Background: Hopanoids modify plasma membrane properties in bacteria and are often compared to sterols that modulate membrane fluidity in eukaryotes. In some microorganisms, they can also allow adaptations to extreme environments. Methods: Hopanoids were identified by liquid chromatography–mass spectrometry in fourteen strains of thermophilic bacteria belonging to five genera, i.e., Alicyclobacillus, Brevibacillus, Geobacillus, Meiothermus, and Thermus. The bacteria were cultivated at temperatures from 42 to 70 °C. Results: Regardless of the source of origin, the strains have the same tendency to adapt the hopanoid content depending on the cultivation temperature. In the case of aminopentol, its content increases; aminotetrol does not show a significant change; and in the case of aminotriol the content decreases by almost a third. The content of bacteriohopanetetrol and bacteriohopanetetrol glycoside decreases with increasing temperature, while in the case of adenosylhopane the opposite trend was found. Conclusions: Changes in hopanoid content can be explained by increased biosynthesis, where adenosylhopane is the first intermediate in the biosynthesis of the hopanoid side chain.

Members of the genus Kocuria are often found in soils contaminated with toxic metals or exposed to high levels of ionizing radiation. The use of classical cultivation technics often leads to the isolation of Kocuria sp. from underground spring waters. These bacterial isolates have to adapt their metabolism to survive in such extreme environments. Four bacterial isolates of the genus Kocuria (Kocuria sp. 101, 208, 301, and 401) were obtained from radon spring water (Jachymov, Czech Republic). These isolates were tested for their ability to withstand stress and extreme conditions. Growth was observed at a temperature range of 10–45 °C with optimal growth temperature between 20 and 30 °C. The content of polyunsaturated fatty acids in all four isolates was proved to be temperature-dependent. The strain Kocuria sp. 301 showed high resistance to all studied extreme conditions (UV radiation, desiccation, and free radicals in medium). The results suggest that isolates from radioactive springs might have developed mechanisms that help them survive under several extreme conditions and could be used in biotechnological production.

Boswellic acids are biologically active pentacyclic terpenoid compounds derived from Boswellia sp. plants. Extracts containing these acids have a number of positive effects on human health, especially in the treatment of inflammation, arthritis, or asthma. With increasing resistance to common antibiotics, boswellic acid-containing extracts could serve as an alternative or work in synergy with commonly available preparations. This study aims to determine the effect of boswellic acids on suspension cells and biofilms of Staphylococcus epidermidis, Enterococcus faecalis, and Escherichia coli. The antimicrobial and antibiofilm effect found was compared with commonly available antibiotics to control these undesirable microorganisms. The synergistic effect of boswellic acids and common antibiotics on the growth of these microorganisms was also determined. All tested microorganisms showed a positive additive effect of antibiotics and boswellic acid extract. The most significant effect was found in Enterococcus faecalis ATCC 29212 in a combination of 0.2 × MIC80 erythromycin (0.2 mg/L) and 0.8 × MIC80 boswellic acid extract (16 mg/L).

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Resistance to adverse conditions is widespread in the microbial world. Microorganisms resistant to ionizing radiation form a technologically interesting but little-explored group. This work focuses on the mechanisms of resistance to radiation in representatives of the Actinobacteria phylum, both in terms of detoxification mechanisms and in terms of repairing DNA damage.