Biodegradation of 1-methylindole and 3-methylindole by mangrove sediment enrichment cultures and a pure culture of an isolated Pseudomonas aeruginosa Gs

Abstract

Indolic compounds are N-heterocyclic aromatic chemicals and have been detected at contaminated sites. Biodegradation of 1-methylindole (1MI) and 3-methylindole (3MI) was investigated initially using enrichment cultures with mangrove sediment obtained from Mai Po Nature Reserve of Hong Kong and subsequently with a pure culture of Pseudomonas aeruginosa Gs confirmed with 16S rRNA gene. At 2.0 mM, 1MI and 3MI were degraded in 4 and 3 days, respectively, by the respective 1MI- and 3MI-degrading enrichment cultures. When substrate concentrations were increased to 3.0,mM and 3.5,mM, slower degradation of 1MI and 3MI was observed indicating inhibitory effects from the substrates, possibly due to toxicity. In addition, no colony of bacteria could be observed on the agar plates amended with 3.5,mM 1MI or 4.0,mM 3MI, indicating that 1MI was more toxic than 3MI. Pseudomonas aeruginosa Gs, isolated from the enrichment culture, effectively utilized both substrates as the sole source of carbon and energy. Complete degradation of 1MI and 3MI was achieved after more than 40 days and 24 days, respectively, at an initial concentration of 2,mM in the culture. Effects of initial substrate concentration, pH and salinity on degradation of 1MI and 3MI by P. aeruginosa Gs were also studied in batch culture. The optimum pH and salinity for degrading both substrates by P. aeruginosa Gs was 7.0 and 5‰, respectively. Biodegradation kinetics of 1MI and 3MI by P. aeruginosa Gs could be described using a first-order kinetic model. Our results suggest that both 1MI and 3MI are biodegradable in the mangrove environment and that toxicity of 1MI could be a potential factor limiting the removal of the chemical in the environment by microorganisms. © Springer 2006.