LAUSR

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.