Polyhydroxyalkanoates (PHA) are microbial storage polyesters that represent a renewable and environmentally friendly alternative to petrochemical plastics. However, their production and use are severely disadvantaged by the high production cost. The use of extremophilic PHA producers is one of the ways to reduce the cost of PHA production. Extremophiles bring numerous advantages resulting from the high robustness of the process against microbial contamination. In this doctoral thesis, attention was focused on the study of PHA production using selected halophilic and thermophilic microorganisms. Representatives of the genus Halomonas were mainly from public collections of microorganisms. Two promising PHA producers on waste frying oil were identified, namely Halomonas hydrothermalis and Halomonas neptunia. Both strains achieved good PHA yields in flask experiments. With the addition of suitable structural precursors, they were also able to produce copolymers with interesting material properties. However, in the proposed thesis, the main emphasis was placed on the study of PHA production using thermophilic microorganisms. As a part of the work, the isolation of thermophilic PHA producers from various thermophilic consortia (active sludge, compost, etc.) was performed. During isolations experiments, an original isolation procedure was designed using changes in osmotic pressure, the so-called osmoselection. Dozens of promising thermophilic PHA producers were obtained thanks to this original approach. They were taxonomically classified using 16S rRNA and tested for production potential. The most promising PHA producer was the isolate which was classified as Aneurinibacillus sp. H1. This bacterium is able to utilize a variety of substrates, including waste glycerol, to produce PHA. Even more important is the capability of synthesizing copolymers with a high content of 4-hydroxybutyrate. The monomer composition of the PHA copolymer and thus the material properties of the prepared copolymer can be controlled by suitable adjustment of the cultivation conditions. The prepared copolymer P(3HB-co-4HB) has unique properties and the great application potential in numerous high-end applications, for example in the field of health care, food industry or cosmetics.

This thesis deals with the study of polyhydroxyalkanoate biosynthesis as a microbial product with the potential to replace current conventional plastics made from petroleum. The dissertation thesis is elaborated in the form of a discussed set of already published publications, which are then part of the thesis in the form of appendices. The work builds on relatively extensive knowledge in the field of polyhydroxyalkanoate production and brings new facts and possible strategies. Various possibilities of analysis of polyhydroxyalkanoates using modern methods were tested in this work, which brings especially speed, which can be crucial in real-time evaluation of production biotechnological process. Raman spectroscopy has proven to be a very promising technique for rapid quantification of PHA. Furthermore, the work deals with valorisation of waste of food and agricultural origin. Emphasis is placed on methods of detoxification of lignocellulose hydrolysates. In this context, adsorption of inhibitors to lignin was first used as an alternative to other detoxification techniques. Due to detoxification, selected production strains Burkholederia cepacia and B. sacchari were able to utilize softwood hydrolyzate for PHA production. In the next part of the work was also tested the possibility of using chicken feathers as a complex source of nitrogen. Evolutionary engineering was also used as a possible strategy to eliminate the inhibitory effect of levulic acid as a microbial inhibitor that results from the hydrolysis of lignocellulosic materials. Adaptation experiments were used to develop strains exhibiting higher resistance to levulic acid and the ability to accumulate a higher 3HV copolymer from the original wild-type C. necator strain. Another promising approach tested in the work was the use of extremophilic microbial strain, which leads to a reduction in the cost of biotechnological production. Selected Halomonas species have shown high potential as halophilic PHA producers. The final part of the thesis was devoted to the selection of the production strain with regard to the properties of the resulting PHA. The Cupriavidus malaysiensis strain was selected to produce a P(3HB-co-3HV-co-4HB) terpolymer which revealed significant differences in material properties over P3HB.