The lampenflora disease in show caves: testing the efficacy of the most used methods to control microbial growth

The development of complex photosynthetic communities in underground environments equipped with artificial lighting, the so-called lampenflora, represents a serious problem for show caves. In particular, the proliferation of biofilms composed by photosynthetic microorganisms causes aesthetical, physical and chemical changes on the colonized rock substrates. Understanding its physiology and the efficacy of the most used methods for controlling lampenflora is now an urgency for a sustainable management of tourism in caves. Reflectance analysis on lampenflora from Pertosa-Auletta limestone Cave (Italy) revealed its capacity to absorb all frequencies of visible light, reflecting only the near-infrared, probably due to the production of secondary accessory pigments and to the mixotrophic metabolic regimes. The biofilm matrix is mainly composed of filamentous organisms tangled with mineral grains. This biofilm promotes rock corrosion processes, as well as the precipitation of secondary minerals. When testing the most used lampenflora removal techniques in Pertosa-Auletta Cave, NaClO (bleaching agent) exhibited long-term efficacy in disinfecting the colonized surfaces. Conversely, the surfaces treated with H2O2 (oxidizing agent) showed a rapid recovery of the biofilms after three months from the treatment. Yet, both chemical treatments were efficient on the elimination of photoautotrophs, but ineffective against the bacterial phyla Proteobacteria and Bacteroidetes, and Apicomplexa and Cercozoa among the Eukaryotes. UVC lighting showed no biofilm alterations with the protocols used in the experimental plan of this research.