Some flow cytometers have the ability to physically separate different sub-populations of interest (cell sorting) depending on their cytometric characteristics (stream-in-air), thus permitting the recovery and purification of cell subsets from a mixed population for further applications (Bergquist et al., 2009; Davey, 2010). In natural samples in particular, a very important advantage of FCM is the opportunity to analyze micro-organisms with minimal pre-treatment and without the need for cultivation steps, also taking into account that the most of natural bacteria are resistant to cultivation (Fig. 2). Furthermore, FCM is particularly well-suited for the investigation of natural picoplankton. This is because of their small size (.
