From an environmental sample to a long-lasting culture: the steps to better isolate and preserve cyanobacterial strains

Cyanobacterial blooms represent a health hazard worldwide due to their toxic potential. The CyanoSurvey project was set up to evaluate the risk associated with the presence of toxigenic cyanobacteria in Australian drinking water reservoirs. It mainly targeted members of the following genera: Dolichospermum, Sphaerospermopsis, Chrysosporum, Cylindrospermopsis and Microcystis. In 2010 and 2011, 64 samples were collected nationally and 196 isolates were purified using several culture media and a concentration technique. The strains obtained were then cryopreserved using three different cryoprotectants. The efficacy of each medium, the applicability of a pre-treatment to the sample and the various cryoprotective agents were compared for several isolates of cyanobacteria. This study highlighted that the ASM-1 medium, used routinely by many laboratories for the isolation and maintenance of cyanobacteria, had the lowest efficacy for the isolation of cyanobacteria from environmental samples. Moreover, the use of a range of media combined with a concentration technique can significantly improve the chances of isolating and purifying certain groups of cyanobacteria. The use of 5 % DMSO for cryopreservation was shown to be a preferable choice of cryopreservative for most strains tested.