Table 3.
Frequency of 16S rRNA genes sequences of ammonia-oxidizing bacteria in clone libraries constructed with DNA from the CsCl gradient fractionsa
| Length of incubation, labeling, CsCl gradient fraction | Frequencyb of sequences derived from starting material from: |
|||||
|---|---|---|---|---|---|---|
| Leutra South (100 μM NH4Cl) |
Ammerbach (1,000 μM NH4Cl) |
|||||
| 13°C | 20°C | 30°C | 13°C | 20°C | 30°C | |
| 3-Week incubation | ||||||
| NaH13CO3, heavy fraction | 6 (6/104) | NA | 17 (9/52) | 12 (13/108) | NA | 10 (5/52) |
| NaH13CO3, light fraction | 2 (1/52) | NA | 2 (1/52) | 6 (3/54) | NA | 4 (2/52) |
| 6-Week incubation | ||||||
| NaH13CO3, heavy fraction | 40 (21/52) | 12 (6/52) | 14 (7/52) | 10 (10/104) | 25 (13/52) | 12 (6/52) |
| Unlabeled control, heavy fraction | NAc (0/52) | 0 (0/52) | 0 (0/52) | 1 (2/156) | 6 (3/52) | 0 (0/52) |
a
See Fig. 1.
b
Values are percentages and, in parentheses, number of AOB-like sequences/total number of bacterial 16S rRNA gene clones screened. NA, not analyzed.
c
A clone library constructed from the light DNA fraction of the labeled treatments revealed no positive clones out of 52 clones tested.