation protocol that was adapted and optimized for the haloarchaeon Haloferax volcanii to identify interacting partners to the LonB protease. This protocol includes the in vivo cross-linking of H. volcanii proteins using two different crosslinker agents, dithiobis(succinimidyl propionate) and formaldehyde, followed by immunoprecipitation with anti-LonB antibody conjugated to Protein A - Sepharose beads. Tryptic on-bead protein digestion was performed combined with Mass Spectrometry analysis of peptides for the identification and quantification of LonB ligands.

The cellular protein repertoire is highly dynamic and responsive to internal or external stimuli. Its changes are largely the consequence of the combination of protein synthesis and degradation, referred collectively as protein turnover. Different proteomics techniques have been developed to determine the whole proteome turnover of a cell, but very few have been applied to archaea. In this chapter we describe a heavy isotope multilabeling method that allowed the successful analysis of relative protein synthesis and degradation rates on the proteome scale of the halophilic archaeon Haloferax volcanii. This method combines 15N and 13C isotope metabolic labeling with high-resolution mass spectrometry and data analysis tools (QuPE web-based platform) and could be applied to different archaea. © 2022. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.

Carotenoids are bioactive molecules known to promote human health. Many extreme halophilic archaea synthesize carotenoids, mainly represented by C

Phytoene synthase (PSY) converts two molecules of geranyl-geranyl diphosphate to phytoene, the key regulatory step in carotenogenesis. However, post-translational mechanisms that control PSY expression are scarcely understood. Carotenoid biosynthesis (mainly bacterioruberin) is a distinctive feature of haloarchaea thriving in hypersaline environments. Carotenogenesis is negatively regulated by the AAA+ LonB protease in the haloarchaeon Haloferax volcanii as it controls PSY degradation. We investigated the relevance of the C-terminal portion of HvPSY as a regulatory element for carotenoid biosynthesis. H. volcanii mutants were constructed to express full-length HvPSY protein (strain HVPSYwt) and truncated HvPSY lacking 10 (HVPSY10), 20 (HVPSY20) or 34 amino acids (HVPSY34) at the C-terminus. Cells of HVPSY20 and HVPSY34 showed hyperpigmentation (bacterioruberin content 3-fold higher than HVPSYwt) which correlated with increased PSY protein abundance (2-fold in HVPSY34) while they contained less psy transcript level compared with HVPSYwt. In vivo degradation assays showed that HvPSY34 was more stable than HvPSYwt. Collectively, these results show that the C-terminal region of HvPSY contains a ‘recognition determinant’ for proteolysis in H. volcanii. Preliminary evidence suggests that LonB is involved in the recognition mechanism. This study provides the first identification of a regulatory sequence in an archaeal PSY for the post-translational control of carotenogenesis.