Actinobacteria belonging to the genus Rubrobacter are known for their multi-extremophilic growth conditions-they are highly radiation-resistant, halotolerant, thermotolerant or even thermophilic. This work demonstrates that the members of the genus are capable of accumulating polyhydroxyalkanoates (PHA) since PHA-related genes are widely distributed among Rubrobacter spp. whose complete genome sequences are available in public databases. Interestingly, all Rubrobacter strains possess both class I and class III synthases (PhaC). We have experimentally investigated the PHA accumulation in two thermophilic species, R. xylanophilus and R. spartanus. The PHA content in both strains reached up to 50% of the cell dry mass, both bacteria were able to accumulate PHA consisting of 3-hydroxybutyrate and 3-hydroxyvalerate monomeric units, none other monomers were incorporated into the polymer chain. The capability of PHA accumulation likely contributes to the multi-extremophilic characteristics since it is known that PHA substantially enhances the stress robustness of bacteria. Hence, PHA can be considered as extremolytes enabling adaptation to extreme conditions. Furthermore, due to the high PHA content in biomass, a wide range of utilizable substrates, Gram-stain positivity, and thermophilic features, the Rubrobacter species, in particular Rubrobacter xylanophilus, could be also interesting candidates for industrial production of PHA within the concept of Next-Generation Industrial Biotechnology.

Biology Centre The Czech Academy of Sciences v v i Branisovska 31 370 05 Ceske Budejovice Czech Republic

Department of Biomedical Engineering Faculty of Electrical Engineering and Communication Brno University of Technology Technicka 12 616 00 Brno Czech Republic

Department of Food Chemistry and Biotechnology Faculty of Chemistry Brno University of Technology Purkynova 118 612 00 Brno Czech Republic

Faculty of Science Charles University Vinicna 7 128 44 Prague 2 Czech Republic

Institute of Scientific Instruments of the Czech Academy of Sciences v v i Kralovopolska 147 612 64 Brno Czech Republic

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