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• Characterization of An Actinomycete Strain with Bioactivity against Vibrio parahaemolyticusCausing Disease on Shrimp

  Nguyen Xuan Canh, Ho Tu Cuong, Nguyen Thi Dinh, Pham Thi Hieu

  Date Received: 12-07-2016 / Date Accepted: 20-11-2016 / Date Published: 13-06-2025

   Abstract PDF (VIETNAMESE)

  An experiment was conducted to screen and identify the actinomycete trains that are capable of antagonizing Vibrio parahaemolyticuscausing disease on shrimp. Among of 96 isolated strains, three strains were obtained as capable of antagonizing Vibrio parahaemolyticusby agar diffusion plate method. The strain number 25.2 had strongest activity with a diameter of 15 mm clear zone of bacteria. The 25.2 strain showed white colonies but white colonies with grey borders after three and seven days of incubation, respectively. The strain did not produce soluble pigments on Gause-1 medium but grew well at temperatures between 30 - 45°C and neutral pH, and was tolerant to high salt concentration medium. The 25.2 strain was able to utilize several sources of carbon and nitrogen. Results of 16S rRNA sequence analysis showed that the strain 25.2 had a similarity of 96% compared with Streptomyces aureofaciens. Based on morphological characteristics, culture, physiological and biochemical characteristics and molecular biological analyses, the strain 25.2 was identified as Streptomyces aureofaciens.

  DOI: https://doi.org/10.31817/tckhnnvn.2016.14.11.

• Investigation of Antibacterial Activity of Vietnamese Oregano (Elsholtzia ciliate) Essential Oil Against some Pathogenic Bacteria Strains in Freshwater Fish

  Tong Nhut Nam, Dang Quoc Vinh, Vo Nguyen Khang Tuyen, Tran Thi My Dung, Ho Thi Truong Thy, Ong Moc Quy

  Date Received: 03-09-2025 / Date Accepted: 02-12-2025 / Date Published: 23-01-2026

   Abstract PDF (VIETNAMESE)

  This study evaluated the antibacterial activity of essential oil from Vietnamese balm (Elsholtzia ciliata) against three pathogenic bacteria in freshwater cultured fish: Aeromonas hydrophila (Att1), Edwardsiella ictaluri (Ecd20), and Streptococcus agalactiae (Svb2). The essential oil was extracted using microwave-assisted steam distillation and its chemical composition was analyzed by GC-MS. Experiments with microwave treatment times of 2-8 minutes, 500W power, and oil concentrations of 5-15% showed that antibacterial efficacy increased with both concentration and treatment duration. Ecd20 was the most sensitive strain (31.7mm inhibition zone at 15% after 8 minutes), followed by Att1 (18mm), while Svb2 was less sensitive but still showed significant inhibition. The MIC values for Ecd20, Svb2, and Att1 were 0.39, 0.78, and 1.56 mg/ml, respectively. Chemical analysis identified Linoleic acid (26.64%), Oleic acid (16.97%), Citral (10.9%), beta-cis-Ocimene (7.38%), and beta-Caryophyllene (7.56%) as major constituents likely contributing to the bioactivity. The results confirmed that microwave treatment enhances the antibacterial effect, particularly evident at 8 minutes. This study provides scientific evidence linking chemical composition and biological activity, and suggests the potential application of E. ciliata essential oil as a natural alternative to antibiotics in aquaculture.

  DOI: https://doi.org/10.31817/tckhnnvn.2026.24.1.05

• Isolation and Selection of Microorganism for Treatment of Post-harvest by-Products of Green Ramie (Boehmeria nivea (L.) Gaudich)

  Dinh Hong Duyen, Lo Van Son

  Date Received: 03-06-2025 / Date Accepted: 09-09-2025 / Date Published: 30-09-2025

   Abstract PDF (VIETNAMESE)

  This study aimed to select a microbial consortium for developing a bio-product for treatment of post-harvest by-products of green ramie (Boehmeria nivea (L.) Gaudich) into raw materials for organic fertilizer production. Microorganisms were isolated by serial dilution and cultured on selective media for cellulose-degrading strains, followed by screening under different cultivation conditions. Four selected strains, Penicillium sp.N5, Streptomyces sp.X6, Bacillus sp.V14, and Bacillus sp.V24, exhibited cellulase activity of 18.1-25.0mm, CMCase activity of 16.7-22.4mm, amylase activity of 11.7-18.0mm, and protease activity of 18.2-20.4mm. These strains maintained growth and enzyme activities (cellulase, CMCase, amylase, protease) at pH 4-8 and temperatures of 20-60C, and demonstrated streptomycin resistance at 300-1,000 mg/l. Composting trials using the selected microbial consortium achieved a maximum temperature of 52C after 5 days, with total nitrogen content of the composted material reaching 0.21-0.35% and C/N ratio 74.6-130.7, after 35 days. The final product met the criteria for use as raw material in organic fertilizer production.

  DOI: https://doi.org/10.31817/tckhnnvn.2025.23.9.06

• Research on Using Endophytic Bacteria Isolated from Different Ecosystems

  Nguyen Hai Van, Nguyen Thi Minh

  Date Received: 03-05-2017 / Date Accepted: 14-06-2017

   Abstract PDF (VIETNAMESE)

  The aim of this study was to select and use the endophytic microorganism strains from different ecosystems for the production of multifunctional biofertilizer formulation for crop plants. The endophytic microorganisms were selected for their IAA and hydrolytic enzyme production, phosphorus solubilization, and antagonism to pathogenic microorganims. Six endophytic bacterial strains, 3TDG1, 3TDG4, 3TDG5, 3LC2, 3LDQ2 and 3CL2, with high bioactivity were selected from 32 endophytic bacteria strains. These strains were used for adding into the nutrient liquid obtained from treatment of livestock waste for the production of multifunctional biofertilizer formulation. These strains were 99% homologous with Klebsiella pneumoniae strain PSB1, Klebsiella oxytoca strain ALK033, Aeromonas caviae strain J5; Pseudomonas putida strain E1-4, Pantoea rodasii strain Y36 and Bacillus subtilis strain QB5413, respectively. The yield of Basella alba L. in tetsting experiment fertilized with multifunctional formulation increased by 89.51% as compared with the use of NPK fertilizer.