“…This aspect, alongside the higher percentage abundance of unclassi ed bacterial species in the east wall (16%) versus the west one (3%), might be ascribed to the far more proximity of the former to the external cave environment, easily allowing microbial colonization to occur in this area. Another contributing factor could derive from the high chlorine extent found in the east area of the cave, explaining its high microbial heterogeneity in terms of bacterial families such as Paenibacillaceae, Streptococcaceae, It is also worth noting that some of these bacterial families (i.e., Streptococcaceae, Ruminococcaceae, Moraxellaceae, Streptococcaceae, Oxalobacteriaceae, Eubacteriaceae, Sphingomonadaceae, to name a few) are ascribed to the gut microbiota of wildlife (e.g., bat) (Sun et al 2020;Gaona et al 2019) that could occasionally use the cave as a shelter, considering that the site entrance is not protected, thus contributing to the microbiota heterogeneity, as well as constituting a potential risk of cave damaging. Thus, microorganisms that can colonize such an environment are likely to be considered as both indigenous and foreign species, which however possess a versatile metabolism, allowing them to thrive under the most disparate nutritional conditions.…”