Laxa isolated from Antarctica is a new source of the antifungal metabolite amphotericin B.

Background: The need for new antibiotic drugs increases as pathogenic microorganisms continue to develop resistance against current antibiotics. We obtained samples from Antarctica as part of a search for new antimicrobial metabolites derived from filamentous fungi. This terrestrial environment near the South Pole is hostile and extreme due to a sparsely populated food web, low temperatures, and insufficient liquid water availability. We hypothesize that this environment could cause the development of fungal defense or survival mechanisms not found elsewhere.

Results: We isolated a strain of Laxa from a soil sample obtained from an abandoned penguin's nest. Amphotericin B was the only metabolite secreted from Laxa with noticeable antimicrobial activity, with minimum inhibitory concentration of 0.125 μg/mL against . This is the first time that amphotericin B has been isolated from an organism other than the bacterium . In terms of amphotericin B production, cultures on solid medium proved to be a more reliable and favorable choice compared to liquid medium.

Conclusions: These results encourage further investigation of the many unexplored sampling sites characterized by extreme conditions, and confirm filamentous fungi as potential sources of metabolites with antimicrobial activity.