Abstract
BackgroundNicotine-degrading microorganisms (NDMs) have recently received much attention since they can consume nicotine as carbon and nitrogen source for growth. In our previous work, we isolated an efficient nicotine-degrading fungus Aspergillus oryzae 112822 and first proposed a novel demethylation pathway of nicotine degradation in fungi. However, the underlying mechanisms of the demethylation pathway remain unresolved. In the present study, we performed a comparative transcriptome analysis to elucidate the molecular mechanisms of nicotine tolerance and degradation in A. oryzae 112822.ResultsWe acquired a global view of the transcriptional regulation of A. oryzae 112822 exposed to nicotine and identified 4381 differentially expressed genes (DEGs) by nicotine treatment. Candidate genes encoding cytochrome P450 monooxygenases (CYPs), FAD-containing amine oxidase, molybdenum cofactor (Moco)-containing hydroxylase, and NADH-dependent and FAD-containing hydroxylase were proposed to participate in the demethylation pathway of nicotine degradation. Analysis of these data also revealed that increased energy was invested to drive nicotine detoxification. Nicotine treatment led to overproduction of reactive oxygen species (ROS), which formed intracellular oxidative stress that could induce the expression of several antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxiredoxin (Prx). Thioredoxin system was induced to restore the intracellular redox homeostasis. Several glutathione S-transferases (GSTs) were induced, most likely to participate in phase II detoxification of nicotine by catalyzing the conjugation of glutathione (GSH) to active metabolites. The toxin efflux pumps, such as the ATP-Binding Cassette (ABC) transporters and the major facilitator superfamily (MFS) transporters, were overexpressed to overcome the intracellular toxin accumulation. By contrast, the metabolic pathways related to cellular growth and reproduction, such as ribosome biogenesis and DNA replication, were inhibited by nicotine treatment.ConclusionThese results revealed that complex regulation networks, involving detoxification, transport, and oxidative stress response accompanied by increased energy investment, were developed for nicotine tolerance and degradation in A. oryzae 112822. This work provided the first insight into the metabolic regulation of nicotine degradation and laid the foundation for further revealing the molecular mechanisms of the nicotine demethylation pathway in filamentous fungi.
Highlights
Nicotine-degrading microorganisms (NDMs) have recently received much attention since they can consume nicotine as carbon and nitrogen source for growth
This work revealed that complex regulation networks, involving detoxification, transport, and oxidative stress response accompanied by increased energy investment, were developed for nicotine tolerance and degradation in A. oryzae 112822
Nicotine degradation pathways in bacteria are represented by the pyridine pathway of A. nicotinovorans, the pyrrolidine pathway of P. putidia S16, and the Variant of pyridine and pyrrolidine (VPP) pathway of Ochrobactrum sp
Summary
Nicotine-degrading microorganisms (NDMs) have recently received much attention since they can consume nicotine as carbon and nitrogen source for growth. Several NDMs have been used to detoxify the tobacco wastes [9, 10], to reduce nicotine dependence of smokers with gradually reduced nicotine content in cigarettes [11], and to produce valuable pyridine derivatives for drug synthesis [12]. Among these NDMs, several bacteria, such as Arthrobacter nicotinovorans [13], Pseudomonas putida S16 [14], Pseudomonas sp. The enzymes involved in the first two pathways have been elucidated in detail [13, 14, 20,21,22,23,24,25,26], and several isoenzymes involved in the VPP pathway have been reported [17, 27]
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