Search

The conidia of Pyricularia oryzae were cultured on barley grain medium for 17 days in this study. Two hundred milliliters of barley grains of each tested strain were cultured in a 500 mL Erlenmeyer flask. The conidia were eluted with 300 mL of sterile water from the cultivated barley grains in each flask. The barley grains were placed in aluminum plates for continued cultivation. The conidia were eluted with 48 h of interval culture, and the elution method used each time was the same as that used for the first elution. All the tested strains could be eluted 6 times; thus, we obtained a large number of conidia. The numbers of conidia produced in the elutions of all the strains were significantly different, with the smallest number produced in the first elution, followed by a gradual increase and then a gradual decrease after reaching the peak; the number of conidia produced in the sixth elution, that is, the final elution, was also low. The total number of conidia and the total number of effective conidia differed among the strains. A large number of effective conidia can be obtained by using the method described in this study, and much time can be saved because the conidia can be eluted six times in one culture cycle. [ABSTRACT FROM AUTHOR]

The objective of this study was to preliminarily analyze the differences in pathogenicity and physiologic races between Pyricularia oryzae isolates from indica and japonica rice varieties. Five to 7 isolates of P. oryzae from indica and japonica, having good sporulation capacity, were screened out in each experimental year. To determine the pathogenicity of P. oryzae, different kinds of rice varieties were inoculated with mixtures of indica and japonica isolates. A total of 46 isolates, including 23 indica isolates and 23 japonica isolates, were screened out in four years. In total, 1252 rice varieties, including 490 indica, 296 japonica and 466 indica-japonica hybrid rice varieties, were inoculated. Our results suggested that the degree of disease was more severe in most indica varieties infected with indica isolates than in those infected with japonica isolates. That is, indica isolates were more inclined to infect indica varieties. A majority of japonica and indica-japonica hybrid rice varieties infected with japonica isolates showed more severe infection than those infected with indica isolates. In other words, japonica isolates more easily infected japonica and indica-japonica hybrid rice varieties. The differences in quantity among the varieties indicated high resistance to rice blast in the corresponding kinds of rice inoculated with indica and japonica isolates, fully explaining the above viewpoint. Most of the 23 indica isolates belonged to indica races. Among the 23 japonica isolates, half were indica races and half were japonica races. In addition, there were significant differences between the isolates selected in the first two years and those selected in the second two years. The isolates in the first two years were all of indica races, and those of japonica races all appeared in the second two years. The results showed that the race of isolates shared little association with the kind of rice variety collected but was associated with the year of neck blast sample collection. [ABSTRACT FROM AUTHOR]

Contamination control and removal are very important technical aspects of microbiological research. Bacterial contamination is very common in fungal cultures. Currently, the commonly used approach for inhibiting bacteria is antibiotic treatment; however, there are drawbacks to using antibiotics, including incomplete removal, limited antibacterial spectra, tendency toward recontamination, effects to fungal strains, and potential risks to the environment. Therefore, in the present work, we developed a new method for bacterial removal from fungi cultured on solid medium, the Cabin-Sequestering (CS) method, based on the different culture characteristics between fungi and bacteria. First, 3–5 mm round or square holes (the "cabin") are excavated on a solid medium plate. The fungal strain containing possible bacterial contamination is inoculated into the cabin. The cabin is then covered with a sterilized coverslip, followed by incubation at the appropriate temperature. After 7–10 days of culturing, fungal hyphae grow out along the edge of the coverslip; however, the contaminating bacteria cannot pass through the space formed between the medium and the coverslip and, thus, remain in the cabin. The newly grown fungal hyphae around the coverslip are re-inoculated into fresh culture plates, where they form bacteria-free fungal colonies. The CS method is easy handling, with a short experimental cycle and rare recontamination. When necessary, it can also be used in combination with antibiotics in bacterial removal operations. [ABSTRACT FROM AUTHOR]

Thiamin diphosphate (ThDP) analogs have been designed and synthesized based on the ThDP binding site of the pyruvate dehydrogenase multienzyme complex E1 of Escherichia coli. This study investigated the effect of 66 novel ThDP analogs on rice bacterial brown stripe pathogen Acidovorax avenae subsp. avenae strain RS-1. Results indicated that three of the 66 ThDP analogs (designated as 20, 21 and 53) significantly inhibited the in vitro growth of strain RS-1. However, no obvious cell lysis and destruction was found for this rice pathogenic bacterium, which were supported by morphological evidence of transmission electron microscope. In contrast, the three ThDP analogs significantly reduced biofilm formation and the activity of the pyruvate dehydrogenase of strain RS-1. Furthermore, the differential expression of ThDP target gene and 20 secretion system related genes were revealed by using quantitative real-time PCR. Among these, the expressions of ThDP target gene and VgrG-5 under the treatment of ThDP 20 were strongly induced compared to the control, which indicated that the antibacterial mechanism of ThDP analogs may be mainly due to the changed expression of ThDP target gene and secretion system related genes rather than causing damage to cell membrane. Taken together, the application of synthesized ThDP analogs might be a tractable strategy to overcome the pathogen of rice bacterial brown stripe. [ABSTRACT FROM AUTHOR]

