Aerobic degradation and metabolite identification of the N-heterocyclic indole by the Pseudomonas putida strain mpky-1 isolated from subtropical mangrove sediment

Abstract

Aerobic biodegradation and metabolite identification of indole by the Pseudomonas putida strain mpky-1 isolated from coastal sediment of the Inner Deep Bay of Hong Kong was investigated in this study. This strain had 99.1% similarity with P. putida known. The biochemical degradation pathway of indole involved an initial hydroxylation reaction at the C-2 position to form oxindole followed by a second hydroxylation at the C-3 position to isatin prior to the cleavage of the 5-member carbon ring. This bacterium grew better at 22• C though it was capable of growth at low temperature (15• C in this study) with a longer lag phase. Both the bacterial specific growth rate and the biodegradation rate increased from 0.0035/hr to 0.0249/hr and from 15• C to 30• C, respectively. P. putida mpky-1 grew quicker at pH 6.4 (specific growth rate, 0.0115/hr) than pH 7.4 (specific growth rate, 0.0066/hr) and pH 8.4 (specific growth rate, 0.036/hr) although the lag time of bacterial growth at pH 7.4 and pH 8.4 (15.01 hr and 15.00 hr, respectively) was very similar. The decrease in bacterial growth rate was observed when salinity increased from 5‰ to 30‰. P. putida mpky-1 may adapt to the Mai Po and Inner Deep Bay and degrade indole due to the polluted condition. Keywords: aerobic degradation, indole, heterocyclic aromatics, metabolic pathway, Pseudomonas putida, environmental factors * Correspondence to: Ji-Dong Gu, School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China; Email: jdgu@hku.hk