Tips and tricks for high quality MAR-FISH preparations: focus on bacterioplankton analysis

The combination of microautoradiography and fluorescence in situ hybridization (MAR-FISH) is a powerful technique for tracking the incorporation of radiolabelled compounds by specific bacterial populations at a single cell resolution. It has been widely applied in aquatic microbial ecology as a tool to unveil key ecophysiological features, shedding light on relevant ecological issues such as bacterial biomass production, the role of different bacterioplankton groups in the global carbon and sulphur cycle, and, at the same time, providing insights into the life styles and niche differentiation of cosmopolitan members of the aquatic microbial communities. Despite its great potential, its application has remained restricted to a few laboratories around the world, in part due to its reputation as a "difficult technique". Therefore, the objective of this minireview is to highlight the impact of MAR-FISH application on aquatic microbial ecology, and also to provide basic concepts, as well as practical tips, for processing MAR-FISH preparations, thus aiming to contribute to a more widespread application of this powerful method.