No abstract

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. Graphical Abstract

Bacterial strain H33T was isolated from tobacco plant soil and was characterized using a polyphasic taxonomy approach. Strain H33T was a Gram-stain-negative, rod-shaped, non-motile and strictly aerobic bacterium. Phylogenetic analyses based on 16S rRNA gene sequences and coding sequences of the up-to-date bacterial core gene set (92 protein clusters) indicated that H33T belongs to the genus Sphingobium . Strain H33T showed the highest 16S rRNA gene sequence similarity to Sphingobium xanthum NL9T (97.2%) and showed 72.3–80.6 % average nucleotide identity and 19.7–29.2 % digital DNA–DNA hybridization identity with the strains of other species of the genus Sphingobium . Strain H33T grew optimally at 30°C, pH 7 and could tolerate 0.5 % (w/v) NaCl. The isoprenoid quinones were ubiquinone-9 (64.1%) and ubiquinone-10 (35.9%). Spermidine was the major polyamine. The major fatty acids of H33T were summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c). The polar lipid profile consisted of a mixture of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, sphingoglycolipid, two unidentified lipids, two unidentified glycolipids, two unidentified aminoglycolipids and an unidentified phospholipid. The genomic DNA G+C content of H33T was 64.9 mol%. Based on the phylogenetic and phenotypic data, H33T was considered a representative of a novel species in the genus Sphingobium . We propose the name Sphingobium nicotianae sp. nov., with H33T (=CCTCC AB 2022073T=LMG 32569T) as the type strain.

Bacterial wilt disease causes heavy yield losses in many crops. Endophytic microbiomes play important roles in control of plant diseases.

A Gram-negative, aerobic bacterial strain, designated LX-88T, was isolated from seleniferous soil in Enshi, Hubei Province, PR China. Strain LX-88Toxidized elemental selenium to selenite, and produced carotenoids but not bacteriochlorophyll. The isolate grew optimally at 28 °C, pH 8.0 and with 0.5 % (w/v) NaCl. Phylogenetic analysies of the organism’s 16S rRNA and bacterial core gene set sequences indicated that LX-88T belongs to the genus Croceibacterium , and has the highest degree of 16S rRNA gene sequence similarity to Croceibacterium soli MN-1T (97.4 %). The LX-88T genome was 3.4 Mbp and had a G+C content of 63.6 mol%. The average nucleotide identity and digital DNA–DNA hybridization values showed low relatedness (below 95 and 70 %, respectively) between strain LX-88T and other strains in the genus Croceibacterium . Ubiquinone-10 was the predominant quinone. The polar lipid profile was dominated by diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid, an unidentified aminolipid, an unidentified phospholipid and an unidentified lipid. The major fatty acid was summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c). These physiological and biochemical tests facilitated the differentiation of strain LX-88T from other members of the genus Croceibacterium . The results of this multifaceted taxonomic study indicate that strain LX-88T represents a novel species in the genus Croceibacterium , for which the name Croceibacterium selenioxidans sp. nov. is proposed. The type strain is LX-88T (=MCCC 1K08007T=LMG 32570T).