Fig 1.
Location and plan-view maps of Fetida Cave A) Geographical location of Fetida Cave in Santa Cesarea Terme, Salento (SE Italy) and the cave map view from above. The cave opens along the Adriatic coastline following a NW-SE direction. B) Cross-section of Fetida Cave. In both A) and B), the sampling points are indicated as yellow points along the cave map. The yellow star (highlighted by an arrow in the cross-section) shows the position of the upwelling H2S-rich fluids.
Fig 2.
Field pictures of the most representative biofilms and deposits observed in Fetida Cave.
A) Water filaments attached to the rock in the cave stream close to the entrance (named F-stream samples); B) Water filaments floating in the water in the inner zone of the cave (named F-float samples); C) Water biofilms sedimented on the water stream bed in the inner zone of the cave (named F-sed samples); D) Gypsum moonmilk deposits on the cave walls and ceilings (named M samples). It is surrounded by hard whitish gypsum crusts; E-F) Grey (named V-grey samples) and brown (named V-brown samples) vermiculations covering the cave walls and ceiling.
Table 1.
Physico-chemical parameters of waters and air sampled at the entrance and in the inner zone of Fetida Cave and along the coastlinea,b.
Table 2.
Physico-chemical properties and composition of the Fetida Cave biofilms and deposits.
Table 3.
Chemical elements in the biodeposits from Fetida Cavea.
Fig 3.
FESEM images of the biodeposits collected in Fetida Cave.
A) Elongated filaments and particles characterized by sulfur crystals in F-stream samples; B) EDS spectrum of a sulfur crystal surrounded by filaments; C) F-sed collected from the water stream bed inside the cave. They appear more corroded than F-stream collected at the cave entrance; D) Gypsum microcrystals of moonmilk; E) V-brown is composed of a filamentous network, amorphous matrix and minerals. Minerals can be totally surrounded by filaments (see white arrow), which is probably the result of trapping and binding processes occurring in vermiculations; F) Prosthecate bacterium in grey vermiculation deposits.
Fig 4.
Diversity indices of the different biofilms from Fetida Cave.
The three different box plots include the data corresponding to all the samples representing each biofilm/deposit. Water filament samples are reported in red, vermiculation samples are shown in blue, moonmilk deposit samples are grey.
Fig 5.
Clustering of the different biofilm samples from Fetida Cave Cluster.
A) Clustering calculated using the Bray-Curtis distance between samples based on SV taxonomy classification in SILVA. B) Non-metric multidimensional scaling (nMDS) showing correlation between physico-chemical factors and biofilm microbial community composition. Water filaments are represented in red, vermiculations in blue, and moonmilk deposits in grey.
Fig 6.
Microbial community composition at phylum/proteobacteria class level of Fetida Cave samples representing water filaments, vermiculations and moonmilk deposits.
Microbial phyla and proteobacterial classes with abundance <1% are included in “Others” (S1 File).
Fig 7.
Heatmap showing the abundance of the microbial orders present in Fetida Cave samples.
Only orders with abundance >2% in at least one sample are reported. The higher taxonomy affiliation of the orders is reported on the right side of the figure.
Fig 8.
Heatmap showing the abundance of the microbial families present in Fetida Cave water filaments.
Only those families with a relative abundance >2% are shown.
Fig 9.
Phylogenetic tree of the most abundant SVs within water filaments/biofilms from Fetida Cave.
For taxonomy details and Best Blast Hit of the SVs reported, see S6 Table.
Fig 10.
Heatmap showing the abundance of the microbial families present in Fetida Cave vermiculations.
Only those families with a relative abundance >2% are shown.
Fig 11.
Phylogenetic tree of the most abundant SVs in V-grey (colored in grey) and V-brown (colored in brown) samples.
For taxonomy details and Best Blast Hit of the SVs reported, see S7 Table.
Fig 12.
Heatmap showing the abundance of the microbial families present in Fetida Cave moonmilk deposits.
Only those families with a relative abundance >2% are shown.
Fig 13.
Phylogenetic tree of the most abundant SVs in gypsum moonmilk in Fetida Cave.
For taxonomy details and Best Blast Hit of the SVs reported, see S8 Table.
Fig 14.
Schematic representation of the distribution pattern of water filaments, (bio)vermiculations and gypsum moonmilk in Fetida Cave, along with the most representative microbial groups (in white) and the main geochemical (within squares) and mineralogical (within ovals) characteristics in each type of biofilm/deposit.
The pH values are also reported. For the water filaments, the three filament morphologies are shown, i.e. floating, sedimented, and streamer filaments.