Bei Fan

The growth of endophytic bacteria is influenced by the host plants and their secondary metabolites and activities. In this study,P. megateriumP-NA14 andP. megateriumD-HT207 were isolated from potato tuber and dendrobium stem respectively. They were both identified asPriestia megaterium. The antimicrobial activities and metabolites of both strains were explored. For antimicrobial activities, results showed thatP. megateriumP-NA14 exhibited a stronger inhibition effect on the pathogen of dendrobium, whileP. megateriumD-HT207 exhibited a stronger inhibition effect on the pathogen of potato. The supernatant ofP. megateriumP-NA14 showed an inhibition effect only onStaphylococcus aureus, while the sediment ofP. megateriumD-HT207 showed an inhibition effect only onEscherichia coli. For metabolomic analysis, the content ofL-phenylalanine inP. megateriumP-NA14 was higher than that ofP. megateriumD-HT207, and several key downstream metabolites ofL-phenylalanine were associated with inhibition ofS. aureusincluding tyrosine, capsaicin, etc. Therefore, we speculated that the different antimicrobial activities betweenP. megateriumP-NA14 andP. megateriumD-HT207 were possibly related to the content ofL-phenylalanine and its metabolites. This study preliminarily explored why the same strains isolated from different hosts exhibit different activities from the perspective of metabolomics.

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.

In recent years, the prevalence of diabetes is on the rise, globally. Resistant starch (RS) has been known as a kind of promising dietary fiber for the prevention or treatment of diabetes. Therefore, it has become a hot topic to explore the hypoglycemic mechanisms of RS. In this review, the mechanisms have been summarized, according to the relevant studies in the recent 15 years. In general, the blood glucose could be regulated by RS by regulating the intestinal microbiota disorder, resisting digestion, reducing inflammation, regulating the hypoglycemic related enzymes and some other mechanisms. Although the exact mechanisms of the beneficial effects of RS have not been fully verified, it is indicated that RS can be used as a daily dietary intervention to reduce the risk of diabetes in different ways. In addition, further research on hypoglycemic mechanisms of RS impacted by the RS categories, the different experimental animals and various dietary habits of human subjects, have also been discussed in this review.

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.

As an important global crop, the potato (Solanum tuberosum L.) contains the endotoxin solanine that leads to human poisoning and major economic losses. Poisoning symptoms and even acute poisoning may occur when the content of solanine in potatoes exceeds 200 mg/kg. In addition, potatoes are susceptible to some pathogenic bacteria, including Streptomyces scabies and Erwinia carotovora subsp. atroseptica (Van Hall) dye, which can cause potato scab and potato blackleg disease, respectively. In this study, 37 culturable endophytic bacteria strains were obtained from potato tubers based on the culture-dependent method. Results indicated that nine strains showed antimicrobial activity against at least one pathogen by antimicrobial activity screening and 23 strains showed inhibitory activity on solanine in potato tubers. Among them, strain P-NA2-14 (Bacillus megaterium NBRC 15308^T, 99.31%) showed not only better antimicrobial activity against both the two indicator pathogens, but also the best inhibitory activity on solanine, which was proved to be a potential biocontrol bacterium. Meanwhile, the relationship between the distribution of the endophytic bacterial community and the content of solanine in potato tubers was studied by Illumina-based analysis, indicating that the distribution of the endophytic bacterial community was obviously influenced by the content of solanine. The results showed a new insight into the relationship between plant secondary metabolites and endophytic bacteria in potato tubers and provided potential new technical support for the biological control of potato storage.