Breaking the paradigm- algae occur only sporadically in soils under a temperate climate.

are unicellular, achlorophyllous, yeast-like microalgae that have been implicated as the causative agents of opportunistic infections in animals and humans, collectively referred to as protothecosis. Still, the algae are typically saprophytic in nature and mostly occur in areas of high humidity and high organic matter content. Only a few recent studies have explored the environmental reservoir of . This work is the first study since the early 1980s to investigate the prevalence of spp. in natural terrestrial sources. A total of 226 soil samples were collected, with only 10 yielding growth. The overall isolation rate of the algae was 4.4%, with the predominant species being . These results show that algae only sporadically occur in soils of the temperate climatic zone. Consequently, this work contradicts the ubiquity of in soils, breaking the paradigm that, despite the lack of serious experimental appraisal, has long been perpetuated in the literature.IMPORTANCEThere is a scarcity of studies exploring the environmental habitat of , a rare and poorly studied genus of microalgae, comprising opportunistic pathogens of humans and animals. This work focuses on the occurrence of algae in soil environments. Given the potential hazard to human and animal health from exposure to environmental pathogens such as , the prevalence of the microalgae in soils deserves an insightful examination. The study is the first since the 1980s to assess the prevalence of spp. in natural terrestrial sources and the first ever performed to approach this topic by molecular methods. Soils have been considered to be ubiquitously inhabited by . This view has been perpetuated in the literature despite the lack of any serious experimental appraisal. Surprisingly, we found that the algae are very rare soil inhabitants, clearly breaking the prevailing paradigm of their ubiquity in this environment.