The pros and cons of axenic cultures in cyanobacterial research

An ongoing issue among cyanobacteriologists is the sometimes-mandatory obligation of working with axenic cultures. Proponents of axenicity argue that it is the safest way to determine the true producer of a particular compound, as a contaminant-free pure culture possesses only the targeted strain's genetic material. For biotechnological applications, axenicity allows the produced biomass to be used in valuable and high-end purposes, such as pharmaceutics, agriculture, cosmetic and food sectors. Nevertheless, axenic cultures are expensive and hard to obtain, requiring constant surveillance. Some strains are described as recalcitrant to axenicity, dying off or ceasing the biosynthesis of some compounds. Axenic culturing greatly deviates from natural conditions, which may alter gene expression and fail to embody ecological relationships. In non-axenic cultures, a complex interaction network among microorganisms exists, with shared metabolic pathways generating biochemical diversity that allows strains to survive stress and laboratory conditions. On the other hand, a non-axenic condition may limit the final use of the biomass produced, as unknown contaminants might be present. Additionally, depending on the ecological interaction established, competition between different microorganisms can negatively influence the growth of the targeted population. This review discusses axenicity in cyanobacterial research and the feasibility of performing high-quality scientific research without axenic cultures, presenting both culturing approaches and shedding light on the intricate nature of microbial interactions.