Vitality and genetic fidelity of white-rot fungi mycelia following different methods of preservation

Basidiomycetes present specific problems with regard to their preservation, because most of them do not form resistant propagules in culture but exist only as mycelium. Usually these fungi can only be preserved by serial transfer on agar (labour-intensive procedures that can increase the danger of variation or loss of physiological or morphological features), or cryopreserved in liquid nitrogen (expensive). Cryopreservation at −80 °C and lyophilisation could be good alternatives.

In this work we set up and tested six protocols of cryopreservation at −80 °C, and 12 protocols of lyophilisation on 15 isolates of white-rot fungi (WRF) belonging to 10 species. The tested protocols were mainly characterized by the use of different growth media, protectants, time and number of perfusion with protectants and finally by the typology and origin of the samples to be cryopreserved (mycelium/agar plug, whole colony) or to lyophilise (mycelium/agar plug, mycelium fragment, whole colony). Cryopreservation and lyophilisation outcomes were checked, at morphological (macro- and microscopic features), physiological (growth rate and laccase, Mn-independent and Mn-dependent peroxidases activities) and genetic level (Amplified Fragment Length Polymorphisms analysis – AFLP). Vitality of all fungi was successfully preserved by all cryopreservation protocols at −80 °C, and by two lyophilisation methods. Our results showed that cryopreservation at −80 °C did not produce morphological changes in any isolate, while two isolates were affected by lyophilisation. None of the physiological features were lost, even though growth rate and enzyme activities were somehow influenced by all preservation methods. AFLP analysis showed that only the two isolates that varied in their morphology after lyophilisation produced a different DNA fingerprint pattern in comparison with that obtained before lyophilisation. These findings provide evidence that cryopreservation at −80 °C and lyophilisation are suitable alternatives to liquid nitrogen cryopreservation for preservation of some WRF strains.