Cultivation and application of nicotine-degrading bacteria and environmental functioning in tobacco planting soil

Nicotine, a toxic and addictive alkaloid from tobacco, is an environmental pollutant. However, nicotine-degrading bacteria (NDB) and their function in tobacco planting soil are not fully understood. First, 52 NDB strains belonging to seven genera were isolated from tobacco soil. The most dominant genera were Flavobacterium (36.5%), Pseudomonas (30.8%), and Arthrobacter (15.4%), and Chitinophaga and Flavobacterium have not been previously reported. Then, two efficient NDB strains, Arthrobacter nitrophenolicus ND6 and Stenotrophomonas geniculata ND16, were screened and inoculated in the compost fertilizer from tobacco waste. The nicotine concentrations were reduced from 1.5 mg/g (DW) to below the safety threshold of 0.5 mg/g. Furthermore, strain ND6 followed the pyridine pathway of nicotine degradation, but the degrading pathway in strain ND16 could not be determined according to genomic analysis and color change. Finally, the abundance of nicotine-degrading genes in tobacco rhizosphere soil was investigated via metagenomic analysis. Five key genes, ndhA, nctB, kdhL, nboR, and dhponh, represent the whole process of nicotine degradation, and their abundance positively correlated with soil nicotine concentrations (p < 0.05). In conclusion, various NDB including unknown species live in tobacco soil and degrade nicotine efficiently. Some key nicotine-degrading genes could be used in monitoring nicotine degradation in the environment. The fermentation of compost from tobacco waste is a promising application of efficient NDB.