Chemolithotrophic growth of the aerobic hyperthermophilic bacterium Thermocrinis ruber OC 14/7/2 on monothioarsenate and arsenite.

Novel insights are provided regarding aerobic chemolithotrophic growth of Thermocrinis ruber OC14/7/2 on the electron donors arsenite and monothioarsenate. Thermocrinis ruber is a hyperthermophilic bacterium that thrives in pH-neutral to alkaline hot springs and grows on hydrogen, elemental sulfur, and thiosulfate. Our study showed that T. ruber can also utilize arsenite as sole electron donor producing arsenate. Growth rates of 0.024 h(-1) were lower than for oxidation of thiosulfate to sulfate (µ = 0.247 h(-1)). Fast growth was observed on monothioarsenate (µ = 0.359 h(-1)), comprising different abiotic and biotic redox interactions. The initial dominant process was abiotic transformation of monothioarsenate to arsenate and elemental sulfur, followed by microbial oxidation of sulfur to sulfate. Elevated microbial activity during stationary growth of T. ruber might be explained by microbial oxidation of thiosulfate and arsenite, both also products of abiotic monothioarsenate transformation. However, the observed rapid decrease of monothioarsenate, exceeding concentrations in equilibrium with its products, also indicates direct microbial oxidation of arsenic-bond S(-II) to sulfate. Free sulfide was oxidized abiotically too fast to play a role as electron donor for T. ruber. Our present laboratory and previous field studies suggest that thioarsenates can either indirectly or directly be used by (hyper)thermophiles in arsenic-sulfidic environments.

Thioarsenate transformation by filamentous microbial mats thriving in an alkaline, sulfidic hot spring.

Thioarsenates dominate arsenic speciation in sulfidic geothermal waters, yet little is known about their fate in the environment. At Conch Spring, an alkaline hot spring in Yellowstone National Park, trithioarsenate transforms to arsenate under increasingly oxidizing conditions along the drainage channel, accompanied by an initial increase, then decrease of monothioarsenate and arsenite. On-site incubation tests were conducted using sterile-filtered water with and without addition of filamentous microbial mats from the drainage channel to distinguish the role of abiotic and biotic processes for arsenic species transformation. Abiotically, trithioarsenate was desulfidized to arsenate coupled to sulfide oxidation. Monothioarsenate, however, was inert. Biotic incubations proved that the intermediate accumulation of arsenite in the drainage channel is microbially catalyzed. In the presence of sulfide, microbially enhanced sulfide oxidation coupled to reduction of arsenate to arsenite could simply enhance abiotic desulfidation of trithioarsenate and potentially also monothioarsenate. However, we were also able to show, in sulfide-free medium, direct microbial transformation of monothioarsenate to arsenate. Some arsenite formed intermediately, which was subsequently also microbially oxidized to arsenate. This study is the first evidence for microbially mediated thioarsenate species transformation by (hyper)thermophilic prokaryotes.

Cisplatin sensitivity is related to late DNA damage processing and checkpoint control rather than to the early DNA damage response.

The present study aimed at elucidating mechanisms dictating cell death triggered by cisplatin-induced DNA damage. We show that CL-V5B hamster mutant cells, a derivative of V79B, are hypersensitive to cisplatin-induced apoptotic death. CL-V5B cells are characterized by attenuated cisplatin-induced early (2-6 h) stress response, such as phosphorylation of stress-activated protein kinases (SAPK/JNK), ATM and Rad3-related (ATR) protein kinase, histone H2AX and checkpoint kinase-1 (Chk-1). Human FANCC cells also showed a reduced phosphorylation of H2AX and SAPK/JNK at early time point after cisplatin treatment. This was not the case for BRCA2-defective VC-8 hamster cells, indicating that the FA core complex, rather than its downstream elements, is involved in early damage response. The alleviated early response of CL-V5B cells is not due to a general dysfunction in ATM/ATR-regulated signaling. It is rather due to a reduced formation of primary cisplatin-DNA adducts in the hypersensitive mutant as shown by analysis of DNA platination, DNA intra- and interstrand crosslink formation and DNA replication blockage. Despite of lower initial DNA damage and attenuated early DNA damage response (DDR), CL-V5B cells are characterized by an excessive G2/M arrest as well as an elevated frequency of DNA double-strand breaks (DSB) and chromosomal aberrations (CA) at late times (16-24h) after cisplatin exposure. This indicates that error-prone processing of cisplatin-induced lesions, notably interstrand crosslinks (ICL), and the formation of secondary DNA lesions (i.e. DSB), results in a powerful delayed DNA damage response and massive pro-apoptotic signaling in CL-V5B cells. The data provide an example that the initial level of cisplatin-DNA adducts and the corresponding early DNA damage response do not necessarily predict the outcome of cisplatin treatment. Rather, the accuracy of DNA damage processing and late checkpoint control mechanisms determine the extent of cell death triggered by cisplatin-induced DNA lesions.