Microcosms that were treated with oil but no nutrients (no N) or were treated with oil and a solution containing inorganic nutrients (1% N) and control microcosms that received nutrients only and no oil were sampled at zero time and 6 and 26 days after nutrient treatment (
27). DNA extracts were subjected to a nested PCR with primers specific for
Archaea. Archaea were detected in all microcosms immediately after oil addition and in all DNA extracts from the microcosm that was not treated with oil (
n = 15) (Table
1). However, exposure to oil had a negative effect on the ability to amplify archaeal 16S rRNA gene fragments.
Archaea were detected in only 1 of 12 samples taken on days 6 and 26 from the oil-treated microcosms. This reflected a real reduction in the archaeal community and not inhibition of PCR due to oil in the samples or bound to archaeal DNA. This was apparent because it was possible to amplify archaeal 16S rRNA gene fragments from zero-time samples which contained oil, as well as from the bioremediated microcosm on day 26, and bacterial 16S rRNA gene fragments could be readily amplified from the same DNA extracts (
27). Archaeal 16S rRNA genes have also readily been amplified from other oil-containing environments (
8,
37). DGGE profiling and subsequent cluster analysis of the DGGE data (based on the whole-track densitometric curves; Pearson correlation) revealed differences in archaeal community structure between the different microcosms at the start of the experiment (zero time) (Fig.
1, top). The archaeal communities of the bioremediated microcosms were clearly different from the communities in unfertilized, oil-treated microcosms and the control that was not treated with oil, clustering only at Pearson product-moment correlation coefficients (
r) of >0.61. Triplicate samples taken at the same time from a microcosm sometimes clustered differently when the whole-track densitometric curve information was taken into account (compare the 0%-N zero-time samples in Fig.
1, top, and the fertilizer-only day 26 samples in Fig.
1, bottom). However, when only the data for band presence or absence were compared, these triplicate samples clustered together (data not shown), showing that the differences were due to variation in the intensity of the bands rather than differences in the composition of the predominant
Archaea. For the microcosms that were not treated with oil no clear-cut changes in community structure over time were observed, both when clustering was based on the whole-track densitometric curve (Fig.
1, bottom) and when clustering was based on band positions only (data not shown). Despite the differences in clustering of the DGGE profiles, the most intense bands were found in all samples.