Effect of Cultivation Conditions on the Expression of the Exiguobacterium sibiricum Proteorhodopsin Gene

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Lada E. Petrovskaya^1,2,a*, Elena V. Spirina³, Artemiy Yu. Sukhanov⁴, Elena A. Kryukova¹, Evgeniy P. Lukashev⁵, Rustam H. Ziganshin¹, Elizaveta M. Rivkina³, Dmitrii A. Dolgikh^1,5, and Mikhail P. Kirpichnikov^1,5

¹Shemyakin–Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia

²Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Moscow Region, Russia

³Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia

⁴FRC Kazan Scientific Center, Russian Academy of Sciences, 420111 Kazan, Russia

⁵Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

^* To whom correspondence should be addressed.

Received: March 28, 2025; Revised: May 25, 2025; Accepted: May 28, 2025

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Recombinant proteorhodopsin ESR of the gram-positive bacterium Exiguobacterium sibiricum isolated from permafrost deposits in northeastern Siberia binds retinal and acts as a light-dependent proton pump, but not much is known about its expression under natural conditions. In this work, expression of the esr gene in E. sibiricum cultures grown under various conditions was studied by quantitative PCR. It has been discovered that cultivation on poor media at low temperatures contributes to a significant increase in the content of the corresponding mRNA. The data obtained are confirmed by the results of the analysis of the membrane fraction of cells using label-free quantitative chromatography-mass spectrometry. Also, at 10°C, increased content of phytoene desaturases, which are involved in the biosynthesis of carotenoids, is observed. However, we were unable to detect the presence of a functional retinal-containing protein in the cells, presumably due to the lack of an enzymatic retinal synthesis system in E. sibiricum. The possible functions of ESR in E. sibiricum cells are discussed in connection with the characteristics of the extreme habitat of the bacterium. The results of this study contribute to expanding the understanding of the molecular mechanisms of microbial adaptation to environmental conditions and the potential role of microbial rhodopsins in these processes.

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KEY WORDS: Exiguobacterium sibiricum, permafrost deposits, microbial rhodopsins, retinal, carotenoids

DOI: 10.1134/S0006297925600917

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