Q-176. Assessment of Metabolic Activity and Growth Capability of Bacteria in Air

E-K. Son, V. Krumins, G. Mainelis, D. E. Fennell;
Rutgers Univ., New Brunswick, NJ.

Little is known about the microbial ecology of air. Air is often considered a minor and transitory reservoir for microorganisms. While many microorganisms have been identified and enumerated in ambient air, there has been very little exploration of microbial activity and growth in natural bulk air. The objective of this study was to determine whether bacteria present in ambient air are active and growing. The activity of bacterial bioaerosols was tested in rotating reactors made from 0.32 m3 stainless-steel drums equipped with temperature, pressure and humidity sensors. Simple volatile organic compound (VOC) growth substrates (e.g., ethene and propene) were added to reactors containing natural bioaerosols or laboratory-generated bioaerosols of Pseudomonas fluorescens or Xanthobacter autotrophicus and also to reactors filled with sterile air or inactivated bioaerosols. Natural bioaerosols and those from VOC-enriched reactors were collected by liquid impingement and collection on a 0.2 μm membrane. Genomic DNA was obtained using the Ultraclean Soil DNA Kit (MoBio Laboratories, Inc.) modified by intensive cell lysis and freeze-thaw cycles. Bacterial growth and community changes were assessed using quantitative PCR (qPCR) and denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes. A qPCR standard of 102 to 109 gene copies was developed and qPCR successfully detected and quantified from 4x103 to 4x105 cells per liter of air. Reactors retained ethene with a half-life of 13.5 days, and inactivated P. fluorescens bioaerosol particles of size mode 0.5 to 0.7 µm with a half-life of 8.5 days. For X. autotrophicus this time frame encompassed 50 doubling times for growth on propene and 10 doubling times for growth on ethene based on literature reports, and thus, a length of time necessary to observe activity of these bacteria in the airborne state. We compared rates of loss of the VOCs in reactors with and without live natural or X. autotrophicus bioaerosols to assess biodegradation. We also compared the changes in concentration and community structure of bacteria in VOC-enriched natural air to those in un-enriched natural air.