Endophytic fungus Alternaria macrospora: A promising and eco-friendly source for controlling Aedes aegypti and its toxicity assessment on non-targeted organism, zebrafish (Danio rerio) embryos

Abstract

Fungal compounds are believed to be the most efficient method of addressing challenges with pesticide resistance and contamination of the environment. The present study was aimed to evaluate the larvicidal, pupicidal, ovicidal, histopathology profile, antibacterial, cytotoxic effects of cervical cancerous cells and its toxicity assessments using zebrafish embryo (Danio rerio). The isolates were confirmed by macroscopic, microscopic and PCR using a universal internal transcribed spacer primer for the molecular identification of the isolated fungus at the species level (GenBank - MN049541). The isolated fungus was first tested for its ability to produce toxic compounds in Aedes aegpti larvae in the 1–4th instar. For each instar of determined mosquito larvae, the secondary metabolites were evaluated in different bioassays at different test concentrations (100–500 μg/mL). The lethal concentrations of A. macrospora mycelial ethyl acetate extract that kill 50% of exposed larvae (LC50) and 90% of exposed larvae (LC90) were found in the first, second, third, and fourth instar larvae of A. aegypti (LC50 = 96.167, 131.370, 217.595, and 143.864 μg/mL and (LC90 = 395.16, 483.692, 882.545, and 655.722 μg/mL). After 120 h of exposure, the ovicidal bioassay's mean (%) was observed. A dose-dependent pattern was found in the enzymatic level of acetylcholinesterase in 4th instar larvae exposed to fungal mycelial metabolites. The treatment of 500 μg/mL of mycelia metabolites produced significant histopathological damage in the 4th instar mosquito larvae. The highest growth inhibition zones were observed during the antibacterial investigation of Alternaria macrospora metabolites against E. coli (22 mm) and S. aureus (20 mm). Also, the detected mycelium metabolites were tested for docking studies to identify their binding ability towards the E. coli FimH and S. aureus tyrosyl-RNA synthetase protein. The mycelium metabolites with different concentrations were further tested in the in-vivo zebrafish model to evaluate developmental toxicity. This is the first report on mosquito larvicidal and pupicidal activity of ethyl acetate metabolites produced by A. macrospora species. The study findings demonstrate that A. macrospora metabolites might be an ideal, cheap, small, and environmentally suitable source for controlling A. aegypti larvae.