The use of thermostable fluorescent proteins for live imaging in Sulfolobus acidocaldarius.

Introduction: Among hyperthermophilic organisms, in vivo protein localization is challenging due to the high growth temperatures that can disrupt proper folding and function of mostly mesophilic-derived fluorescent proteins. While protein localization in the thermophilic model archaeon S. acidocaldarius has been achieved using antibodies with fluorescent probes in fixed cells, the use of thermostable fluorescent proteins for live imaging in thermophilic archaea has so far been unsuccessful. Given the significance of live protein localization in the field of archaeal cell biology, we aimed to identify fluorescent proteins for use in S. acidocaldarius. Methods: We expressed various previously published and optimized thermostable fluorescent proteins along with fusion proteins of interest and analyzed the cells using flow cytometry and (thermo-) fluorescent microscopy. Results: Of the tested proteins, thermal green protein (TGP) exhibited the brightest fluorescence when expressed in Sulfolobus cells. By optimizing the linker between TGP and a protein of interest, we could additionally successfully fuse proteins with minimal loss of fluorescence. TGP-CdvB and TGP-PCNA1 fusions displayed localization patterns consistent with previous immunolocalization experiments. Discussion: These initial results in live protein localization in S. acidocaldarius at high temperatures, combined with recent advancements in thermomicroscopy, open new avenues in the field of archaeal cell biology. This progress finally enables localization experiments in thermophilic archaea, which have so far been limited to mesophilic organisms.

Sessile Lifestyle Offers Protection against Copper Stress in Saccharolobus solfataricus.

Some archaea from the genus Sulfolobus are important for bioleaching of copper, where metal resistant microorganisms are required. Biofilm generation is one of the ways microorganisms cope with some stimuli in nature, including heavy metals. The response to external factors, particularly in the biofilm form of life, is still underexplored in archaea. To explore how model thermoacidophilic archaeon Saccharolobus solfataricus faces copper stress during this lifestyle, changes in biofilms were studied using crystal violet staining, confocal fluorescence microscopy, and qPCR approaches. It was found that biofilm formation reached a maximum at 0.5 mM Cu, before starting to decrease at higher metal concentrations. The morphology of biofilms at 0.5 mM Cu was observed to be different, displaying lower thickness, different sugar patterns, and higher amounts of cells compared to standard growing conditions. Furthermore, copA, which is responsive to intracellular Cu concentration, was downregulated in biofilm cells when compared with planktonic cells exposed to the same metal concentration. The latest results suggests that cells in biofilms are less exposed to Cu than those in planktonic culture. In a PolyP-deficient strain, Cu was not able to induce biofilm formation at 0.5 mM. In summary, the findings reported here suggest that the biofilm form of life confers S. solfataricus advantages to face stress caused by Cu.Biofilm formation remains a relatively unexplored topic in archaeal research. Therefore, this knowledge in model organisms such as S. solfataricus, and how they use it to face stress, could be of great importance to engineer organisms with improved capabilities to be applied in biotechnological processes, such as bioleaching of metals.

Application of the endogenous CRISPR-Cas type I-D system for genetic engineering in the thermoacidophilic archaeon Sulfolobus acidocaldarius.

CRISPR (clustered regularly interspaced short palindromic repeats)-Cas systems are widely distributed among bacteria and archaea. In this study, we demonstrate the successful utilization of the type I-D CRISPR-Cas system for genetic engineering in the thermoacidophilic archaeon Sulfolobus acidocaldarius. Given its extreme growth conditions characterized by a temperature of 75°C and pH 3, an uracil auxotrophic selection system was previously established, providing a basis for our investigations. We developed a novel plasmid specifically designed for genome editing, which incorporates a mini-CRISPR array that can be induced using xylose, resulting in targeted DNA cleavage. Additionally, we integrated a gene encoding the ß-galactosidase of Saccharolobus solfataricus into the plasmid, enabling blue-white screening and facilitating the mutant screening process. Through the introduction of donor DNA containing genomic modifications into the plasmid, we successfully generated deletion mutants and point mutations in the genome of S. acidocaldarius. Exploiting the PAM (protospacer adjacent motif) dependence of type I systems, we experimentally confirmed the functionality of three different PAMs (CCA, GTA, and TCA) through a self-targeting assessment assay and the gene deletion of upsE. Our findings elucidate the application of the endogenous Type I-D CRISPR-Cas system for genetic engineering in S. acidocaldarius, thus expanding its genetic toolbox.

Methods for Markerless Gene Deletion and Plasmid-Based Expression in Sulfolobus acidocaldarius.

A well-functioning genetic system, which is important for studying gene functions in vivo, requires a transformation method, a vector system and a selection system. Sulfolobus acidocaldarius is a crenarchaeal model organism that grows optimally at 75 °C and a pH of 3. These extreme growth conditions cause some difficulties in developing a genetic system. With continuous efforts, versatile genetic tools have been developed for different species from the order of Sulfolobales. In this chapter, we describe the methods for the available genetic tools in S. acidocaldarius including a (1) transformation method, (2) pop in/pop out strategy to generate markerless deletion mutants and (3) a plasmid-based expression system.

Putative Nucleotide-Based Second Messengers in the Archaeal Model Organisms Haloferax volcanii and Sulfolobus acidocaldarius.

