Uranium extremophily is an adaptive, rather than intrinsic, feature for extremely thermoacidophilic Metallosphaera species

Abstract

Thermoacidophilic archaea are found in heavy metal-rich environments, and, in some cases, these microorganisms are causative agents of metal mobilization through cellular processes related to their bioenergetics. Given the nature of their habitats, these microorganisms must deal with the potentially toxic effect of heavy metals. Here, we show that two thermoacidophilic Metallosphaera species with nearly identical (99.99%) genomes differed significantly in their sensitivity and reactivity to uranium (U). Metallosphaera prunae, isolated from a smoldering heap on a uranium mine in Thüringen, Germany, could be viewed as a "spontaneous mutant" of Metallosphaera sedula, an isolate from Pisciarelli Solfatara near Naples. Metallosphaera prunae tolerated triuranium octaoxide (U 3 O 8 ) and soluble uranium [U(VI)] to a much greater extent than M. sedula. Within 15 min following exposure to "U(VI) shock," M. sedula, and not M. prunae, exhibited transcriptomic features associated with severe stress response. Furthermore, within 15 min post-U(VI) shock, M. prunae, and not M. sedula, showed evidence of substantial degradation of cellular RNA, suggesting that transcriptional and translational processes were aborted as a dynamic mechanism for resisting U toxicity; by 60 min post-U(VI) shock, RNA integrity in M. prunae recovered, and known modes for heavy metal resistance were activated. In addition, M. sedula rapidly oxidized solid U 3 O 8 to soluble U(VI) for bioenergetic purposes, a chemolithoautotrophic feature not previously reported. M. prunae, however, did not solubilize solid U 3 O 8 to any significant extent, thereby not exacerbating U(VI) toxicity. These results point to uranium extremophily as an adaptive, rather than intrinsic, feature for Metallosphaera species, driven by environmental factors. uranium oxidation | uranium resistance | chemolithotrophy | terminal oxidases

Transcriptomes of the Extremely Thermoacidophilic Archaeon Metallosphaera sedula Exposed to Metal “Shock” Reveal Generic and Specific Metal Responses

“…However, their exact regulatory targets, transport substrates, and functions remain to be determined. When possible, ORFs for regulators, transporters, and hypothetical proteins are discussed here, but for a complete list, see Tables S1, S4, (6).…”

“…(iii) Response of M. sedula to uranium shock. UO 2 2ϩ challenge induced elements of phosphate and ammonium starvation, likely caused by the precipitation of ammonium and phosphate with uranyl ions, previously shown to occur as ammonium uranyl phosphate trihydrate (6). A homolog of the E. coli Ugp system (Msed_1181, Msed_1178) was upregulated in response to HD UO 2 2ϩ (see Table S6 in the supplemental material) (96).…”

“…Organic phosphate and carboxylic groups were responsible for the U(VI) complexation (27). Cellular dormancy, likely mediated by toxin-antitoxin loci, as a mechanism for uranium resistance was observed in the adaptive response of Metallosphaera prunae to U(VI) "shock" (6). M. prunae completely degraded rRNA, thus shutting down cellular metabolism and negating the toxic effects imposed by active growth during uranium challenge.…”

“…For some species within the Sulfolobales, metal oxidation mediated by membrane-bound, oxidase clusters provides a cellular bioenergetic benefit (3)(4)(5). However, at the same time, utilization of this energy source contributes to the toxicity of the biotope by mobilizing metal cations that can subsequently inhibit biological function (6,7). As a consequence, the interconnections between metal biooxidation, toxicity, and resistance are important to consider to have a full appreciation of how these unique microorganisms survive in extreme environments (8).…”

Transposon Mutagenesis Paired with Deep Sequencing of Caulobacter crescentus under Uranium Stress Reveals Genes Essential for Detoxification and Stress Tolerance

“…General and membrane stress responses were particularly pronounced when Shewanella oneidensis was exposed to U (18), and nucleic acid and protein damage have been shown to represent the primary modes of U toxicity in Desulfovibrio alaskensis G20 (19). Phosphate transporters and cell wall proteins are known to be important for survival following U exposure for the budding yeast Saccharomyces cerevisiae (20), whereas thermoacidophilic archaea employ temporary degradation of cellular RNA as a dynamic mechanism for resisting U toxicity (21). However, there is still a significant knowledge gap regarding the persistence of microbes in U-contaminated environments (9,22) as the mechanisms for responding to acute U toxicity are not necessarily the same as those that enable survival and growth over a longer term.…”