Association of heterotrophic bacteria with aggregated <i>Arthrospira platensis</i> exopolysaccharides: implications in the induction of axenic cultures

Inducing an axenic culture of the edible cyanobacterium <i>Arthrospira</i> (<i>Spirulina</i>) <i>platensis</i> using differential filtration alone is never successful; thus, it has been thought that, in non-axenic cultures, a portion of contaminating bacteria is strongly associated with <i>Arthrospira</i> cells. However, examination of the behavior of these bacteria during filtration revealed that they were not associated with <i>Arthrospira</i> cells but with aggregates of exopolysaccharides present in the medium away from the <i>Arthrospira</i> cells. Based on this finding, a rapid and reliable method for preparing axenic trichomes of <i>A. platensis</i> was established. After verifying the axenicity of the resulting trichomes on enriched agar plates, they were individually transferred to fresh sterile medium using a handmade tool, a microtrowel, to produce axenic cultures. With this technique, axenic cultures of various <i>A. platensis</i> strains were successfully produced. The technique described in this study is potentially applicable to a wider range of filamentous cyanobacteria.