Research on nucleotide-based second messengers began in 1956 with the discovery of cyclic adenosine monophosphate (3',5'-cAMP) by Earl Wilbur Sutherland and his co-workers. Since then, a broad variety of different signaling molecules composed of nucleotides has been discovered. These molecules fulfill crucial tasks in the context of intracellular signal transduction. The vast majority of the currently available knowledge about nucleotide-based second messengers originates from model organisms belonging either to the domain of eukaryotes or to the domain of bacteria, while the archaeal domain is significantly underrepresented in the field of nucleotide-based second messenger research. For several well-stablished eukaryotic and/or bacterial nucleotide-based second messengers, it is currently not clear whether these signaling molecules are present in archaea. In order to shed some light on this issue, this study analyzed cell extracts of two major archaeal model organisms, the euryarchaeon Haloferax volcanii and the crenarchaeon Sulfolobus acidocaldarius, using a modern mass spectrometry method to detect a broad variety of currently known nucleotide-based second messengers. The nucleotides 3',5'-cAMP, cyclic guanosine monophosphate (3',5'-cGMP), 5'-phosphoadenylyl-3',5'-adenosine (5'-pApA), diadenosine tetraphosphate (Ap4A) as well as the 2',3'-cyclic isomers of all four RNA building blocks (2',3'-cNMPs) were present in both species. In addition, H. volcanii cell extracts also contain cyclic cytosine monophosphate (3',5'-cCMP), cyclic uridine monophosphate (3',5'-cUMP) and cyclic diadenosine monophosphate (3',5'-c-di-AMP). The widely distributed bacterial second messengers cyclic diguanosine monophosphate (3',5'-c-di-GMP) and guanosine (penta-)/tetraphosphate [(p)ppGpp] could not be detected. In summary, this study gives a comprehensive overview on the presence of a large set of currently established or putative nucleotide-based second messengers in an eury- and a crenarchaeal model organism.

The Role of Polyphosphate in Motility, Adhesion, and Biofilm Formation in Sulfolobales.

Polyphosphates (polyP) are polymers of orthophosphate residues linked by high-energy phosphoanhydride bonds that are important in all domains of life and function in many different processes, including biofilm development. To study the effect of polyP in archaeal biofilm formation, our previously described Sa. solfataricus polyP (-) strain and a new polyP (-) S. acidocaldarius strain generated in this report were used. These two strains lack the polymer due to the overexpression of their respective exopolyphosphatase gene (ppx). Both strains showed a reduction in biofilm formation, decreased motility on semi-solid plates and a diminished adherence to glass surfaces as seen by DAPI (4',6-diamidino-2-phenylindole) staining using fluorescence microscopy. Even though arlB (encoding the archaellum subunit) was highly upregulated in S. acidocardarius polyP (-), no archaellated cells were observed. These results suggest that polyP might be involved in the regulation of the expression of archaellum components and their assembly, possibly by affecting energy availability, phosphorylation or other phenomena. This is the first evidence indicating polyP affects biofilm formation and other related processes in archaea.

The biology of thermoacidophilic archaea from the order Sulfolobales.

Thermoacidophilic archaea belonging to the order Sulfolobales thrive in extreme biotopes, such as sulfuric hot springs and ore deposits. These microorganisms have been model systems for understanding life in extreme environments, as well as for probing the evolution of both molecular genetic processes and central metabolic pathways. Thermoacidophiles, such as the Sulfolobales, use typical microbial responses to persist in hot acid (e.g. motility, stress response, biofilm formation), albeit with some unusual twists. They also exhibit unique physiological features, including iron and sulfur chemolithoautotrophy, that differentiate them from much of the microbial world. Although first discovered >50 years ago, it was not until recently that genome sequence data and facile genetic tools have been developed for species in the Sulfolobales. These advances have not only opened up ways to further probe novel features of these microbes but also paved the way for their potential biotechnological applications. Discussed here are the nuances of the thermoacidophilic lifestyle of the Sulfolobales, including their evolutionary placement, cell biology, survival strategies, genetic tools, metabolic processes and physiological attributes together with how these characteristics make thermoacidophiles ideal platforms for specialized industrial processes.

Global effect of the lack of inorganic polyphosphate in the extremophilic archaeon Sulfolobus solfataricus: A proteomic approach.

Inorganic polyphosphates (polyP) are present in all living cells and several important functions have been described for them. They are involved in the response to stress conditions, such as nutrient depletion, oxidative stress and toxic metals amongst others. A recombinant strain of Sulfolobus solfataricus unable to accumulate polyP was designed by the overexpression of its endogenous ppx gene. The overall impact of the lack of polyP on this S. solfataricus polyP (-) strain was analyzed by using quantitative proteomics (isotope-coded protein label, ICPL). Stress-related proteins, such as peroxiredoxins and heat shock proteins, proteins involved in metabolism and several others were produced at higher levels in the ppx expression strain. The polyP deficient strain showed an increased copper sensitivity and an earlier transcriptional up-regulation of copA gene coding for the P-type copper-exporting ATPase. This implies a complementary function of both copper resistance systems. These results strongly suggests that the lack of polyP makes this hyperthermophilic archaeon more sensitive to toxic conditions, such as an exposure to metals or other harmful stimuli, emphasizing the importance of this inorganic phosphate polymers in the adaptations to live in the environmental conditions in which thermoacidophilic archaea thrive. SIGNIFICANCE: Inorganic polyphosphate (polyP) are ubiquitous molecules with many functions in living organisms. Few studies related to these polymers have been made in archaea. The construction of a polyP deficient recombinant strain of Sulfolobus solfataricus allowed the study of the global changes in the proteome of this thermoacidophilic archaeon in the absence of polyP compared with the wild type strain. The results obtained using quantitative proteomics suggest an important participation of polyP in the oxidative stress response of the cells and as having a possible metabolic role in the cell, as previously described in bacteria. The polyP deficient strain also showed an increased copper sensitivity and an earlier transcriptional up-regulation of copA, implying a complementary role of both copper resistance systems.