The pathogenic potential of old guano deposits – 16S rRNA gene-based metabarcoding in Muierilor Cave, South-Western Carpathians. undefined

Muierilor Cave is one of the most important show caves in Romania, with paleontological and archaeological deposits. A new chamber was discovered recently in the cave, with unique yellow calcite crystals, fine crusts and black sediments. The deposits in this chamber were related to a leaking process from the upper level that contains fossil bones and a large deposit of guano. Samples were taken from the new chamber and another passage to investigate the diversity of microorganisms in relation to the substrates and to potentially identify the taxa that are pathogenic for humans, animals or plants. Chemical, mineralogical and whole community 16S rRNA gene-based metabarcoding analysis were undertaken and the base of the guano deposit was radiocarbon dated to 1,315 ± 30 years BP. Metabarcoding of the analyzed samples found that ~0.7% of the identified bacteria are not known to science, and ~16% of the identified bacteria are pathogenic for humans. More than 87% of pathogenic and non-pathogenic bacteria genera not previously reported in caves or guano were also found, which may sustain the long-term impact humans and animals have in their transmission. Bacteria with a pathogenic potential can originate from the surface or the organic deposits inside the cave, such as the bats guano. The identified human pathogenic genera were Streptococcus, Enterobacter, Campylobacter, Clostridium, or Pseudomonas with well-known human pathogenic species. Our study indicates guano and bats as an important source of microorganisms potentially pathogenic even for hundreds of years, and in areas which apparently are far from both bats and guano deposits. Continuous monitoring of air and floor microbiology should be considered in show caves with guano deposits, especially in the actual context with intense inter-continental tourism and increased threats of global pandemics.