Improving Arsenic Tolerance of Pyrococcus furiosus by the Heterologous Expression of a Respiratory Arsenate Reductase.

Arsenate is a notorious toxicant that is known to disrupt multiple biochemical pathways. Many microorganisms have developed mechanisms to detoxify arsenate using the ArsC-type arsenate reductase and some even use arsenate as a terminal electron acceptor for respiration involving the arsenate respiratory reductase (Arr). ArsC-type reductases have been studied extensively but the phylogenetically-unrelated Arr system is less investigated and has not been characterized from Archaea. Herein, we heterologously-expressed the genes encoding Arr from the crenarchaeon Pyrobaculum aerophilum in the euryarchaeon Pyrococcus furiosus, both of which grow optimally near 100°C. Recombinant P. furiosus was grown on molybdenum (Mo)- or tungsten (W)- containing media and two types of recombinant Arr enzymes were purified, one containing Mo (Arr-Mo) and one containing W (Arr-W). Purified Arr-Mo had a 140-fold higher specific activity in arsenate (AsV) reduction than Arr-W and Arr-Mo also reduced arsenite (AsIII). The P. furiosus strain expressing Arr-Mo (the Arr strain) was able to use arsenate as a terminal electron acceptor during growth on peptides. In addition, the Arr strain had increased tolerance compared to the parent strain to arsenate and also, surprisingly, to arsenite. Compared to the parent, the Arr strain accumulated intracellularly almost an order of magnitude more arsenic when cells were grown in the presence of arsenite. XAS results suggest that the Arr strain of P. furiosus improves its tolerance to arsenite by increasing production of less toxic arsenate and non-toxic methylated arsenicals compared to the parent. [ABSTRACT FROM AUTHOR]