The Geomunoreum Lava Tube System, declared as a UNESCO World Heritage Site, has a unique natural ecosystem. The information available about this ecosystem, which contains lava caves with secondary carbonate speleothems, is sparse. Hence, extensive research is warranted for establishing a conservation standard. We commenced microbial research on the system and have been studying the microorganisms coating the lava tube wall to acquire fundamental information for understanding the lava cave ecology of Jeju Island. Samples were collected from yellow-colored walls in six caves that are part of the system―the Bengdwi, Utsanjeon, Bukoreum, Manjang, Gimnyeong, and Yongcheon caves. This study focused on yellow walls as it is the most easily distinguished color. According to previous studies, the color of cave walls is attributed to microorganisms or their components. To determine whether the yellow mats from the Jeju lava tube walls are caused by microorganisms, we examined samples at the microscopic scale, by staining mats and analyzing bacterial isolates from glitter particles. As a result, we found that the yellow walls of lava tubes are comprised of microbial mats.

To isolate and identify the yeast strains associated with D. morbifera, homogenized D. morbifera root samples were spread onto GPY, DG18, SCG and DOB agar media containing antibiotics, Triton X-100, and l-sorbose. Total 81 yeast isolates were analyzed by sequencing of internal transcribed spacer (ITS) region of the ribosomal DNA. The results showed that the root-associated yeast species were composed of the genera Vanderwaltozyma (40 isolates), Cryptococcus (40 isolates), and Kluyveromyces (one isolate). Moreover, the Kluyveromyces isolate exhibited high bioethanol productivity. In addition, the Vanderwaltozyma and Cryptococcus were dominant in D. morbifera roots. The specific yeast community associated with D. morbifera roots was identified by phylogenetic sequence analyses. These yeast isolates may have industrial applications as biosurfactant and bioethanol.