Bacterial Aerosol Diversity in Snow and Outdoor Air Samples Collected in Bejing During Jan-March, 2010

Fangxia Shen and MAOSHENG YAO

State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering Peking University, Beijing 100871, China

     Abstract Number: 373
     Last modified: May 11, 2010

Abstract
The possible roles of bioaerosols as a cloud condensation nuclei in climate change are getting increased attention. In this study, snow samples were collected at different locations within 4th ring of Beijing in five consecutive snow events during the period of Jan-March, 2010. Outdoor air samples were also collected using mixed cellulose ester (MCE) filter. The conductances of the snow samples, distilled water and tap water were measured using a lock-in-amplifier with an amplitude of 50 mV at different frequencies (10-100 kHz). The total bacteria in snow samples were amplified using quantitative polymerase chain reaction (qPCR) in three separate manners: direct amplification, after agar plate culturing and after liquid culturing. The outdoor air samples were amplified after direct culturing of filter samples on agar plate. The PCR products were further analyzed using denaturing gradient gel electrophoresis (DGGE). In addition, both snow samples after melting and air samples were incubated at three different temperatures: 4 oC, 26 oC, and 37 oC, and the colony forming units (CFU) were manually counted.

The conductance levels of snow samples were found similar at tested frequencies, substantially lower than that of tap water and higher than that of distilled water. For all snow samples, the conductance was found to have a sharp increase at 10 kHz. PCR-DGGE results indicated that different snow samples had the same bacterial aerosol diversity as that of outdoor air samples. In most cases, PCR-DGGE after sample culturing resulted in higher intensity bands than the direct PCR-DGGE. Preliminary data indicated that the culturing of both snow and outdoor air samples at 26 oC resulted in higher CFU counts than other two temperatures tested. Snow samples were observed to have CFU counts of 100 to 10000 per ml in this study. These data suggest that there exist an abundance of bacterial species in the snow samples, similar to those found in outdoor air at the ground. The atmospheric mixing might have played a role in this regard.