Underground environments are inhospitable habitats for microbial life. However, many studies have unearthed a diverse variety of microbial life in underground environments. The microbial communities of underground environments in the UK have been little studied. Here, we examine the microbial life of biofilms, including snottites, from six cave and mine sough sites in northern England. Microorganisms living in underground environments must protect themselves from the extreme conditions encountered there and may form biofilms as one method of protection. One specialised type of biofilm is known as a snottite. These are jelly-like, pendulous biofilms which hang from the roof of caves and mines. Snottites are often found in hypogenic sulphur-acid caves and acid mine environments, where they are described as being extremely acidic (pH 0-2). Samples of water, rock, sediment and speleothem were collected and analysed to determine the geochemical influences on microbial life. Biofilm samples were collected and analysed using culture-dependant and culture-independent methods, and the metabolic pathways of the resulting metagenomic sequences were examined. Using these, we create suggested metabolic cycles for each site, showing how bacteria might be utilising elements from the environment and potential interactions between bacterial species. We show that each underground site contains micro-environments, each of which harbours its own distinct microbial population. The elemental influences in these micro-environments can vary considerably across small distances. A variety of bacterial strains were identified and were compared to bacteria found in studies of bacterial communities from similar sites in the literature. Unlike previously described extremely acidic snottites, biofilms from the mine soughs we studied, including snottites, are neutral or weakly acidic (pH 4-7). This is due to the influence of calcium carbonate buffering the internal acidity of the snottites. Despite their differing pH, the snottites we studied shared several of the same species of bacteria and metabolic processes with their more acidic counterparts. We hypothesise from these discoveries that the energy source of an environment has more influence over the microbial population than the pH. We have used these findings to propose three models of snottite formation for snottites found in hypogenic caves, acid mine environments, and neutral mine environments. We also found evidence of other organisms, including mites, living in snottites, and thus consider the role of bacteria as the base of snottite ecosystems
