Phylogenetic tree of bacterial rDNA clones derived from Llonín and La Garma Caves (this study) and from Tito Bustillo and Altamira Caves [28,29] showing their relationship to members of the Proteobacteria and Nitrospira group. Partially sequenced clones (200 bp) are not shown in the tree (18 clones of the Proteobacteria, two clones of the Nitrospira group). An alignment of 488 bp was used for constructing the tree. Thermoproteus was used as the outgroup. Accession numbers are given in parentheses. The scale bar represents 0.1 substitutions per base position.