Detection of rRNA from OP3 LiM by fluorescence in situ hybridization. Archaea and OP3 LiM were detected in a methanogenic enrichment culture with probes ARCH-915 and OP3-565, respectively, in confocal laser scanning microscopy images: overlay (A) and individual signals of OP3 LiM rRNA (B, red), rRNA of Archaea (C, green), and DNA (D, blue, obtained by DAPI staining). Bars, 5 μm.