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

The perchlorate (ClO4-)-respiring organism, strain perclace, can grow using nitrate (NO3-) as a terminal electron acceptor. In resting cell suspension s, NO3- grown cells reduced ClO4-, and ClO4- grown cells reduced NO3-. Acti vity assays showed that nitrate reductase (NR) activity was 1.31 mu mol min (-1) (mg protein)(-1) in ClO4- grown cells, and perchlorate reductase (PR) activity was 4.24 mu mol min(-1) (mg protein)(-1) in NO3- grown cells. PR a ctivity was detected within the periplasmic space, with activities as high as 14 mu mol 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 r eductases are present in strain perclace to reduce NO3- and ClO4-.