The Megaplasmid pAO1 of Arthrobacter Nicotinovorans and Nicotine Catabolism. In: Schwartz E, editor. Microbial Megaplasmids. Berlin: Springer Berlin Heidelberg; 2009. pp. 271-82. [DOI: 10.1007/978-3-540-85467-8_12]

Genome-wide investigation of the genes involved in nicotine metabolism in Pseudomonas putida J5 by Tn5 transposon mutagenesis

Pseudomonas putida J5 is an efficient nicotine-degrading bacterial strain isolated from the tobacco rhizosphere. We successfully performed a comprehensive whole-genome analysis of nicotine metabolism-associated genes by Tn5 transposon mutagenesis in P. putida J5. A total of 18 mutants with unique insertions screened from 16,324 Tn5-transformants failed to use nicotine as the sole carbon source. Flanking sequences of the Tn5 transposon were cloned with a shotgun method from all of the nicotine-growth-deficient mutants. The potentially essential products of mutated gene were classified as follows: oxidoreductases, protein and metal transport systems, proteases and peptidases, transcriptional and translational regulators, and unknown proteins. Bioinformatic analysis of the Tn5 insertion sites indicated that the nicotine metabolic genes were separated and widely distributed in the genome. One of the mutants, M2022, was a Tn5 insert into a gene encoding a homolog of 6-hydroxy-L-nicotine oxidase, the second enzyme of nicotine metabolism in Arthrobacter nicotinovorans. Genetic and biochemical analysis confirmed that three open reading frames (ORFs) from an approximately 13-kb fragment recovered from the mutant M2022 were responsible for the transformation of nicotine to 3-succinoyl-pyridine via pseudooxynicotine and 3-succinoyl semialdehyde-pyridine, the first three steps of nicotine degradation. Further research on these mutants and the Tn5-inserted genes will help us characterize nicotine metabolic processes in P. putida J5.

Comparative genome analysis reveals the molecular basis of nicotine degradation and survival capacities of Arthrobacter

Arthrobacter is one of the most prevalent genera of nicotine-degrading bacteria; however, studies of nicotine degradation in Arthrobacter species remain at the plasmid level (plasmid pAO1). Here, we report the bioinformatic analysis of a nicotine-degrading Arthrobacter aurescens M2012083, and show that the moeB and mogA genes that are essential for nicotine degradation in Arthrobacter are absent from plasmid pAO1. Homologues of all the nicotine degradation-related genes of plasmid pAO1 were found to be located on a 68,622-bp DNA segment (nic segment-1) in the M2012083 genome, showing 98.1% nucleotide acid sequence identity to the 69,252-bp nic segment of plasmid pAO1. However, the rest sequence of plasmid pAO1 other than the nic segment shows no significant similarity to the genome sequence of strain M2012083. Taken together, our data suggest that the nicotine degradation-related genes of strain M2012083 are located on the chromosome or a plasmid other than pAO1. Based on the genomic sequence comparison of strain M2012083 and six other Arthrobacter strains, we have identified 17 σ(70) transcription factors reported to be involved in stress responses and 109 genes involved in environmental adaptability of strain M2012083. These results reveal the molecular basis of nicotine degradation and survival capacities of Arthrobacter species.

pAO1 of Arthrobacter nicotinovorans and the spread of catabolic traits by horizontal gene transfer in gram-positive soil bacteria

The 165-kb megaplasmid pAO1 of Arthrobacter nicotinovorans carries two large gene clusters, one involved in nicotine catabolism (nic-gene cluster) and one in carbohydrate utilization (ch-gene cluster). Here, we propose that both gene clusters were acquired by A. nicotinovorans by horizontal gene transfer mediated by pAO1. Protein-protein blast search showed that none of the published Arthrobacter genomes contains nic-genes, but Rhodococcus opacus carries on its chromosome a nic-gene cluster highly similar to that of pAO1. Analysis of the nic-genes in the two species suggested a recombination event between their nic-gene clusters. Apparently, there was a gene exchange between pAO1, or a precursor plasmid, and a nic-gene cluster of an as yet unidentified Arthrobacter specie or other soil bacterium, possibly related to Rhodococcus, leading to the transfer by pAO1 of this catabolic trait to A. nicotinovorans. Analysis of the pAO1 ch-gene cluster revealed a virtually identical counterpart on the chromosome of Arthrobacter phenanthrenivorans. Moreover, the sequence analysis of the genes flanking the ch-gene cluster suggested that it was acquired by pAO1 by Xer-related site directed recombination and transferred via the plasmid to A. nicotinovorans. The G+C content, the level of sequence identity, gene co-linearity of nic- and ch-gene clusters as well as the signs of recombination events clearly supports the notion of pAO1 and its precursor plasmids as vehicles in HGT among Gram + soil bacteria.

Genome sequence of a nicotine-degrading strain of Arthrobacter

We announce a 4.63-Mb genome assembly of an isolated bacterium that is the first sequenced nicotine-degrading Arthrobacter strain. Nicotine catabolism genes of the nicotine-degrading plasmid pAO1 were predicted, but plasmid function genes were not found. These results will help to better illustrate the molecular mechanism of nicotine degradation by Arthrobacter.

Nicotine degradation enhancement by Pseudomonas stutzeri ZCJ during aging process of tobacco leaves

Nicotine is a key harmful component of tobacco and cigarettes, and the development of low-nicotine cigarettes is of increasing importance in the market. The objectives of this study are to isolate native nicotine-degrading strains and evaluate their feasibility for nicotine reduction during the aging (or fermentation) of tobacco leaves. A novel nicotine-degrading strain was isolated and identified as Pseudomonas stutzeri ZCJ based on its 16S rDNA sequence and morphological-biochemical characteristics. In submerged cultures, P. stutzeri ZCJ could tolerate 4.5 g/L nicotine and completely degrade 1.5 g/L nicotine within 24 h at 37°C and pH 7.4. The addition of glucose (1 g/L) could improve nicotine degradation by P. stutzeri ZCJ in submerged cultures. After submerged culturing, the cell suspension of P. stutzeri ZCJ could be utilized to improve nicotine reduction in tobacco leaves during solid-state fermentation. The nicotine content of tobacco leaves decreased by as much as 32.24% after 7 days of solid-state fermentation by P. stutzeri ZCJ, suggesting the industrial application potential of the native strain to enhance nicotine degradation during the aging of tobacco leaves.