Airborne microorganisms in gypsum maze caves of the western Ukraine: biodiversity and geoecological control

Abstract

Microbiological and microclimatic studies of two giant gypsum caves in Bukovina (Prypruttia) and Podillya, Ukraine, have characterized the microbial air quality and the microclimate within them, via stationary air sampling using the volumetric (impact) method. Dominant species of bacteria and fungi were identified by MALDI-TOF mass spectrometry by comparing the mass spectra of ribosomal proteins (molecular fingerprints) with the spectra in a database. Basic meteorological elements such as air temperature, air humidity, and airflow velocity were measured. Bacterial aerosol concentrations ranged from 37 to 232 CFU × m–3 in the indoor air of the caves, and for fungi from 10 to 365 CFU × m–3. The range of bacterial aerosol concentrations in the outdoor environment ranged from 140 to 535 CFU × m–3, being significantly higher than inside the caves. The most common microorganisms in the cave air were mesophilic Gram-positive cocci (Staphylococcus), non-spore-forming Gram-positive rods (Arthrobacter and Rhodococcus) as well as Bacillus and Lactobacillus, mesophilic actinobacteria (Streptomyces) and filamentous fungi (Alternaria, Penicillium). The microclimatic measurements carried out in both caves testify to the high stability of temperature and humidity. Measurements made using the katathermometric method showed that the speed of air movement in the static part of both caves ranges between 0.01 and 0.03 m × s–1. The stability of the microclimatic conditions of the cave interior suggests that most microorganisms come from outside and enter the caves during an exchange of air with the external environment. In general, the concentration of microorganisms in the air of these caves is characterized by significant spatial variation within the cave fields but clearly tends to decrease as one moves away from the cave entrance. Our study shows that the content of airborne microorganisms and their spatial distribution in caves are determined by both external factors and the environment of the caves’ interior, especially microclimatic, morphometric and morphological factors such as the cave volume, size of the chambers and corridors and maze structure.