# Biological Control of Phototrophic Biofilms in a Show Cave: The Case of Nerja Cave
## 3 Results  
Table 1 indicates that the microbial communities of the samples taken from the speleothems coated by phototrophic biofilms collected in Nerja Cave were almost entirely composed of members of _Bacteria_, with percentages ranging between 100.0% and 99.7%. The _Archaea_ were practically non-existent, reaching 0.2% in sample 1A and 0.3% in sample 1C. The percentage of unassigned community members was zero. The phototrophic communities of Nerja Cave were composed of 12 phyla with percentages greater than 1% (Figure 2). The most abundant phyla were _Firmicutes, Proteobacteria_ and _Cyanobacteria_. Members of the phylum _Cyanobacteria_ contribute to the green color of biofilms, due to the chlorophyll and its photosynthetic function, while other phyla are mainly composed of heterotrophic bacteria. _Firmicutes_ was widely represented in sample 1 and _Proteobacteria_ in sample 2. _Cyanobacteria_ were abundant in samples 1A, 2A and 2C, which corresponded to the areas of epilithic phototrophic biofilms. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Kingdom** & **1A** & **1B** & **1C** & **2A** & **2B** & **2C** \\ \hline _Bacteria_ & 99.8 & 100.0 & 99.7 & 100.0 & 100.0 & 100.0 \\ _Archaea_ & 0.2 & 0.00 & 0.3 & 0.0 & 0.0 & 0.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Kingdoms distribution in phototrophic biofilms from Nerja Cave. Figure 2: Heat-map analysis of Nerja Cave biofilms. Taxonomic identifications of _Bacteria_ at phylum level. The phyla are described in the right column and their respective abundances included in the boxes. In a range of lower abundance were the phyla '_Candidatus_ Dadabacteria', which only reached significant representation in sample 1C, and _Actinobacteria_, in samples 1A, 2B and 2C. They were followed in abundance by the phylum _Chloroflexi_ in sample 2B and _Rhodothermaeta_ in sample 1A. The phylum _Bacteroidetes_ was relatively well represented in samples 1B and 2B. _Planctomycetes_ reached significant percentages in samples 2B and 2C, followed by _Balneolaeta_ in samples 1B and 1C. Finally, the superphylum _Patescibacteria_ reached percentages higher than 1% in samples 2A and 2B. The _Gemmatimonatedetes_ phylum was represented in sample 2 with percentages \(\leq\)1%. Figures 3 and 4 illustrate the bacterial diversity at the class and order levels. The communities of the two speleothems showed a high heterogeneity in abundance, depending on the location area (biofilm, without biofilm, and interface area), with high percentages in the classes _Bacilii_ and _Cyanophyceae_ (Figure 3). Considering all the six samples, the most abundant classes (those that at least reached a value greater than 5% in a sample) were _Bacilii_, _Cyanophyceae_, _Alphaproteobacteria_, _Gammaproteobacteria_, _Dadabacteria_, _Actinobacteria_, _Thermomicobia_, _Rhodothermia_ and _Cytophagia_. The phylum _Firmicutes_ and the class _Bacilii_ was one of the most abundant in samples 1 and 2. The order _Bacillus_ comprised two genera: _Bacillus_ and _Psychroacillus_. The genus _Bacillus_ was the most abundant in sample 1, while in sample 2 the abundance of _Bacillus_ fell between six and three times, with respect to sample 1. Figure 3: Heat-map analysis of Nerja Cave biofilms. Taxonomic identifications of _Bacteria_ at class level. The classes are described in the right column and their respective abundances included in the boxes. _Cyanobacteria_, the phylum that contained the phototrophic microorganisms, only included two identified genera: _Desertifulum_ and _Spirulina_ (Figure 5). In sample 1A, _Spirulinales_ showed a remarkable abundance, and decreased in samples 1B and 1C (Figure 4). High abundances of uncultured members of the class _Cyanophyceaeae_ were detected in samples 2A and 2C (Figure 5). It was interesting to find an abundance of _Spirulina_ in sample 1 and a total absence in sample 2. However, a high abundance of uncultured members of the class _Cyanophyceaeae_ was detected in sample 2, but lacking in sample 1.