Methylation deficiency of chromatin proteins is a non-mutational and epigenetic-like trait in evolved lines of the archaeon Sulfolobus solfataricus.

Archaea are a distinct and deeply rooted lineage that harbor eukaryotic-like mechanisms, including several that manage chromosome function. In previous work, the thermoacidophilic crenarchaeon, Sulfolobus solfataricus, was subjected to adaptive laboratory evolution to produce three strains, called SARC, with a new heritable trait of super acid resistance. These strains acquired heritable conserved transcriptomes, yet one strain contained no mutations. Homologous recombination without allele replacement at SARC acid resistance genes caused changes in both phenotype and expression of the targeted gene. As recombination displaces chromatin proteins, their involvement was predicted in the SARC trait. Native chromatin proteins are basic and highly abundant and undergo post-translational modification through lysine monomethylation. In this work, their modification states were investigated. In all SARC lines, two chromatin proteins, Cren7 and Sso7d, were consistently undermethylated, whereas other chromatin proteins were unaltered. This pattern was heritable in the absence of selection and independent of transient exposure to acid stress. The bulk of Sso7d was undermethylated at three contiguous N-terminal lysine residues but not at central or C-terminal regions. The N-terminal region formed a solvent-exposed patch located on the opposite side of the binding domain associated with the DNA minor groove. By analogy to eukaryotic histones, this patch could interact with other chromosomal proteins and be modulated by differential post-translational modification. Previous work established an epigenetic-like mechanism of adaptation and inheritance in S. solfataricus The identification of heritable epigenetic marks in this work further supports the occurrence of an epigenetic process in archaea.

Secretion and fusion of biogeochemically active archaeal membrane vesicles.

Microbes belonging to the genus Metallosphaera oxidize sulfidic minerals. These organisms thrive at temperature extremes and are members of the archaeal phylum Crenarchaeota. Because they can employ a lithoautotrophic metabolism, energy availability likely limits their activity raising questions about how they conduct biogeochemical activity. Vesicles are membrane encapsulated structures produced by all biological lineages but using very different mechanisms. Across the Crenarchaeota, it has been proposed that a eukaryotic-like Endosomal Sorting Complex Required for Transport system promotes formation of these structures but in response to unknown signals and for undefined purposes. To address such questions, Metallosphaera sedula vesicle formation and function were studied under lithoautotrophic conditions. Energy deprivation was evaluated and found to stimulate vesicle synthesis while energy excess repressed vesicle formation. Purified vesicles adhered rapidly to the primary copper ore, chalcopyrite, and formed compact monolayers. These vesicle monolayers catalyzed iron oxidation and solubilization of mineralized copper in a time-dependent process. As these activities were membrane associated, their potential transfer by vesicle fusion to M. sedula cells was examined. Fluorophore-loaded vesicles rapidly transferred fluorescence under environmentally relevant conditions. Vesicles from a related archaeal species were also capable of fusion; however, this process was species-specific as vesicles from different species were incapable of fusion. In addition, vesicles produced by a copper-resistant M. sedula cell line transferred copper extrusion capacity along with improved viability over mutant M. sedula cells lacking copper transport proteins. Membrane vesicles may therefore play a role in modulating energy-related traits in geochemical environments by fusion-mediated protein delivery.