FISH methods in phycology: Phototrophic biofilm and phytoplankton applications

Many photosynthetic microorganisms, living attached to immersed substrates or free in the water column, lack distinct morphological details, are small in size and often unculturable. Thus, whole-cell fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes has become a valuable and widely used technique to identify bacteria and protists within their natural communities. FISH methods not only allow direct, cultivation independent determination of community composition, but provide spatio-temporal quantification of microorganisms in the environment. Coupling of FISH techniques to Confocal Laser Scanning Microscopy (CLSM) has become essential for the assessment of diversity and structural integrity in three-dimensional complex biofilm samples. Combining FISH with microautoradiography (FISH-MAR) and microsensors also opens new perspectives in microbial ecology by providing new tools for revealing physiological properties of organisms with single-cell resolution. This paper briefly summarizes the application of FISH methods to phototrophic biofilm and phytoplankton research. The potential of DNA microarray technology in phycological research is highlighted, especially for the fast and accurate identification of HAB (Harmful Algal Bloom) species in marine phytoplankton. Some CLSM and FISH data from phototrophic biofilms from an Italian wastewater treatment plant are shown.