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Microorganisms
Volume 14
Issue 2
10.3390/microorganisms14020368
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Article

Evaluation of the Bacterial Diversity in the World’s Deepest Cave—Veryovkina, Arabika Massif, Western Caucasus

by
Yordan Hodzhev
1,*,
Violeta Zhelyazkova
2,
Nia Toshkova
2,
Anna S. Barashkova
3,4,
Borislava Tsafarova
5,6,
Stefan Panaiotov
5,6,* and
Pavel Stoev
2
1
Department of Natural Sciences, New Bulgarian University, 1618 Sofia, Bulgaria
2
National Museum of Natural History, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria
3
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences (RAS), ul. Miklukho-Maklaya, 16/10, 117997 Moscow, Russia
4
All-Russian Institute of Plant Protection, 196608 Saint Petersburg, Russia
5
National Center of Infectious and Parasitic Diseases, 1504 Sofia, Bulgaria
6
Center of Competence “Immunopathogen”, Y. Sakazov 26, 1504 Sofia, Bulgaria
*
Authors to whom correspondence should be addressed.
Microorganisms 2026, 14(2), 368; https://doi.org/10.3390/microorganisms14020368
Submission received: 16 November 2025 / Revised: 26 December 2025 / Accepted: 30 January 2026 / Published: 4 February 2026
(This article belongs to the Special Issue Microorganisms in Extreme Environments)
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Abstract

Veryovkina Cave is the world’s deepest known cave (2212 m deep). It is located in the Arabika Massif of Gagra Mountain in the Western Caucasus. Its microbiome remains unknown because of difficulties in access. Ten sediment samples were collected at vertical depths ranging from 300 m to 2204 m; they varied by substrate type, moisture content, and visitor accessibility. Total microbial DNA was isolated, and 16S ribosomal gene metabarcoding was applied for taxonomic identification. Seven samples showed reliable content, whereas three samples indicated no recoverable reads. Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant phyla in total. Depth stratification of microbiota showed that (1) shallow wet clays were dominated by Acidimicrobia and Actinobacteria; (2) mid-depth wet clays showed the highest abundance of Nitrospira, Betaproteobacteria, and Vicinamibacter; and (3) deep, dry substrates were dominated by Thermoleophilia and Rubrobacteria. Multivariate analyses showed that substrate type and moisture tended to explain more variation in microbial abundance than depth or human activity. We demonstrate the presence of distinct ecological niches within the cave ecosystem, which emphasizes the role of local conditions in shaping microbial diversity.
Keywords: cave microbiota; Veryovkina Cave; 16S rRNA amplicon sequencing cave microbiota; Veryovkina Cave; 16S rRNA amplicon sequencing

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MDPI and ACS Style

Hodzhev, Y.; Zhelyazkova, V.; Toshkova, N.; Barashkova, A.S.; Tsafarova, B.; Panaiotov, S.; Stoev, P. Evaluation of the Bacterial Diversity in the World’s Deepest Cave—Veryovkina, Arabika Massif, Western Caucasus. Microorganisms 2026, 14, 368. https://doi.org/10.3390/microorganisms14020368

AMA Style

Hodzhev Y, Zhelyazkova V, Toshkova N, Barashkova AS, Tsafarova B, Panaiotov S, Stoev P. Evaluation of the Bacterial Diversity in the World’s Deepest Cave—Veryovkina, Arabika Massif, Western Caucasus. Microorganisms. 2026; 14(2):368. https://doi.org/10.3390/microorganisms14020368

Chicago/Turabian Style

Hodzhev, Yordan, Violeta Zhelyazkova, Nia Toshkova, Anna S. Barashkova, Borislava Tsafarova, Stefan Panaiotov, and Pavel Stoev. 2026. "Evaluation of the Bacterial Diversity in the World’s Deepest Cave—Veryovkina, Arabika Massif, Western Caucasus" Microorganisms 14, no. 2: 368. https://doi.org/10.3390/microorganisms14020368

APA Style

Hodzhev, Y., Zhelyazkova, V., Toshkova, N., Barashkova, A. S., Tsafarova, B., Panaiotov, S., & Stoev, P. (2026). Evaluation of the Bacterial Diversity in the World’s Deepest Cave—Veryovkina, Arabika Massif, Western Caucasus. Microorganisms, 14(2), 368. https://doi.org/10.3390/microorganisms14020368

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