Update: Living Reticulated Filaments from Herbstlabyrinth-adventhöhle Cave System, Germany

Previous reports of reticulated filaments, an unknown microbe, document that they are ubiquitous in subsurface environments, including limestone caves, lava tubes, and even granite tunnels. Although initial reports of fossil reticulated filaments described preserved organic matter, additional instances involve replacement by calcite, Mn-oxides, silica, or copper silicates. We report on living reticulated filaments found in the limestone Herbstlabyrinth-Adventhöhle Cave System, Hesse, Germany. Samples from soft pool-fingers, pool-bottom clays, and clay-coated rocks along the flow path of incoming water all contain living reticulated filaments associated with abundant biofilm. Most of the reticulated filaments are approximately 0.5 mm in diameter, reach lengths between 150 and 200 mm, and have irregular chambers with spines, a newly identified morphological variant. EDX of these filaments confirms an organic composition not replaced by minerals. They are the dominant visible microbial form in these biofilms, providing hope that they can be isolated and identified.