FIG. 2.

Combined MAR and FISH images of homogenized autotrophic nitrifying biofilms. Only nitrifying bacteria were successfully radiolabeled by incubation with [¹⁴C]bicarbonate for 6 h (A). Heterotrophic bacteria were all MAR negative under these incubation conditions (B). In situ hybridizations were performed with a combination of FITC-labeled Ntspa662 and TRITC-labeled Nso190 (red) (A) and with a combination of FITC-labeled mixed EUB338 probes (green) and TRITC-labeled Nso190 (red) (B). Bars = 10 μm. MAR++, strongly MAR positive; MAR−, MAR negative.