RIBOSOMAL RNA-BASED OLIGONUCLEOTIDE PROBES TO IDENTIFY MARINE GREEN ULTRAPHYTOPLANKTON

Oligonucleotide probes based on small subunit 18S rRNA variable region sequences, were designed and used to discriminate groups of marine gr een ultraphytoplankton of similar size and morphology. Hybridization o f probes was visualized using a combination of biotinylated oligonucle otides and fluorescein labeled avidin. Increased fluorescent signal wa s generated by building a complex of biotinylated probe, fluorescein l abeled avidin and biotinylated anti-avidin. Cells of one phylogenetic group were easily differentiated from morphologically similar cells of a different phylogenetic group. Design of specific probes allowed ide ntification of Mantoniella squamata, Micromonas pusilla, Pseudoscourfi eldia marina and the micromonadophyte clone CCMP 1194. This technique should be readily adaptable to open ocean samples and should greatly f acilitate the description and quantification of ultraphytoplankton in the open ocean.