A total of 2690 actinomycete strains were screened as potential biological control agents in controlling rice bacterial blight (BB) in Vietnam. From these microorganisms, seventeen actinomycete strains were found to be capable of inhibiting all 10 major Xoo races isolated from Xoo-infected rice leaves. One strain, namely VN08-A-12, contained effective characteristics in selectively inhibiting all 10 races in vitro, but did not inhibit most of the other tested microorganisms. Therefore, VN08-A-12 was subsequently selected for rice field trials for two seasons on two rice cultivars SS1 and KD18. Results showed VN08-A-12 was not only able to reduce Xoo lesion lengths in the two rice cultivars (lesion length reduction of up to 38.3 %), but it also significantly reduced Xoo-related yield loss in infected rice cultivars from the field (yield loss reduction of up to 43.2 %). Interestingly, the culture of this strain also increased the rice yield in healthy rice cultivars (from 2.66 % to 16.98 % for SS1 and from 3.11 % to 5.94 % for KD18 cultivar). The strain VN08-A-12 was shown to be identical to Streptomyces toxytricini. To our knowledge, this is the first study reporting S. toxytricini as a beneficial biological agent for the control of BB in rice.
Dolomite is a double salt composed of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). The heat treatment of CaCO3 and MgCO3 respectively generates calcium oxide (CaO) and magnesium oxide (MgO), which have antimicrobial activity. In this study, heated dolomite powder (HDP) slurry was investigated for its sporicidal activity against Bacillus subtilis ATCC 6633 spores. The B. subtilis spores used in this study were not affected by acidic (pH 1) or alkaline (pH 13) conditions, indicating that they were highly resistant. However, dolomite powder heated to 1000℃ for 1 h could kill B. subtilis spores, even at pH 12.7. Sporicidal activity was only apparent when the dolomite powder was heated to 800℃ or higher, and sporicidal activity increased with increases in the heating temperature. This temperature corresponded to that of the generation of CaO. We determined that MgO did not contribute to the sporicidal activity of HDP. To elucidate the sporicidal mechanism of the HDP against B. subtilis spores, the generation of active oxygen from HDP slurry was examined by chemiluminescence analysis. The generation of active oxygen increased when the HDP slurry concentration rose. The results suggested that, in addition to its alkalinity, the active oxygen species generated from HDP were associated with sporicidal activity.
A novel competition model developed with the new logistic model and the Lotka-Volterra model successfully predicted the growth of bacteria in mixed culture using the mesophiles Staphylococcus aureus, Escherichia coli, and Salmonella at a constant temperature in our previous studies. In this study, we further studied the prediction of the growth of those bacteria in mixed culture at dynamic temperatures with various initial populations with the competition model. First, we studied the growth kinetics of the species in a monoculture at various constant temperatures ranging from 16℃ to 32℃. With the analyzed data in the monoculture, we then examined the prediction of bacterial growth in mixed culture with two and three species. The growth of the bacteria in the mixed culture at dynamic temperatures was successfully predicted with the model. The residuals between the observed and predicted populations at the data points were <0.5 log at most points, being 83.3% and 84.2% for the two-species mixture and the three-species mixture, respectively. The present study showed that the model could be applied to the competitive growth in mixed culture at dynamic temperature patterns.
Bacillus cereus is a spore-forming bacterium. B. cereus occasionally causes nosocomial infections, in which hand contamination with the spores plays an important role. Therefore, hand hygiene is the most important practice for controlling nosocomial B. cereus infections. This study aimed to determine the appropriate hand hygiene procedure for removing B. cereus spores. Thirty volunteers’ hands were experimentally contaminated with B. cereus spores, after which they performed 6 different hand hygiene procedures. We compared the efficacy of the procedures in removing the spores from hands. The alcohol-based hand-rubbing procedures scarcely removed them. The soap washing procedures reduced the number of spores by more than 2 log10. Extending the washing time increased the spore-removing efficacy of the washing procedures. There was no significant difference in efficacy between the use of plain soap and antiseptic soap. Handwashing with soap is appropriate for removing B. cereus spores from hands. Alcohol-based hand-rubbing is not effective.
Kudoa septempunctata in olive flounder meat was inactivated using 3 distinct freezing methods： liquid freezing for 5 min, air blast freezing at －30℃ for 5 h, and －80℃ for 1 h. The fracture curve of olive flounder meat subjected to liquid freezing resembled that of meat stored at 4℃, indicating that the structure of olive flounder muscle was well preserved. In contrast, air blast freezing induced the disappearance of the fracture point in the fracture curve, indicating that there was deterioration in the meat quality. Liquid freezing preserved the transparency of olive flounder meat to the same degree as that of meat stored at 4°C. However, air blast freezing induced meat cloudiness. These results indicate that liquid freezing can be used for K. septempunctata inactivation without affecting the meat quality.
We offer the first description of the development of a multiple detection technique for fungi by DNA microarray with the simultaneous use of internal transcribed spacer region (ITS) of ribosomal RNA gene and β-tubulin gene probes. The assay uses 12 oligonucleotide probes and multiplex amplification to detect fungal species belonging to various sections of Aspergillus, the Eurotium genus, and the Penicillium genus. The specificity of each probe was tested using 231 reference fungal strains, including 79 target and 152 non-target strains in 102 species of 24 genera. We determined the optimum concentration of the primer pairs for multiplex PCR to be 0.5 μM for the β-tubulin gene and 0.125 μM for the ITS region. In the field trial using 76 specimens containing 323 fungi (up to five fungal strains were included in one specimen), the concordance rate between the DNA microarray and the DNA sequencing results was 97.4％ at the species or genus levels.
Scanning electron microscopy revealed that the rpoS-deficient cells of E. coli K-12 BW25113 (ΔrpoS) increased the number of flagella on the cell surfaces. However, the quantitative analysis of cell colonization showed that the increased number of flagella on ΔrpoS cell surfaces did not cause the enhancement of cell colonization on the surfaces of polyvinyl chloride (PVC), polypropylene (PP) and polystyrene (PS) after 24 h of incubation at 37℃. To facilitate the enhanced expression of curli, the csgA gene was introduced into the ΔrpoS cells. The transformed cells rich in flagella and curli on the cell surfaces were found to make colonies 2-3 times larger than both the wild type and ΔrpoS cells on the PVC, PP and PS surfaces at 37℃. It was thus verified that the reinforcement of csgA gene in the ΔrpoS cells induced the enhanced colonization on the solid surfaces with the increased flagellum and curli expressions.
We examined amino acid requirements for the growth of the halotolerant Brevibacterium sp. JCM 6894 in the absence and presence of 1.2 M NaCl in a chemically defined medium. The experiment was also carried out in the presence of 1.2 M KCl. As a result, growth was highly enhanced by methionine in the absence and presence of KCl as well as NaCl up to 1.2 M. However, growth in the presence of 150 mM methionine was repressed by leucine (up to 100 mM） and valine (up to 100 mM). Concentration-dependent growth inhibition was observed in the presence of isoleucine (up to 150 mM) and threonine (up to 300 mM). When the cells were incubated in the absence of externally added K+, growth was strongly repressed, even in the presence of 150 mM methionine. The growth, however, recovered drastically by the addition of 1 mM KCl, regardless of the presence and absence of 1.2 M NaCl. These results indicate that methionine, which seems to be symported into cytoplasm with K+, plays an important role in the growth of the strain under salt stress.