Introduction: Many scientists and other interested groups are trying for years to discover "harmless" or degradable plastics to prevent excessive accumulation of plastics in the environment. Purpose: The purpose of the Master's thesis is to determine the presence and number of groups of microorganisms during the processing of plastics into various products at the observed manufacturers, and to identify these microorganisms. We also wanted to check the bacterial strains' ability to degrade polystyrene (PS) plastic mass. Methods: In the processing industry of plastic products, we took samples for microbiological tests at various stages of processing on the surfaces of the production line and finished products using swabs and the contact method. The presence and number of microorganisms on raw materials and finished products was determined by washings. In the first part of the master's thesis, we isolated individual bacteria and fungi from the samples and identified them using biochemical and spectrophotometric (MALDI-TOF) methods. In the second part, we observed the ability to degrade the polymer by determining the transparent zone of degradation of PS powder in the culture medium around grown colonies of selected bacterial strains and by measuring the loss of mass of PS in the bacterial culture after one and two months of incubation. The presence of biofilms and the potential viability of bacteria on PS tiles were observed by SEM and fluorescence microscopy. Results: We did not find major differences in the number and type of microorganisms between the three manufacturers and production lines. There were also no differences in the number of microorganisms between the individual sample sites of the production lines. We mostly isolated Gram-positive bacteria. Out of 109 samples, we identified 39 % of bacteria from the genera Bacillus, 34 % Staphylococcus and 10 % each from the genera Micrococcus, Burkholderia and Moraxella. A transparent zone of degraded PS around the colonies on the culture medium was obtained in 3 strains of the Bacillus licheniformis species, and colony growth was also observed in 64 strains, which means that the bacteria nevertheless used the polymer as a carbon source. The loss of PS mass under the influence of the decomposition of the selected strains was from 1.5 to 8 % at the incubation temperature of 37 °C and from 2.1 to 14.4 % at the incubation temperature of 55 °C. Here too, the most active strains were Bacillus and Micrococcus. The concentration of bacterial cells or the intensity of their reproduction in the culture medium was not positively correlated with their decomposition and the reduction of the mass of the PS polymer. When observing the PS grains under a scanning electron microscope (SEM), we obtained images showing the biofilm or cells attached to the PS grains. The cells were most often attached to the rough surface. Some strains showed respiratory activity under a fluorescence microscope even after 60 days of incubation in MSM without a carbon source on PS plates. Discussion and conclusion: Different bacteria can also be present in the production of plastic products, which are able to survive on the surfaces of PS plastic mass and also degrade it. These are mainly strains of Staphylococcus, Bacillus, Micrococcus, which are also common in the environment. Due to the large consumption of plastic products, with which we are greatly burden the environment, many studies are looking for new biological approaches for its decomposition. This include microorganisms, genetic engineering, enzyme action, etc. Trends for the production of biodegradable plastics, which are less harmful to the environment, are also in the foreground.
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