Is axenicity crucial to cryopreserve microalgae?

Area of Science:

• Phycology
• Microbiology
• Cryobiology

Background:

• Microalgal cultures, like those in the Coimbra Collection of Algae (ACOI), are often non-axenic, containing symbiotic bacteria.
• These bacterial partners can influence algal nutrient uptake but may hinder cryopreservation success by recovering faster than algae.
• Understanding these interactions is crucial for improving cryopreservation protocols for microalgal collections.

Purpose of the Study:

• To investigate the impact of associated organisms on the cryopreservation success of mucilaginous microalgae.
• To identify cell features influencing cryopreservation outcomes.
• To evaluate the effect of different cryoprotectants on partner organism proliferation during cryopreservation.

Main Methods:

• Selection of mucilaginous microalgae from the ACOI collection.
• Recording of cell features relevant to cryopreservation.
• Application of two-step cryopreservation tests using methanol (MeOH) or dimethyl sulfoxide (Me2SO).
• Assessment of microalgal viability and partner organism proliferation post-thaw.

Main Results:

• Cryopreservation success was higher in small, unicellular algae lacking outer structures.
• Intracellular vacuoles negatively impacted cryopreservation outcomes.
• Methanol (MeOH) cryoprotection induced partner organism proliferation, while dimethyl sulfoxide (Me2SO) mitigated this effect.
• Approximately half of the cells were recovered on average after cryopreservation.

Conclusions:

• Cellular morphology, particularly the absence of outer structures and vacuoles, significantly affects microalgal cryopreservation success.
• The choice of cryoprotectant is critical; Me2SO is preferable to MeOH for minimizing partner organism growth during cryopreservation.
• Further understanding of cultured consortia dynamics is essential for optimizing microalgal cryopreservation and research.