Iem1i

cr1a2-110

cr1a2-31

Pseudomona Stutzen

Roseobacter denitrificans

Thauera aromatica 3cb3

Pseudomonas stutzen jm300

Azospirilium brasiliense

Pseudomonas aeruginosa Pseudomonas fluorescens Ralstonia eutropha

Thauera aromatica 3cb3

Azospirilium brasiliense

Pseudomonas stutzen jm300

Alcailigenes faecalis Pseudomonas stutzeri 14405

- Pseudomonas stutzeri jm300 Alcaligenes faecalis

- Pseudomonas stutzeri 14405

centrifugation. The diversity of this DNA can then be screened with a microarray, usually targeting the 16 S rRNA gene. By focusing only on DNA in which 13C is incorporated, a profile is obtained of a single functional guild, defined by the capacity to metabolize the substrate (DeLong 2001; Gray and Head 2001; Radajewski et al. 2003; Wellington et al. 2003).

Another promising, newly developed, technique goes under the name isotope array (Adamczyk et al. 2003). As in SIP, a labelled substrate is added to a community, but the label is a radioisotope such as 14C. rRNA is then extracted, labelled with a fluorescent label, and screened for 16 S rRNA diversity using a phylochip (see Section 4.2). By scanning for both flurorescence and radioactivity one can single out species from a designated functional guild that have proven to be active because they have taken up the substrate. Adamczyk et al. (2003) used this approach to profile nitrifying communities in activated sludge from two different wastewater-treatment plants. Diversity of ammonia-oxidizing bacteria in the sludge was assessed from the incorporation of added bicarbonate (leading to radioactively labelled rRNA) combined with hybridization to ammonia-oxidizing bacterium-specific 16 S rRNA probes (which is possible since ammonia-oxidizing bacteria constitute a monophyletic lineage). Such a combination of different molecular tools seems to be particularly promising.

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