Risk assessment of change in respiratory gas concentrations by native culturable bacteria in the air of sulfide ore mines

Sulfide ores are extracted from mines at considerable depths, that having unique a physical and chemical environment. On the one hand, physical, chemical, and biological processes taken place in the rocks produce this environment; on the other hand, they form unique bacterial communities. The aim of this study was to study the native culturable aerobic bacteria present in the sulfide ores of the deposits located in the Krasnoyarsk Territory (Russia) and evaluate their activity in relation to respiratory gases (oxygen and carbon dioxide) present in air. The results of the study established that the culturable bacteria present in the sulfide ore of the N1 deposit were related to genera Bacillus and Paenibacillus (class Bacilli), genera Citricoccus, Micrococcus, Brachybacterium, Microcella, Dietzia, and Rhodococcus (class Actinomycetia) and genera Paracoccus and Pseudomonas (class Proteobacteria). The culturable bacteria of the N2 sulfide ore deposit were represented by genera Bacillus, Oceanobacillus, Alicyclobacillus (class Bacilli) and genera Micrococcus and Agromyces (class Actinomycetia). The N2 deposit community contained the strain Nor9-1, which showed a high level of similarity with the Alicyclobacillus aeris ZJ-6 iron-/sulfur-oxidizing bacterium. The model systems showed a strong correlation (r² = 0.91-0.97) between the growth of the bacterial communities of the studied ores and changes in the concentrations of oxygen and carbon dioxide in the model atmosphere. Under the ecological optimum (specific growth rate of the culture constituting 0.519 d^-1) in 7 d, oxygen decreased to 0.34-1.48% and carbon dioxide increased to 7.44-14.88%. Under the ecological pessimum (restricted available organic carbon), given the predominant development of the chemolithotrophic group of bacteria (specific growth rate of 0.045 d^-1), changes in the respiratory gas concentrations constituted 0.9-2.7% of O₂ and 0.06-0.16% of CO₂. A relationship was established between the specific rate of O₂/CO₂ loss and specific growth rate of the bacterial communities. Thus, for the first time, indigenous cultivated aerobic bacteria of sulfide ores collected from the deposits of the Krasnoyarsk Territory were studied, and their effects on oxygen and carbon dioxide contents in the atmosphere of closed model systems were examined.