Phylogenetic diversity of bacteria associated with Paleolithic paintings and surrounding rock walls in two Spanish caves (Llonín and La Garma)

Abstract

Bacterial diversity in caves is still rarely investigated using culture-independent techniques. In the present study, bacterial communities on Paleolithic paintings and surrounding rock walls in two Spanish caves (Llonín and La Garma) were analyzed, using 16S rDNA-based denaturing gradient gel electrophoresis community fingerprinting and phylogenetic analyses without prior cultivation. Results revealed complex bacterial communities consisting of a high number of novel 16S rDNA sequence types and indicated a high biodiversity of lithotrophic and heterotrophic bacteria. Identified bacteria were related to already cultured bacteria (39 clones) and to environmental 16S rDNA clones (46 clones). The nearest phylogenetic relatives were members of the Proteobacteria (41.1%), of the Acidobacterium division (16.5%), Actinobacteria (20%), Firmicutes (10.6%), of the Cytophaga/Flexibacter/Bacteroides division (5.9%), Nitrospira group (3.5%), green non-sulfur bacteria (1.2%), and candidate WS3 division (1.2%). Thirteen of these clones were most closely related to those obtained from the previous studies on Tito Bustillo Cave. The comparison of the present data with the data obtained previously from Altamira and Tito Bustillo Caves revealed similarities in the bacterial community components, especially in the high abundance of the Acidobacteria and Rhizobiaceae, and in the presence of bacteria related to ammonia and sulfur oxidizers.