“…CO uptake at low concentrations by soils in particular contributes significantly to the global atmospheric CO budget [ 7 ]. In contrast, CO uptake attributed to Ni-dependent CO dehydrogenases has been reported for a phylogenetically more restricted group of Bacteria and Archaea, most of which are thermophilic [ 10 , 18 , 40 , 41 ]. The molecular biology, biochemistry, and physiology of selected isolates have been characterized extensively [ 9 , 10 , 15 , 18 , 42 ], but the ecological significance of Ni-COX remains largely unknown with a few exceptions.…”