Some of these organisms have significant capacities to both heterotrophically nitrify and denitrify [2, 10, 19] and some synthesize [N.sub.2]O or [N.sub.2] during the course of heterotrophic nitrification [17, 20] or heterotrophic nitrification-aerobic denitrification metabolism [10,14-16,18, 21].
Identification of the bacterium as a Cupriavidus pauculus spurred an examination of its [Cu.sup.2+] and [Ni.sup.2+] resistance capacities, its ability to heterotrophically nitrify PO in the presence of these metals, and its use of the xenobiotic phenol in the absence or presence of [Cu.sup.2+] and [Ni.sup.2+] as this genus is known for its tolerance of metals and use of xenobiotics.
pauculus UM1 to produce nitrogenous gasses while heterotrophically nitrifying PO, the bacterium was grown to midto-late logarithmic phase in the PO-mineral salts medium described below, harvested by centrifugation (10,000 xg for 10 min) and washed twice in 50 mM pH 7.0 phosphate buffer to make resting cells.
pauculus UM1's ability to heterotrophically nitrify PO when either [Cu.sup.2+] or [Ni.sup.2+] was present, three different types of growth experiments were conducted.
To determine if the bacterium produces either [N.sub.2] or [N.sub.2]O while heterotrophically nitrifying, we attempted to grow the bacterium in sealed test tubes from which gasses could be sampled.
A number of organisms produce either [N.sub.2] or [N.sub.2]O while heterotrophically nitrifying or during heterotrophic nitrification-aerobic denitrification [2, 14, 16, 17, 20].
contains a nirS-like gene which it uses to denitrify , the organism did not invoke its use when heterotrophically nitrifying as evidenced by the lack of either [N.sub.2]O or [N.sub.2] synthesis under the heterotrophic nitrification or heterotrophic nitrificationaerobic denitrification conditions of the current study.
pauculus UM1 also grew readily and heterotrophically nitrified well, when in NB-PO with either 1mM [Cu.sup.2+] or 0.5 mM [Ni.sup.2+] (Table 1).
pauculus UM1 to heterotrophically nitrify PO in the absence of other carbon sources (no NB present) when either [Cu.sup.2+] or [Ni.sup.2+] was present was investigated.