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Antagonistic activity of microorganisms against phytopathogens is mainly the results of plants’ health improvement due to the inhibition of pathogens growth and the induction of plants resistance against diseases. The aim of the research was to determine antagonistic properties of Pantoea agglomerans against Rhizoctonia solani. The properties of two strains P. agglomerans BC17 and BC45 were assessed according to the following criteria: mycelial growth of R. solani in the presence of bacterial metabolites, an impact of P. agglomerans on the growth of sugar beet in the pots containing soil with and addition of R. solani and without it, the ability to produce indole-3-acetic acid (IAA). It has been recorded that antagonistic properties of tested strains are different. In the presence of metabolites of BC17 strains, the mycelial growth of R. solani was inhibited by 78 % and for the strain BC45 the value amounted 46 %. In the pot bioassay the number of infested plants growing in the soil inoculated with P. agglomerans and the pathogen was lower when compared with the pots containing R solani. A higher reduction of infested plants, amounting 23 %, was obtained for the strain BC17. Both strains had the ability to produce IAA - a plant hormone of the auxin class, in the presence of tryptophan and its absence in the medium. The highest concentration of IAA was recorded after 7 days of culturing in the supernatant obtained from the media containing 2000 μg/cm3 of tryptophan. For the strain BC17 the concentration of IAA marked in the post - culturing liquid amounted 71.57 μg/cm3, and for the BC45 strain it amounted over 80 μg/cm3. Obtained results prove that P. agglomerans may be used in the biological protection against phytopatogenic strains of R. solani.
Rabbits exposed repeatedly to aerosols of endotoxin-containing microvesicles (ECMV) of the outer membrane of the Pantoea agglomerans strain isolated from airborne grain dust showed a large increase in the concentration of circulating cytokines: total interferon (IFN), interleukin-1 alpha (IL-1 alpha), and tumor necrosis factor alpha (TNF alpha). The increase was significantly higher compared to animals exposed to control saline (p<0.001). Aerosol exposure to ECMV also induced the formation of specific precipitin antibodies and lymphocyte activation. The results indicate strong immunomodulative properties of ECMVs produced in nature by Pantoea agglomerans bacteria, and heavily contaminating organic dusts.
Microbiological air sampling was performed on 5 flax farms located in eastern Poland. Air samples for determination of the concentrations of microorganisms, dust and endotoxin were collected in barns during machine scutching of flax stems by the farmers. The concentrations of mesophilic bacteria ranged from 203.5-698.8 × 103 cfu/m3, of Gram-negative bacteria from 27.2-123.4 × 103 cfu/m3, of thermophilic actinomycetes from 0.5-2.6 × 103 cfu/m3, and of fungi from 23.4-99.8 × 103 cfu/m3. The concentrations of total airborne microorganisms (bacteria + fungi) were within a range of 245.0-741.0 × 103 cfu/m3. The values of the respirable fraction of total airborne microflora on the examined farms were between 45.5-98.3%. Corynebacteria (irregular Gram-positive rods, mostly Corynebacterium spp.) were dominant at all sampling sites, forming 46.8-67.8% of the total airborne microflora. Among Gram-negative bacteria, the most numerous species was Pantoea agglomerans (synonyms: Erwinia herbicola, Enterobacter agglomerans), known to have strong endotoxic and allergenic properties. Among fungi, the allergenic species Alternaria alternata prevailed. Altogether, 25 species or genera of bacteria and 10 species or genera of fungi were identified in the farm air during flax scutching; of these, 11 and 6 species or genera respectively were reported as having allergenic and/or immunotoxic properties. The concentrations of airborne dust ranged within 43.7-648.1 mg/m3 (median 93.6 mg/m3), exceeding on all farms the Polish OEL value of 4 mg/m3. The concentrations of airborne endotoxin ranged within 16.9-172.1 µg/m3 (median 30.0 µg/m3), exceeding at all sampling sites the suggested OEL value of 0.2 µg/m3. In conclusion, flax farmers performing machine scutching of flax could be exposed to large concentrations of airborne microorganisms, dust and endotoxin, posing a risk of work-related respiratory disease.
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