Metagenomic Analysis of Microbial Communities Potentially Involved in the Deterioration of Archaeological Objects at the Roman Aqueduct of Gadara

Gadara aqueduct is a trans-regional Roman aqueduct system that begins at an ancient lake in Syria, runs for around 60 kilometers on the surface, and then disappears in Jordan. Its longest underground section is considered the longest known tunnel system of the ancient world. In this work, we focus on identifying the prokaryotic microorganisms existing in the atmosphere of the tunnel in addition to the soil of the vicinity of the tunnel. Therefore, a metagenomics approach was utilized to reveal the diversity of microorganisms existing. Additionally, a culture-dependent approach was utilized to isolate the dominant prokaryotic microorganisms. Different types of air and soil samples were taken from different locations along the Gadara tunnel (aqueduct) and at different times during the period from September 2015 to October, 2016. A total of 25 samples were collected. Sampling was carried out before and after the tunnel rehabilitation. Subsequently, a total of 269678 sequences were identified within the domains of Bacteria and Archaea. The bacterial phyla Proteobacteria, Actinobacteria, Fitmucutes and Bacteroidetes were generally the most abundant prokaryotic phyla in the studied samples. Moreover, Archaea was also present through the phylum Euryarchaeota and the genus Halobacterium. Several sequences were found to denote extremophilic microorganisms, namely, halophiles. The culture-dependent method revealed lower microbial diversity because all cultivated strains were Gram-positive bacilli and belong mainly to genus Bacillus.