Abstract
Microbial degradation of nicotine is an important process to control nicotine residues in the aqueous environment. In this study, a high active nicotine degradation strain named Pseudomonas sp. JY-Q was isolated from tobacco waste extract (TWE). This strain could completely degrade 5.0 g l−1 nicotine in 24 h under optimal culture conditions, and it showed some tolerance even at higher concentrations (10.0 g l−1) of nicotine. The complete genome of JY-Q was sequenced to understand the mechanism by which JY-Q could degrade nicotine and tolerate such high nicotine concentrations. Comparative genomic analysis indicated that JY-Q degrades nicotine through putative novel mechanisms. Two candidate gene cluster duplications located separately at distant loci were predicted to be responsible for nicotine degradation. These two nicotine (Nic) degradation-related loci (AA098_21325—AA098_21340, AA098_03885—AA098_03900) exhibit nearly completely consistent gene organization and component synteny. The nicotinic acid (NA) degradation gene cluster (AA098_17770–AA098_17790) and Nic-like clusters were both predicted to be flanked by mobile genetic elements (MGE). Furthermore, we analyzed the regions of genomic plasticity (RGP) in the JY-Q strain and found a dynamic genome carrying a type VI secretion system (T6SS) that promotes nicotine metabolism and tolerance based on transcriptomics and used in silico methods to identify the T6SS effector protein. Thus, a novel nicotine degradation mechanism was elucidated for Pseudomonas sp. JY-Q, suggesting its potential application in the bioremediation of nicotine-contaminated environments, such as TWEs.
Highlights
Nicotine is regarded as toxicant that can cause a variety of adverse environmental effects and preventable diseases
The JY-Q strain was incubated in 250 ml flasks with 100 ml sterilized basic salt medium (BSM) containing 2.0 g l−1 nicotine at 180 rpm and 30◦C
Nicotine tolerance of the JY-Q strain was evaluated at initial nicotine concentrations ranging from 1.0 to 10.0 g l−1 under defined optimal cultivation temperature and pH (Figure 1)
Summary
Nicotine is regarded as toxicant that can cause a variety of adverse environmental effects and preventable diseases. Nicotine biodegradation pathways have been characterized in several microorganisms, including, Pseudomonas (Tang et al, 2012) and Arthrobacter species (Baitsch et al, 2001). A pyrrolidine pathway of nicotine degradation was determined to be present in Pseudomonas This pathway involves nicotine oxidoreductase (NicA), pseudooxynicotine amidase (Pnao), 3-succinoylsemialdehyde-pyridne dehydrogenase (Sapd), 3-succinoylpyridine monooxygenase (SpmABC), 6-hydroxy-3succinoylpyridine hydroxylase (HspB), 2,5-dihydroxypyridine dioxygenase (Hpo), N-formylmaleamate deformylase (Nfo), maleamate amidohydrolase, or amidase (Ami), and maleate cis/transisomerase (Iso) (Tang et al, 2013). Multi-dimensional approaches are required to decipher either additional novel routes or entire nicotine degradation routes in incompletely known bacteria
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