Aerobic denitrifying bacteria in the phyllosphere: screening and characterizing of nitrogen removal performance

Abstract:

[Objective] To identify efficient aerobic denitrifying bacteria in the phyllosphere and provide new ideas for the prevention and control of air pollution by phytoremediation. [Methods] We used the enrichment culture method combined with the Griess reagent and bromothymol blue to isolate aerobic denitrifying bacteria from the phyllosphere and analyzed the phylogenetic relationship of the isolates based on the 16S rRNA gene sequences. Efficient aerobic denitrifying bacteria were screened out and their denitrification conditions were optimized. [Results] Thirteen strains were isolated from the phyllosphere of six landscape plant species: Photinia serratifolia, Ligustrum lucidum, Osmanthus fragrans, Camphora officinarum, Euonymus japonicus, and Magnolia grandiflora. According to the 16S rRNA gene sequences, the 13 strains were classified into 7 genera, 7 families of 4 phyla. Specifically, 4, 3, and 2 strains belonged to Enterobacter, Achromobacter, and Pseudomonas, respectively, and the remaining 4 strains belonged to Acinetobacter, Sphingobacterium, Microbacterium, and Pseudarthrobacter. The comparative analysis revealed that strain SF outperformed the other strains in denitrification. The factors (carbon source, temperature, initial pH, C/N ratio, and rotational speed) influencing the denitrification performance of SF were optimized by single factor tests and response surface methodology. The denitrification conditions of SF were optimized as follows: glucose as the carbon source, initial pH 7.5. C/N ratio of 9.7, rotational at 180 r/min, and temperature of 33.5 ℃. Under the optimized conditions, the total nitrogen removal rate reached 93.3% in 72 h when the initial nitrate concentration was 361 mg/L. [Conclusion] The rich culturable aerobic denitrifying bacteria in the phyllosphere of landscape plants laid a foundation for phytoremediation. It is feasible to synergistically reduce nitrogen oxide pollution in the air by screening efficient denitrifying strains and improve the denitrifying performance by optimizing the culture conditions.