New specific indicators for qPCR monitoring of airborne microorganisms emitted by composting plants

Bioaerosols emitted from composting plants are an issue because of their potential harmful impact on public or workers’ health. There is a major lack of knowledge concerning the dispersal of airborne microorganisms emitted by composting plants and the consequent potential exposure of nearby residents. This inadequate knowledge is partly due to the fact that there is currently no method for specifically tracing these microorganisms in the air. The objective of this study was to validate the use of microbial groups as indicators of composting bioaerosols by comparing their concentration in air samples, whether impacted by composting activity or not. Three potential microbial indicators were chosen among the core species of composting bioaerosols. They belong to the genus Saccharopolyspora, to the Thermoactinomycetaceae and to the fungus Thermomyces. Quantitative PCR systems using TaqMan probes were designed to quantify each of the three phylotypes in air samples collected outdoors in natural environments and at composting plants. Compost-turning operations at industrial plants resulted in an increase in the concentration of the three phylotypes of at least 2 orders of magnitude when compared to the concentration measured in control samples collected upwind, and of at least 1 order of magnitude compared to the background concentration measured in natural environments unaffected by industrial activity. In conclusion, these three thermophilic phylotypes can be used as indicators of airborne microorganisms emitted by industrial composting plants. They may be particularly relevant in studying the dispersal of bioaerosols around composting plants and the exposure of nearby residents. This is the first time that indicators of compost bioaerosols have been validated by comparing their concentrations in impacted samples to their background levels in natural environments.

► Three novel microbial indicators of composting bioaerosols were identified.
► Specific qPCR systems were designed for each of them.
► Their background concentration in the air from natural environments was determined.
► An increase in concentrations during the turning of composting piles was demonstrated.
► These thermophilic microorganisms can be used to monitor composting bioaerosols.