Microbial radiosensitization using combined treatments of essential oils and irradiation- part B: Comparison between gamma-ray and X-ray at different dose rates.

Stored rice and rice products are prone to contamination by pathogenic fungi and bacteria such as Aspergillus niger, Bacillus cereus, and Paenibacillus amylolyticus. Treatment with antimicrobial essential oils (EOs) and irradiation are options to control spoilage organisms. Microbial samples with or without fumigation with an oregano/thyme EO mixture were irradiated at 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 kGy for calculation of a D10 value. The relative sensitivity was calculated as the ratio of D10 values for the irradiation plus oregano and thyme EO combination and irradiation alone treatments. In all cases, irradiation plus fumigation with the oregano and thyme EO mixture showed increased efficacy compared with irradiation alone. The relative sensitivity of γ-ray irradiation against A. niger was 1.22, 1.33, and 1.24 for radiation dose rates of 10.445, 4.558, and 0.085 kGy/h, respectively, however against B. cereus it was 1.28, 1.45, and 1.49, and against P. amylolyticus it was 1.35, 1.33, and 1.38, for respective γ-ray irradiation dose rates. The relative sensitivity of X-ray irradiation against A. niger, B. cereus, and P. amylolyticus was 1.63, 1.21, and 1.31, respectively, at the X-ray dose rate of 0.76 kGy/h. The results showed that the relative sensitivity of γ-ray irradiation was higher against the two bacteria than the fungus, whereas X-ray showed higher sensitivity against the fungus than the two bacteria. There was no consistent positive or negative relationship between dose rate and relative sensitivity. The results demonstrated the potential of an oregano and thyme EOs mixture as an antimicrobial agent and its efficacy to increase the radiosensitization of A. niger, B. cereus, and P. amylolyticus during γ-ray or X-ray irradiation treatments.

Paenibacillus albus sp. nov., a UV radiation-resistant bacterium isolated from soil in Korea.

A novel Gram-stain-positive, motile, white color and endospore-forming bacterium, designated 18JY67-1T, was isolated from soil in Jeju Island, Korea. The strain grow at 15-42 °C (optimum 30 °C) in R2A medium at pH (6.0-9.5) (optimum 7.5). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 18JY67-1T formed a distinct lineage within the family Paenibacillaceae (order Bacillales, class Bacilli), and was closely related to Paenibacillus rhizoryzae (KP675984; 96.9% 16S rRNA gene sequence similarity). The major cellular fatty acids of the strain 18JY67-1T were C16:0 and anteiso-C15:0. The predominant respiratory quinones were MK-7. The major polar lipid was identified as diphosphatidylglycerol. On the basis of phenotypic, chemotaxonomic and genotypic properties clearly indicated that isolate 18JY67-1T represents a novel species within the genus Paenibacillus, for which the name Paenibacillus flavus sp. nov. is proposed. The type strain of Paenibacillus flavus is 18JY67-1T (= KCTC 33959T = JCM 33184T).

Comparison of the spores of Paenibacillus polymyxa prepared at different temperatures.

Paenibacillus polymyxa SQR-21, which is antagonistic against Fusarium oxysporum, is used as a biocontrol agent and, when mixed with organic substances for solid fermentation, produces a bioorganic fertilizer. The spores of P. polymyxa prepared at different temperatures were characterized with respect to the dipicolinic acid content, heat resistance, fatty acid composition and germination. Spores prepared at 37°C showed higher heat resistance than those prepared at 25 and 30°C. However, the germination rate was negatively correlated with the sporulation temperature. The maximum germination rate of the spores prepared at 25°C was 1.3-times higher than the spores prepared at 30°C. The sporulation temperature thus affects the resistance and germination properties of P. polymyxa spores. These results are useful for the production of improved bio-organic fertilizer.

Radiation inactivation of Paenibacillus larvae and sterilization of American Foul Brood (AFB) infected hives using Co-60 gamma rays.

The effectiveness of gamma radiation in inactivating the Philippine isolate of Paenibacillus larvae was investigated. Spores of P. larvae were irradiated at incremental doses (0.1, 0.2, 0.4, 0.8 and 1.6 kGy) of gamma radiation emitted by a 6°Co source. Surviving spores were counted and used to estimate the decimal reduction (D10) value. A dose of 0.2 kGy was sufficient to inactivate 90% of the total recoverable spores from an initial count of 105- 9 × 10³ spores per glass plate. The sterilizing effect of high doses of gamma radiation on the spores of P. larvae in infected hives was determined. In this study, a minimum dose (D(min)) of 15 kGy was tested. Beehives with sub-clinical infections of AFB were irradiated and examined for sterility. All the materials were found to be free of P. larvae indicating its susceptibility to γ-rays. After irradiation, there were no visible changes in the physical appearance of the hives' body, wax and frames. Thus, a dose of 15 kGy is effective enough for sterilization of AFB-infected materials.