Perchlorate and nitrate reductase activity in the perchlorate-respiring bacterium perclace

The perchlorate (ClO₄^?)-respiring organism, strain perc1ace, can grow using nitrate (NO₃^?) as a terminal electron acceptor. In resting cell suspensions, NO₃^? grown cells reduced ClO₄^?, and ClO₄^? grown cells reduced NO₃^?. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min^?1 (mg protein)^?1 in ClO₄^? grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min^?1 (mg protein)^?1 in NO₃^? grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min^?1 (mg protein)^?1. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO₃^? and ClO₄^?.