Seasonal diversity of the bacterial communities associated with petroglyphs sites from the Negev Desert, Israel

Rock art sites in the form of petroglyphs are found in the Negev Desert in southern Israel. These petroglyph sites include thousands of images depicting the life and culture of people in the region over the years. As they are part of the desert environment, these petroglyphs are exposed to natural and anthropogenic weathering processes. In natural rock sites, it is known that climatic conditions influence weathering and biofilm community development (Friedmann in Orig Life 10:223-235, 1980; Li et al. in PloS one 11:(9),163-287, 2016) Therefore, in order to develop tools for preservation and remediation, it is imperative to ascertain possible seasonal diversity of surface-inhabiting bacterial communities. To do so, we undertook to study and characterize the microbial communities inhabiting the rock sites during winter and summer. Next-generation sequencing (NGS) technologies using 16S rRNA gene were implemented on rock-surface slab samples to identify the microbial communities. 16S rRNA gene sequencing data revealed the presence of five main bacterial phyla, among them Actinobacteria, Cyanobacteria, Proteobacteria, Bacteroidetes, and Chloroflexi across the analyzed sites. The predominant phylum was Cyanobacteria (10-60% relative abundance), followed by Actinobacteria (20-60% relative abundance), Proteobacteria (5-35%), Bacteroidetes (0.02-35%), and Chloroflexi (1-12%). There was no significant difference in the bacterial diversity between samples from winter and summer. Five main phyla were observed in samples from the two seasons, winter (December) 2017 and summer (July) 2018. This study provides an important first step in understanding the possible seasonal dynamic of bacterial communities associated with the petroglyphs.