Diverse microbial species survive high ammonia concentrations

Abstract

AbstractPlanetary protection regulations are in place to control the contamination of planets and moons with terrestrial micro-organisms in order to avoid jeopardizing future scientific investigations relating to the search for life. One environmental chemical factor of relevance in extraterrestrial environments, specifically in the moons of the outer solar system, is ammonia (NH3). Ammonia is known to be highly toxic to micro-organisms and may disrupt proton motive force, interfere with cellular redox reactions or cause an increase of cell pH. To test the survival potential of terrestrial micro-organisms exposed to such cold, ammonia-rich environments, and to judge whether current planetary protection regulations are sufficient, soil samples were exposed to concentrations of NH3from 5 to 35% (v/v) at −80°C and room temperature for periods up to 11 months. Following exposure to 35% NH3, diverse spore-forming taxa survived, including representatives of theFirmicutes(Bacillus, Sporosarcina, Viridibacillus, Paenibacillus, StaphylococcusandBrevibacillus) andActinobacteria(Streptomyces). Non-spore forming organisms also survived, includingProteobacteria(Pseudomonas) andActinobacteria(Arthrobacter) that are known to have environmentally resistant resting states.Clostridiumspp. were isolated from the exposed soil under anaerobic culture. High NH3was shown to cause a reduction in viability of spores over time, but spore morphology was not visibly altered. In addition to its implications for planetary protection, these data show that a large number of bacteria, potentially including spore-forming pathogens, but also environmentally resistant non-spore-formers, can survive high ammonia concentrations.