Methodology of protistan discovery: from rRNA detection to quality scanning electron microscope images

Each year, thousands of new protistan 18S rRNA sequences are detected in environmental samples. Many of these sequences are molecular signatures of new protistan species, classes, and/or kingdoms that have never been seen before. The main goal of this study was to enable visualization of these novel organisms and to conduct quality ultrastructural examination. We achieved this goal by modifying standard procedures for cell fixation, fluorescence in situ hybridization, and scanning electron microscopy (SEM) and by making these methodologies work in concert. As a result, the same individual cell can now be detected by 18S rRNA-targeted fluorochrome-labeled probes and then viewed by SEM to reveal its diagnostic morphological characteristics. The method was successfully tested on a wide range of protists (alveolates, stramenopiles, kinetoplastids, and cryptomonads). The new methodology thus opens a way for fine microscopy studies of many organisms previously known exclusively by their 18S rRNA sequences.