TABLE 1.
Hydrogenase and urease activities of wild-type strain grown with different levels of nickel supplementationa
| Nickel concn (μM) | Mean activity ± SD
|
|
|---|---|---|
| Hydrogenase activity (nmol of H2 oxidized/ min/108 cells) | Urease activity (μmol of NH3/min/mg of protein) | |
| 0 | 0.4 ± 0.02 | 0.07 ± 0.01 |
| 1 | 0.8 ± 0.1 | 0.5 ± 0.03 |
| 2 | 1.5 ± 0.1 | 0.8 ± 0.08 |
| 6 | 1.7 ± 0.2 | 1.0 ± 0.08 |
| 8 | 2.0 ± 0.2 | 2.3 ± 0.1 |
| 10 | 2.6 ± 0.2 | 1.8 ± 0.2 |
| 20 | 1.8 ± 0.3 | 1.7 ± 0.1 |
a
All results are averages of five readings, and the experiment was repeated two additional times with similar results. According to the Students t test, the results for each nickel concentration are significantly greater than for the previous lower nickel concentration tested (P < 0.05), with the exception of the 10 μM versus 20 μM and the 2 μM versus 6 μM levels for hydrogenase and for the levels greater than 8 μM nickel for urease. For the hyaB mutant, there was no detectable activity even in the presence of externally added nickel; however, urease activities increased in a manner similar to that of the parent strain.