Diversity of plant growth-promoting Paenibacillus mucilaginosus isolated from vegetable fields in Zhejiang, China

Paenibacillus mucilaginosus is a biofertilizer used widely for its P-, K-mineralizing and N-fixing activities. The phenotypic and genotypic diversities of 27 P. mucilaginosus strains or isolates were investigated. The strains had some shared morphological and biochemical characteristics, yet they displayed some diversities. Colony and capsule size varied from 2.00 to 5.72 mm and 200.07 to 857.23 μm, respectively. Polysaccharide production was 2.04–13.12 mg mL, which correlated positively with both capsule (r = 0.714) and colony (r = 0.824) sizes. A pH decrease of 1.21–2.62 was correlated positively with the dissolution of P (r = 0.777) and K (r = 0.778). The dissolved P and K concentrations were 0.05–102.72 mg L and 0.02–27.92 mg L, respectively. The fixed nitrogen concentration was 0.47–18.28 mg L. These bacteria also revealed genotypic diversity at gene, repetitive sequence and genome levels. Altogether, 249 bands were amplified using 18 random amplified polymorphic DNA (RAPD) primers, and the resulting dendrogram showed that the strains were grouped into two clusters according to their origins. Each cluster was divided into two branches: one with higher polysaccharide and acid production, and one with lower production. The gyrB gene and enterobacterial repetitive intergenic consensus (ERIC) gave similar results. In conclusion, as P. mucilaginosus genetic variability described by RAPD and gyrB gene analyses showed some correspondence with polysaccharide and acid diversity, the molecular characterization methods employed in the present study can be utilized in identification of strains with functions in P-, K -mineralizing and N-fixing. Further work is necessary to determine the exact biomarker(s) of these functions.