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The increasing demands for crop production have become a great challenge while people also realizing the significance of reductions in synthetic chemical fertilizer use. Plant growth-promoting rhizobacteria (PGPR) are proven biofertilizers for increasing crop yields by promoting plant growth via various direct or indirect mechanisms. Siderophilic bacteria, as an important type of PGPR, can secrete siderophores to chelate unusable Fe3+ in the soil for plant growth. Siderophilic bacteria have been shown to play vital roles in preventing diseases and enhancing the growth of plants. Paris polyphylla var. yunnanensis (PPVY) is an important traditional Chinese herb. However, reports about its siderophilic bacteria are still rare. This study firstly isolated siderophilic bacteria from the rhizosphere soil of PPVY, identified by morphological and physio-biochemical characteristics as well as 16S rRNA sequence analysis. The dominant genus in the rhizobacteria of PPVY was Bacillus. Among 22 isolates, 21 isolates produced siderophores. The relative amount of siderophores ranged from 4 to 41%. Most of the isolates produced hydroxamate siderophores and some produced catechol. Four isolates belonging to Enterobacter produced the catechol type, and none of them produced carboxylate siderophores. Intriguingly, 16 strains could produce substances that have inhibitory activity against Candida albicans only in an iron-limited medium (SA medium). The effects of different concentrations of Fe3+ and three types of synthetic chemical fertilizers on AS19 growth, siderophore production, and swimming motility were first evaluated from multiple aspects. The study also found that the cell-free supernatant (CFS) with high siderophore units (SUs) of AS19 strain could significantly promote the germination of pepper and maize seeds and the development of the shoots and leaves of Gynura divaricata (Linn.). The bacterial solution of AS19 strain could significantly promote the elongation of the roots of G. divaricata (Linn.). Due to its combined traits promoting plant growth and seed germination, the AS19 has the potential to become a bioinoculant. This study will broaden the application prospects of the siderophilic bacteria-AS19 as biofertilizers for future sustainable agriculture.

We explored the metabolic mechanism of silkworm(Bombyx mori) to NaF by using the fluoride-tolerant silkworm variety named T6 and the fluoride-sensitive variety named 734 as materials.We fed the silkworm larvae from the first day of fifth instar with mulberry leaves soaked in 50,100,200 and 400 mg/kg NaF solutions respectively.Then we examined the activities of CarE and esterase in hemolymph.Results showed that the activity of CarE was 73% to 88% in 734 strain and 72% to 81% in T6 strain compared with control groups,respectively.The CarE activity of two low concentration NaF-treated 734 groups showed extremely significant differences(P0.01) with control group and two high concentration NaF-treated groups,while the differences among T6′s all treatment groups were not significant.The esterase activity of NaF-treated groups was 89% to 97% in 734 strain and 73% to 92% in T6 strain compared with control groups,respectively.The esterase activity among all treatment groups in 734 strain show no significant differences.The esterase activity of the highest concentrations NaF-treated group showed extremely significant differences(P0.01) compared with control group.These results suggest that the fluoride has certain inhibition to the activity of CarE and esterase in hemolymph of silkworm.