An essential role for tungsten in the ecology and evolution of a previously uncultivated lineage of anaerobic, thermophilic Archaea.

Trace metals have been an important ingredient for life throughout Earth's history. Here, we describe the genome-guided cultivation of a member of the elusive archaeal lineage Caldarchaeales (syn. Aigarchaeota), Wolframiiraptor gerlachensis, and its growth dependence on tungsten. A metagenome-assembled genome (MAG) of W. gerlachensis encodes putative tungsten membrane transport systems, as well as pathways for anaerobic oxidation of sugars probably mediated by tungsten-dependent ferredoxin oxidoreductases that are expressed during growth. Catalyzed reporter deposition-fluorescence in-situ hybridization (CARD-FISH) and nanoscale secondary ion mass spectrometry (nanoSIMS) show that W. gerlachensis preferentially assimilates xylose. Phylogenetic analyses of 78 high-quality Wolframiiraptoraceae MAGs from terrestrial and marine hydrothermal systems suggest that tungsten-associated enzymes were present in the last common ancestor of extant Wolframiiraptoraceae. Our observations imply a crucial role for tungsten-dependent metabolism in the origin and evolution of this lineage, and hint at a relic metabolic dependence on this trace metal in early anaerobic thermophiles.

Proteomic responses of oceanic Synechococcus WH8102 to phosphate and zinc scarcity and cadmium additions.

Synechococcus sp. WH 8102 is a motile marine cyanobacterium isolated originally from the Sargasso Sea. To test the response of this organism to cadmium (Cd), generally considered a toxin, cultures were grown in a matrix of high and low zinc (Zn) and phosphate (PO4 (3-)) and were then exposed to an addition of 4.4 pM free Cd(2+) at mid-log phase and harvested after 24 h. Whereas Zn and PO4 (3-) had little effect on overall growth rates, in the final 24 h of the experiment three growth effects were noticed: (i) low PO4 (3-) treatments showed increased growth rates relative to high PO4 (3-) treatments, (ii) the Zn/high PO4 (3-) treatment appeared to enter stationary phase, and (iii) Cd increased growth rates further in both the low PO4 (3-) and Zn treatments. Global proteomic analysis revealed that: (i) Zn appeared to be critical to the PO4 (3-) response in this organism, (ii) bacterial metallothionein (SmtA) appears correlated with PO4 (3-) stress-associated proteins, (iii) Cd has the greatest influence on the proteome at low PO4 (3-) and Zn, (iv) Zn buffered the effects of Cd, and (v) in the presence of both replete PO4 (3-) and added Cd the proteome showed little response to the presence of Zn. Similar trends in alkaline phosphate (ALP) and SmtA suggest the possibility of a Zn supply system to provide Zn to ALP that involves SmtA. In addition, proteome results were consistent with a previous transcriptome study of PO4 (3-) stress (with replete Zn) in this organism, including the greater relative abundance of ALP (PhoA), ABC phosphate binding protein (PstS) and other proteins. Yet with no Zn in this proteome experiment the PO4 (3-) response was quite different including the greater relative abundance of five hypothetical proteins with no increase in PhoA or PstS, suggesting that Zn nutritional levels are connected to the PO4 (3-) response in this cyanobacterium. Alternate ALP PhoX (Ca) was found to be a low abundance protein, suggesting that PhoA (Zn, Mg) may be more environmentally relevant than PhoX.