β-Galactosidase activity derived from a <i>norC–lacZ</i> fusion present in <i>B. japonicum</i> wild type (2499), <i>regR</i> (2499RR) or <i>regS</i> (2499RS) mutant cells.

<p>Cells were cultured under anoxic conditions or under 2% initial O₂ in Bergersen minimal medium without (BS) or with nitrate (BSN). Data are means with standard error (in parenthesis) from at least three independent cultures, assayed in triplicate. nd, not determined.