Relationship between structures of substituted indolic compounds and their degradation by marine anaerobic microorganisms.
Degradation of selected indolic compounds including indole, 1-methylindole, 2-methylindole, and 3-methylindole was assessed under methanogenic and sulfate-reducing conditions using the serum-bottle anaerobic technique and marine sediment from Victoria Harbour, Hong Kong as an inoculum. Our results showed that indole degradation was achieved in 28 days by a methanogenic consortium and 35 days by a sulfate-reducing consortium. During degradation under both conditions, two intermediates were isolated, purified and identified as oxindole and isatin (indole-2,3-dione) suggesting that both methanogenic and sulfate-reducing bacteria use an identical degradation pathway. Degradation processes followed two steps of oxidation accomplished by hydroxylation and then dehydrogenation at 2- and then 3-position sequentially prior to the cleavage of the pyrrole ring between 2- and 3-positions. However, none of 1-methylindole or 2-methylindole was degraded under any conditions. 3-Methylindole (3-methyl-1H-indole, skatole) was transformed under methanogenic conditions and mineralized only under sulfate-reducing conditions. It is clear that methyl substitution on 1- or 2-position inhibits the initial attack by hydroxylation enzymes making them more persistent in the environment and posing longer toxic impact.
Gu
Ji-Dong
JD
Environmental and Molecular Microbiology, South China Sea Institute of Oceanography, Chinese Academy of Sciences, Guangzhou. jdgu@hkucc.hku.hk
Fan
Yanzhen
Y
Shi
Hanchang
H
D001421:Bacteria, Anaerobic / Q000502:physiology*; D001673:Biodegradation, Environmental; D007211:Indoles / Q000378:metabolism*; D008745:Methylation; D014874:Water Pollutants, Chemical / Q000378:metabolism*
D007211:Indoles; D014874:Water Pollutants, Chemical