Biological activity of Pseudomonas sp. В-6798 bacteria in batch and chemostat culture

The usage of chemical plant protection substances against pests and pathogenicagents has been increasing lately in agriculture, which results in the deterioration of theenvironmental situation in agrophytocenoses. The biological method is viewed as an alternativeone in the system of protective measures and at the same time, due to its specificfeatures, is the basis for elaborating ecologically safe, economical and long-runprograms for fighting harmful organisms.Pseudomonas sp. В-6798 bacteria, presented as a biopreparation agent, give a significantpositive effect while inoculating a variety of agricultural plants. The possibilityof the bacteria to use formaldehyde in the composition of nutrient solutions as a singlesource of energy substrate, that is at the same time a growth inhibitor of a significantquantity of other organisms, allows carrying out cultivation in the regime of unprotectedfermentation, and, therefore, it is easily fulfilled in the chemostat.The aim of this work was to study biological activity of Pseudomonas sp. В-6798 inbatch and chemostat culture.The cultivation of bacteria was carried out in a standard laboratory fermenter(V=200 ml) on a mineral medium with formaldehyde with the concentration of 2 g/L as asingle source of carbon and energy. The volume of inoculum amounted to 10% of thebioreactor working volume; the concentration of dissolved oxygen was kept at the levelof 70-75%. In the regime of unprotected batch cultivation bacteria were grown up totheir achieving the abundance of 6,8.108 cells/ml. Despite the fact that the stock culturewas homogeneous and consisted of morphologically identical cells, after batch cultivationin the fermenter, without following aseptic rules, we identified six morphologicallydifferent types of colonies and classified them as different isolates. Further, the bacterialculture under investigation was put into the chemostat (D=0,003 p-1). After a week theculture was stabilized at the dilution rate with the abundance 6,5.104 cells/ml. While inoculatingsolid medium, the presence of strain dissociation and the presence of extraneousmicroflora were not found; new colonies were morphologically identical to the coloniesof the stock strain.During the cultivation, antifungul and growth stimulating activities of Pseudomonassp. В-6798 bacteria were estimated on wheat seeds in batch and continuous culture. It isestablished that biological activity of Pseudomonas sp. В-6798 bacteria depends on thecultivation regime: continuous cultivation increases biological activity of the producerstrainby contrast to batch one. During seed bacterization with the culture grown inbatch cultivation, the efficiency of seed infection suppression made up 14-16,5%,whereas during bacterization with the chemostat culture it was 24-27%. The bacteriagrown in batch fermentation fostered an increase in wheat seedlings length twice, whilethe bacteria from the chemostat increased the seedling length six times in comparisonwith seeds without bacterization.

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