Abstract The growth of endophytic bacteria is influenced by the host plants and their secondary metabolites and activities. In this study, P. megaterium P-NA14 and P. megaterium D-HT207 were isolated from potato tuber and dendrobium stem respectively. They were both identified as Priestia megaterium . The antimicrobial activities and metabolites of both strains were explored. For antimicrobial activities, results showed that P. megaterium P-NA14 exhibited a stronger inhibition effect on the pathogen of dendrobium, while P. megaterium D-HT207 exhibited a stronger inhibition effect on the pathogen of potato. The supernatant of P. megaterium P-NA14 showed an inhibition effect only on Staphylococcus aureus , while the sediment of P. megaterium D-HT207 showed an inhibition effect only on Escherichia coli . For metabolomic analysis, the content of L -phenylalanine in P. megaterium P-NA14 was higher than that of P. megaterium D-HT207, and several key downstream metabolites of L -phenylalanine were associated with inhibition of S. aureus including tyrosine, capsaicin, etc. Therefore, we speculated that the different antimicrobial activities between P. megaterium P-NA14 and P. megaterium D-HT207 were possibly related to the content of L -phenylalanine and its metabolites. This study preliminarily explored why the same strains isolated from different hosts exhibit different activities from the perspective of metabolomics.
As the unique component of Dendrobium , dendrobine-type sesquiterpenoid alkaloids (DSAs) possess a variety of medicinal properties. It has been well documented that plant endophytes can in vitro synthesize secondary metabolites identical or similar to metabolites produced by their host plants. This study aimed to investigate the composition and distribution of endophytic bacteria of Dendrobium stems by Illumina MiSeq platform sequencing and cultivation-dependent methods and then to assess the potential for endophytic bacteria to produce DSAs. Results indicated that it was necessary to combine both cultivation-dependent and cultivation-independent methods to analyze the community structure of endophytic bacterial in plants comprehensively. The length of the Dendrobium stems influenced the endophytic bacterial community. The diversity and richness of endophytic bacteria in group J10_15cm of stems were the highest, which showed a significant difference from the other stem groups. However, there was no certain connection between the diversity and richness of endophytic bacteria and the content of dendrobine. It was most likely due to the influence of several specific endophytic bacteria genera, such as Sphingomonas and Rhodococcus . Athelia rolfsii , Myrothecium roridum , as pathogenic fungi, and Pectobacterium carotovorum subsp. actinidiae , as pathogenic bacteria of Dendrobium , were used to determine the antimicrobial activities. In these assays, six strains belonging to five genera showed antimicrobial activity against at least two phytopathogens. The strain BL-YJ10_15-29 ( Paracoccus pueri THG-N2.35, 98.98%) showed the best antimicrobial activity against the three phytopathogens. In addition, 2 DSAs (6-hydroxydendrobine and nobilonine) were identified in the fermentation supernatant of the strain CM-YJ10_15-44 ( Pseudomonas protegens CHA0, 99.24%), whereas the whole-genome analysis results further demonstrated that the precursors of the two DSAs [geranyl-PP and (E, E)-famesyl-PP] were synthesized mainly through the methyl-D-erythritol 4-phosphate pathway in this strain. This study provides new insight into the studies on the biosynthesis of DSAs and provides potential biocontrol bacteria.
Abstract The growth of endophytic bacteria is influenced by the host plant and their secondary metabolites and activities. In this study, P-NA14 and D-HT207 were isolated from potato tuber and dendrobium stem respectively. They were both identified as Priestia megaterium . The antimicrobial activities and metabolomic of both strains were explored. For antimicrobial activities, results showed that strain P-NA14 exhibited a better inhibition effect on the pathogen of dendrobium, while strain D-HT207 exhibited a better inhibition effect on the pathogen of potato. The supernatant of strain P-NA14 showed an inhibition effect only on Staphylococcus aureus , while the sediment of strain D-HT207 showed an inhibition effect only on Escherichia coli . For metabolomic analysis, the content of L-phenylalanine in strain P-NA14 was higher than D-HT207, and several key downstream metabolites of L-phenylalanine were associated with inhibition of S_aureus including tyrosine, capsaicin, etc. Therefore, we speculated that the different antimicrobial activities between strain P-NA14 and strain D-HT207 were possibly related to the content of L-phenylalanine and its metabolites. This study provided a preliminary exploration of the fact why different activities appeared on the strains that were identified as the same species but isolated from different hosts at the metabolomic level.
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