The zone that surrounds microalgal cells is defined as phycosphere. Algae-bacteria interactions in the phycosphere can be neutral, positive or negative for algal growth and can vary depending on the main growth limiting factors. Besides, the same bacteria can either stimulate or inhibit algal growth. The identification of the bacterial species associated with microalgae and their influence on microalgal metabolism, is a key point. Tetraselmis suecica is a green marine microalga used in biotechnology, mainly as feed in aquaculture; moreover it is gaining importance for biofuel production. In this work, the bacterial community associated with cultures of T. suecica (strain F&M-M33) grown in different conditions (different seasons, conditions, and culture systems) were analyzed both by molecular and traditional techniques. A denaturing gradient electrophoresis gel (DGGE) approach was used to investigate the diversity of bacterial communities, analyzing three regions of 16S rDNA: bacterial diversity was better described using the V3-V4 region. Thanks to these results we performed an NGS metagenetic analysis. At the same time, 300 bacterial strains were isolated on Marine Agar medium, from T. suecica F&M-M33. The isolated bacteria were characterized for siderophore and indole-3-acetic acid production, to select strains able to actively stimulate microalgal growth