Unveiling the menace of lampenflora to underground tourist environments

Abstract

Permanent artificial lighting systems in tourist underground environments promote the proliferation of photoautotrophic biofilms, commonly referred to as lampenflora, on damp rock and sediment surfaces. These green-colored biofilms play a key role in the alteration of native community biodiversity and the irreversible deterioration of colonized substrates. Comprehensive chemical or physical treatments to sustainably remove and control lampenflora are still lacking. This study employs an integrated approach to explore the biodiversity, eco-physiology and molecular composition of lampenflora from the Pertosa-Auletta Cave, in Italy. Reflectance analysis showed that photoautotrophic biofilms are able to absorb the totality of the visible spectrum, reflecting only the near-infrared light. This phenomenon results from the production of secondary pigments and the adaptability of these organisms to different metabolic regimes. The biofilm structure mainly comprises filamentous organisms intertwined with the underlying mineral layer, which promote structural alterations of the rock layer due to the biochemical attack of both prokaryotes (mostly represented by Brasilonema angustatum) and eukaryotes (Ephemerum spinulosum and Pseudostichococcus monallantoides), composing the community. Regardless of the corrosion processes, secondary CaCO₃ minerals are also found in the biological matrix, which are probably biologically mediated. These findings provide valuable information for the sustainable control of lampenflora.

Keywords: Biodeterioration; Geobiology; Pertosa-Auletta Cave; Photoautotrophic biofilms; Show caves.

Figure 1

Pertosa-Auletta Cave map; the yellow circles indicate the studied lampenflora samples along the tourist trail (green). The map was generated using the open-source vector graphics editor Inkscape 0.92 (www.inkscape.org).

Figure 2

Field image of the four sampling sites from Pertosa-Auletta Cave, with the respective lampenflora reflectance spectra: (a) L1; (b) L2; (c) L3; (d) L4.

Figure 3

FESEM images of the green biofilm samples from Pertosa-Auletta Cave. Filamentous microorganisms are shown in L1 (a), L4 (b), L3 (c), L2 (d), diatoms in L4 (e) and L1 (f); needle-fiber calcite structures in L2 and L3 (g and h, respectively), and biogenic-like mineral grains associated with filamentous microorganisms (i and j, respectively). The yellow arrows indicate the features mentioned in the text.

Figure 4

Representative optical microscopy images of the green biofilm samples from Pertosa-Auletta Cave: L1 (a), L2 (b), L3 (c), L4 (d).

Figure 5

Prokaryotes and Eukaryotes composition of the lampenflora for each sampling site. The barplots show the relative abundances (%) at phylum (a and d, respectively), class (b and e, respectively), and order levels (c and f, respectively).

Figure 6

Principal component analysis of the most abundant populations (> 5%) present in the lit tourist trail of the Pertosa-Auletta Cave, determined at the family level. Green light for sampling sites L1 and L4, and white light for sampling sites L2 and L3. The Simpson similarity index values are also present. (a) Bacterial populations; (b) Eukaryotic populations.