Assessment of Bacillus aerius and Bacillus toyonensis extracts as biocontrol agents against Biomphalaria alexandrina snails

Abstract

Schistosomiasis is one of the most deleterious parasitic diseases in the world and it is transmitted by aquatic snails. Consequently, there is a continuous need to search for new molluscicides to control the snails. The present study aimed to evaluate the molluscicidal activity of two bacterial diethyl ether extracts against adult Biomphalaria alexandrina snails. The present study indicated that LC50 and LC90 values were 193.734 and 280.670 mg/L for Bacillus aerius extract and 88.814 and 103.653 mg/L for Bacillus toyonensis extract against B. alexandrina snails after 48 h of exposure. After a 21-day chronic exposure period, the results showed that the sublethal concentrations (LCo and LC10) of both B. aerius and B. toyonensis extracts significantly decreased the survival rates of B. alexandrina snails. Likewise, the sublethal concentration (LC10) caused biochemical changes, including aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase enzymes, total protein, albumin, globulin, urea and creatinine and induced histopathological alterations in the digestive and hermaphrodite glands of exposed snails after 21 days. Despite negative effects on snails, we did not observe substantial morality in Artemia salina, a crustacean, after exposure to both extracts emphasizing that these extracts may be safe on other non-target aquatic organisms. Ultimately, our research suggests that B. aerius and B. toyonensis extracts can be used as promising biocontrol agents of B. alexandrina snails.