A novel tumor-targeting strain of Xenorhabdus stockiae exhibits potent biological activities.

Xenorhabdus are symbionts of soil entomopathogenic nematodes of the genus Steinernema presenting two distinct forms in their life cycle, and can produce a broad range of bioactive compounds. In this study, a novel Xenorhabdus stockiae strain HN_xs01 was isolated from a soil sample via an entrapment method using Galleria melonella nematodes. The supernatants of strain HN_xs01 exhibited antimicrobial properties against Gram-negative and Gram-positive bacteria, and insecticidal properties against Helicoverpa armigera larvae, and antitumor properties as well. Moreover, three linear rhabdopeptides (1, 2 and 3) were identified from strain HN_xs01 using nuclear magnetic resonance analysis, which exhibited significant cytotoxic activity against the human epithelial carcinoma cell line A431 and the human chronic myelogenous leukemia cell line K562. Some bacteria have been reported to colonize the tumor region, and we determined that HN_xs01 could grow in tumor xenografts in this study. HN_xs01 invaded and replicated in B16 melanoma cells grafted into C57BL/6 mice, resulting in tumor inhibition. Moreover, strain HN_xs01 not only merely aggregated in the tumor environment, but also prevented pulmonary metastasis. It caused fragmentation of vessels and cell apoptosis, which contributed to its antitumor effect. In conclusion, X. stockiae HN_xs01 is a novel tumor-targeting strain with potential applications in medicinal and agricultural fields.

[Isolation, identification and characterization of five Pseudomonas strains].

OBJECTIVE: We isolated Pseudomonas strains from soil samples collected from Changsha, Hunan province, catalogued them and studied the antimicrobial and antitumor activity. METHODS: We isolated Pseudomonas strains from soil samples through Galleria bait method, identified and catalogued the isolated strains according to morphological observation, physiological and biochemical characteristics and the homologous analysis of 16S rRNA sequences of nucleotides. Antimicrobial, antagonistic fungi and anti-tumor activities were studied by diffusion plate assay, dual-culture assay and cytotoxicity test respectively. RESULTS: We isolated 5 Pseudomonas strains from vegetable field and forest land of Changsha suburb, catalogued and named them as Pseudomonas protegens CY01, Pseudomonas chlororaphis CY02, Pseudomonas oryzihabitans CY04, Pseudomonas sp. CY05 and Pseudomonas putida CY06 respectively. P. protegens CY01 and P. chlororaphis CY02 have antibacterial activity against Bacillus subtillis and Staphylococcus aureus. P. chlororaphis CY02 has antagonistic activity against Pyricularia oryzae and anti-tumor cell activity against mouse melanoma B16 cells. CONCLUSION: The isolated P. chlororaphis CY02 has a significant effect on pathogenic bacteria, Pyricularia oryzae and tumor cells.