Herbicide glyphosate efficiently inhibits growth of pathogenic <i>Prototheca</i> algae species, suggesting the presence of novel pathways for the development of anti-algal drugs

<i>Prototheca</i> are ubiquitous algae and occasional pathogens of humans and animals. While rare, the infection is often fatal and treatment options are limited to antifungals with low efficiency. Here, using growth curve assays, we demonstrate that five pathogenic species of <i>Prototheca</i> (<i>P. blaschkeae, P. wickerhamii, P. cutis, P. ciferrii, P. bovis</i>) were fully inhibited by 50-100 μg/mL of herbicide glyphosate, suggesting novel pathways that can be considered for anti-algal drug development.IMPORTANCE<i>Prototheca</i> are algae frequently found in the environment that occasionally cause infections in humans and animals. Although these infections are rare, they are often deadly for immunocompromised patients. Considering the rising ambient temperatures that promote algal bloom and a growing number of immunocompromised patients globally, such cases are likely to increase and will require efficient medications. Currently, the treatment is limited to antifungals that affect algal and animal membranes alike at concentrations close to toxic. Here, we hypothesized that targeting a pathway that is present in plants but not animals may be a new approach to the development of novel anti-algal compounds with high efficiency and lower toxicity. In this proof-of-principle study, we found that herbicide glyphosate, which targets the shikimate pathway found in plants but not in animals, efficiently inhibits all five tested pathogenic <i>Prototheca</i>, suggesting that the shikimate pathway may be a promising target for anti-algal drug development.