Insights on Anabaena sp. PCC 7120 Responses to HCH Isomers: Tolerance, Degradation, and Dynamics on Potential lin...

Hexachlorocyclohexane (HCH) was extensively used as a pesticide until the 1990s. It was synthesized by benzene photochlorination, resulting in a mixture of stereoisomers, which included α-, β-, γ-, and δ-HCH, among others. It was later discovered that only the γ-HCH isomer (also called lindane) had insecticidal properties, so it began to be purified from this mixture, while the remaining HCH isomers (representing around 85%-90% of industrial HCH production) were disposed of in dumpsites, generating environmental issues. Several works have studied microbial-driven biodegradation and physiological responses to γ-HCH, but information concerning the other isomers is scarce. Since previous research showed that the cyanobacterium Anabaena sp. PCC 7120 is effective at removing lindane; this study focused on its responses to the α-, β-, and δ-HCH isomers. The results showed that Anabaena tolerates α- and γ-HCH well, with little impact on growth, while β- and δ-HCH are more poorly tolerated and negatively affect growth and cell physiology. It was also found that, in the presence of Anabaena sp. PCC 7120, both α- and γ-HCH are completely eliminated from supernatants while β- and δ-HCH are partially eliminated. Additionally, the linC gene was found to be expressed at twice the normal level in the presence of α- and γ-HCH at 2 mg/mL. Overall, this study reveals how Anabaena responds to key HCH isomers found in contaminated sites and supports its potential use in bioremediation.