Seasonal variations in airborne bacterial community structures at a suburban site of central Japan over a 1-year time period using PCR-DGGE method

Airborne bacteria could affect human health and climate. In this study, the bacterial community structures were investigated by analyzing air samples collected from a suburban location in Toyama, central Japan. Sixty samples were collected almost weekly between March 2009 and February 2010. A cultivation-independent approach, PCR plus denaturing gradient gel electrophoresis (DGGE), was used to analyze changes in the structure of the airborne bacterial communities. The DGGE profiles showed significant differences between sampling days, reflecting quite different bacterial profiles. Sequencing of DGGE bands revealed that the bacterial community was dominated by gamma-Proteobacteria, Firmicutes, alpha-Proteobacteria, Bacteroidetes, and Actinobacteria. The most frequently observed genus was Pseudomonas, followed by Bacillus. The airborne bacterial assemblage in winter differed from that in the other seasons. The differences could be attributed a number of factors, such as temperature, relative humidity, wind direction, and snowfall. In spring, the largest number of bands was classified as plant chloroplasts, such as Japanese cedar (Cryptomeria japonica) and Pinus spp., which are the major pollen allergen sources in Japan. The airborne bacterial abundance estimated by real-time TaqMan PCR ranged from 1.1 x 10(3) to 1.3 x 10(5) cells m(-3).