Bacillus strains are broadly studied for their beneficial role in plant growth and biological control of plant disease and pest; however, little is known about their underlying mechanisms. In this study, we assessed the controlling and defence-related mechanisms of three Bacillus strains including rice seed-associated strain B. subtilis A15, rhizobacterial strains B. amyloliquefaciens D29 and B. methylotrophicus H8, all of which are against bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae. Results indicated that all three strains showed strong biofilm formation ability. The culture filtrates of each strain significantly suppressed the growth and biofilm formation of X. oryzae, while changes in bacterial cell morphology such as cell swell and severe cell wall alterations were observed through the transmission electron microscopy images. PCR analysis revealed that all three strains harbour the antimicrobial-associated genes that are responsible for biosynthesis of bacillomycin, fengycin, iturin and surfactin. Subsequent real-time qPCR analysis revealed the upregulated expression of fenD and srfAA genes in D29 and H8, and fenD and ituC genes in A15 during their in vitro interaction with X. oryzae. It suggests that the antibacterial mechanisms of the three strains may be at least partially associated with their ability to secrete corresponding lipopeptides. Interestingly, the applications of the three strains in greenhouse conditions were found to be effective in controlling the BLB disease, which was achieved through the activation of inducing systemic resistance resulted from the enhanced activities of defence-related enzymes. This is the first report of demonstration of the mode of antibacterial effect of Bacillus strains against X. oryzae. Overall, data from the current study provide valuable information for biological control of BLB disease in rice. [ABSTRACT FROM AUTHOR]

This present study deals with synthesis, characterization and antibacterial activity of cross-linked chitosan-glutaraldehyde. Results from this study indicated that cross-linked chitosan-glutaraldehyde markedly inhibited the growth of antibiotic-resistant Burkholderia cepacia complex regardless of bacterial species and incubation time while bacterial growth was unaffected by solid chitosan. Furthermore, high temperature treated cross-linked chitosan-glutaraldehyde showed strong antibacterial activity against the selected strain 0901 although the inhibitory effects varied with different temperatures. In addition, physical-chemical and structural characterization revealed that the cross-linking of chitosan with glutaraldehyde resulted in a rougher surface morphology, a characteristic Fourier transform infrared (FTIR) band at 1559 cm-1, a specific X-ray diffraction peak centered at 2? = 15°, a lower contents of carbon, hydrogen and nitrogen, and a higher stability of glucose units compared to chitosan based on scanning electron microscopic observation, FTIR spectra, X-ray diffraction pattern, as well as elemental and thermo gravimetric analysis. Overall, this study indicated that cross-linked chitosan-glutaraldehyde is promising to be developed as a new antibacterial drug. [ABSTRACT FROM AUTHOR]

The effect of rhizobacterium Burkholderia sp. strain R456 on the inhibition of Rhizoctonia solani, sheath blight of rice was examined. Results from this study indicated that strain R456 not only suppressed the in vitro mycelial growth of R. solani, but also reduced the incidence and severity of rice sheath blight under greenhouse conditions. However, similar to plant pathogenic strain LMG 1222 of Burkholderia cepacia, the type species of the genus, infiltration of tobacco leaves with cell suspension of strain R456 resulted in typical hypersensitivity reactions while the two bacterial strains were unable to cause disease symptoms on rice seedlings. The fatty acid methyl ester profile, sole carbon source utilization, and biochemical tests confirmed that the antagonistic rhizobacterium R456 is a member of the genus Burkholderia. Furthermore, strain R456 was differentiated from B. cepacia LMG 1222 and was identified as Burkholderia seminalis based on recA gene sequence analysis and multilocus sequence typing. In addition, this rhizobacterium had a lower proteolytic activity compared with that of the pathogenic B. cepacia LMG 1222 while no cblA and esmR marker genes were detected for the two bacterial strains. Overall, this is the first characterization of rhizobacterium B. seminalis that protected rice seedlings from infection by R. solani. [ABSTRACT FROM AUTHOR]

The peroxisomal matrix proteins involved in many important biological metabolism pathways in eukaryotic cells are encoded by nucleal genes, synthesized in the cytoplasm and then transported into the organelles. Targeting and import of these proteins depend on their two peroxisomal targeting signals (PTS1 and PTS2) in sequence as we have known so far. The vectors of the fluorescent fusions with PTS, i.e., green fluorescence protein (GFP)-PTS1, GFP-PTS2 and red fluorescence protein (RFP)-PTS1, were constructed and introduced into Magnaporthe oryzae Guy11 cells. Transformants containing these fusions emitted fluorescence in a punctate pattern, and the locations of the red and green fluorescence overlapped exactly in RFP-PTS1 and GFP-PTS2 co-transformed strains. These data indicated that both PTS1 and PTS2 fusions were imported into peroxisomes. A probable higher efficiency of PTS1 machinery was revealed by comparing the fluorescence backgrounds in GFP-PTS1 and GFP-PTS2 transformants. By introducing both RFP-PTS1 and GFP-PTS2 into Δ mgpex6 mutants, the involvement of MGPEX6 gene in both PTS1 and PTS2 pathways was proved. In addition, using these transformants, the inducement of peroxisomes and the dynamic of peroxisomal number during the pre-penetration processes were investigated as well. In summary, by the localization and co-localization of PTS1 and PTS2, we provided a useful tool to evaluate the biological roles of the peroxisomes and the related genes. [ABSTRACT FROM AUTHOR]