Isomerization of non-insecticidal α-hexachlorocyclohexane (HCH)to insecticidal γ-HCH by Pseudomonasstrain Ptm

<p align="justify">Pseudomonas strain Ptm+ grew on α-hexa-
chlorocyclohexane (HCH, CAS no. 319846), using it as
the sole source of carbon and energy. In a replacement-
culture study, with the non-insecticidal α-HCH, γ-HCH
(CAS no. 58899) was the first metabolite noticed at 6 h,
and transient accumulation of insecticidal γ-HCH oc-
curred for up to 18 h. Although delta- (CAS no. 319868)
and beta-isomers (CAS no. 319857) were also detected,
their concentrations were very low. By 18 h of incuba-
tion, about 23% of the α-HCH added was transformed
into the gamma-isomer. Subsequently, the concentration
of γ-HCH in the medium fell. Thin-layer chromatogra-
phy, gas chromatography, gas chromatography-mass
spectrometry and mosquito-larval bioassay analyses
confirmed the formation of γ-HCH. This was associated
with the formation of three more metabolites.</p>