A novel bacterium involved in the degradation of 2-methylindole isolated from sediment of Inner Deep Bay of Hong Kong

Abstract

A bacterial strain, designated as MPKc, was isolated from the mudflat sediment of Mai Po Inner Deep Bay of Hong Kong Mai Po Nature Reserve by enrichment culturing with 2-methylindole as the sole source of carbon and energy. The microorganism was a Gram-negative, rod-shaped (0.4–0.6 μm × 1.0–2.2 μm) and aerobic bacterium. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain MPKc should be assigned as a novel bacterium, at least, at the species level. The 16S rDNA sequence most similiar to that of strain MPKc was Azoarcus evansii (94%) from available 16S rDNA sequences of the GenBank, indicating that strain MPKc was a member of the β-subclass of the Proteobacteria. Biochemical tests showed that strain MPKc was able to reduce nitrate to nitrogen. Carbon sources utilized by this strain included adipic acid, malate, citrate and phenylacetic acid although it only grew weakly on glucose, arabinose, mannose, mannitol, N-acetyl-glucosamine, maltose and gluconate. Strain MPKc showed no growth on capric acid. Its optimal growth occurred at 30°C, pH 6.5–7.5 and salinity 5–10‰. Strain MPKc was capable of degrading 80 μM 2-methylindole in 7 days under aerobic conditions. The possible chemical pathway for 2-methylindole degradation is through oxidation at 3-position or/and 2-position of the pyrrole ring.