Biodegradation of quinoline by Nitrosomonas mobilis Ms1 through nitrification: A mechanistic study

Abstract

Effluents from pharmaceutical and coal gasification industries contain recalcitrant aromatic pollutants such as quinoline. Ammonia oxidizing bacteria (AOB) has been known to simultaneously oxidize ammonia and aromatic compounds. This study investigated the impact of quinoline, a nitrogen-containing heterocyclic aromatic compound, on nitrification by pure culture of AOB- Nitrosomonas mobilis Ms1. Quinoline has been found to inhibit nitrification to suspension culture by IC 50 value 40.01 μM. However, biofilm culture could withstand its inhibitory effect upto 50 μM. Morphological analysis of biofilm culture showed destruction in extracellularpolymeric substances (EPS) in the presence of quinoline at concentration of 1.5 mM and above. X-ray photoelectron spectroscopy (XPS) analysis of the biofilm surface showed loss of NH4+ peak in quinoline treated biofilm which indicated lower protein in EPS. Biodegradation analysis showed pyridine derivatives – 2,3-Pyridinedicarbonitrile, 2,4-Dicyanopyridine, and Pyridine, 2-[(3-methoxyphenyl) methyl] and hydroxylated aromatic such as 3-Hydroxy-4-methylbenzaldehyde and phenol, 4-[2-(methylamino) ethyl] as metabolic intermediates of quinoline degradation. These metabolic intermediates have been found to inhibit nitrification by blocking enzyme active site. Quinoline caused change in fatty acid methyl ester (FAME) profile which resulted in higher fraction of unsaturated FAME. This is one of the pioneer studies on quinoline biodegradation by a pure culture of AOB species, which could in turn aid to improve the efficacy of biological treatment of nitrogen-containing (heterocyclic compounds such as quinoline) wastewater.