Stress resistance of bacterial pure cultures and mixed cultures

The purpose of this bachelor thesis was to investigate a stress resistance of bacterial monocultures and defined mixed culture. The theoretical part contains a literary review, which deals with the general stress resistance of bacteria and the dynamics of their growth. Furthermore, polyhydroxyalkanoates are introduced, as well as their involvement into stress response of bacteria. In this review was also elaborated the flow cytometry, significant modern method, which was important part of the experiment. In the experimental part, the resistance to osmotic and temperature stress was studied. For this purpose, monocultures of the PHA accumulating strain Cupriavidus necator H16 and the mutant strain Cupriavidus necator H16/PHB-4 unable to accumulate PHA were used. The defined mixed culture was prepared by cocultivating these two strains. Overall, the accumulation and utilization of PHA, namely poly (3-hydroxybutyrate), increased the resistance of bacteria. The most notable was the increase in the case of osmotic stress, when salt concentrations did not significantly reduce the viability of Cupriavidus necator H16 against a mutant strain which viability decreased with growing intensity of stress. On the other hand, experimental temperatures did not have a significant effect on cell viability. The highest growth of bacteria was recorded, in most cases, at their temperature´s optimum of 30 °C