Vietnam is recognized as one of the countries with the high diversity of medicinal plant species in the world, nevertheless little is known about the distribution, diversity and biological activity of endophytic actinomycetes associated with host plants. The present study aimed to evaluate antimicrobial and cytotoxic activities of four endophytic Streptomyces strains including Streptomyces sp. HBQ75, HBQ87, HBQ102 and HBQ104 isolated from different organs (roots, stems or leaves) of Cinnamomum cassia Presl. Analysis of 16S rRNA gene sequences and the phylogenetic tree assigned them to four different Streptomyces species as follow Streptomyces fulvissimus HBQ75, Streptomyces parvulus HBQ87, Streptomyces pratensis HBQ102 and Streptomyces ribosidificus HBQ104. These strains exhibited broad antimicrobial spectrum against at least five out of nine pathogens tested, among them S. parvulus HBQ87 showed the best activity (inhibition zones >20 mm). Interestingly, S. parvulus HBQ87 carried all three genes (pks-I, pks-II and nrps) encoding for polyketide synthase or non-ribosomal peptide synthetase enzymes involved in biosynthesis of secondary metabolites, while the remaining strains only possessed one or two genes. All the Streptomyces strains were positive for the anthracyclines-like antibiotic activity. The cell-free supernatants of S. parvulus HBQ87 revealed remarkable inhibitory effects against all three human cacinomar cell lines including hepatoma Hep3B, breast adenocarcinoma MCF7 and lung cancer A549 cells at both concentrations tested (30 µg/mL and 100 µg/mL), while S. fulvissimus HBQ75 and S. pratensis HBQ102 were active against only Hep3B and MCF7 cells. In conclusion, the phenotypic and genotypic features of the four endophytic Streptomyces strains suggest that they have a capacity to produce different broad-spectrum secondary metabolites. Among them, S. parvulus HBQ87 could be the most potential candidate for the production of important antimicrobial and antitumor compounds.
Lactic acid bacteria have been advocated as probiotics to replace antibiotic growth promoters, improve growth performance, and reduce cost production in swine farming. The aim of this study is to identify and evaluate the probiotic traits of strain LCN13 isolated from traditionally fermented feed for swine. Thirty-five bacterial isolates with different morphological characteristics were isolated, among which 9 isolates showed the ability to produce lactic acid and antibacterial activity against pathogenic bacteria. Among them, isolate LCN13 exhibited a strong capacity to produce lactic acid (18.5 ± 0.31 g/L), inhibited gastrointestinal pathogens such as Salmonella typhimurium ATCC 14028 (18.3 ± 1.52 mm), Escherichia coli ATCC 11105 (24.7 ± 2.14 mm), and Staphylococcus epidermidis ATCC 35984 (31.6 ± 2.93 mm), and produced 182 ng/mL folate and 233 ng/mL riboflavin as measured by LC-MS/MS after 24 hours of incubation. Based on morphological, biochemical, and 16S rRNA gene analysis, the isolate LCN13 was identified as Lactobacillus plantarum. Phenotypic analysis revealed that L. plantarum LCN13 showed remarkable resistance to 1.2% ox-bile salt, 2.0 mM H2O2, and pH 3.0. In addition, the ability to produce high levels of folate (253.6 ± 10.7 ng/mL) and riboflavin (312.0 ± 12.2 ng/mL) after 48 hours was exploited for the first time in the L. plantarum. Taken together, L. plantarum LCN13 might serve as a potential probiotic candidate for animal farming.
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