Molecular analyses of airborne microbial community influenced by Asian dust events for the evaluation of their impacts on outdoor environments and public health

Abstract

대기질의 건강영향연구는 대부분 화학적 오염물질과 물리적 특성에 대한 것이었다. 하지만 최근 이러한 경향이 변화되고 있다. 대기 중 바이오에어로졸에 노출될 경우 감염성 질환, 급성독성, 알러지 및 암 발생과 연관성이 있다고 계속 보고되었다. 이에 따라 바이오에오로졸은 다른 유해대기오염물질과 마찬가지로 유해성 인자로서 인식되었으며, 대기 중 세균 및 곰팡이의 분포에 관한 연구가 이루어지고 있다. 특히, 황사와 같이 거대한 사막먼지가 대륙간 이동시에 미생물도 같이 이동될 수 있으며, 풍하지역 생태계 및 보건에 큰 영향을 미칠 가능성이 있다고 제기되어 왔다. 황사에 관한 연구는 황사입자의 이화학적 특성에 관한 연구가 대부분이었고, 황사시 대기 중 세균 및 곰팡이에 관한 연구는 일부였다. 하지만 이러한 연구는 배양법을 기본으로 하고 있어 배양되지 않는 다수의 세균 및 곰팡이에 대한 정보는 매우 제한적이었다. 본 연구에서는 황사가 대기 중 세균 및 곰팡이에 미치는 영향을 분석하고, 황사시 세균 및 곰팡이가 같이 이동하여 서울대기중 유입이 되는지를 파악하고자 하였다. 이를 위하여 미생물 배양과 함께 황사시와 비황사시 대기 중 총먼지 (TPS)를 DNA 추출하여 DGGE, 16S rDNA 및 ITS clone library를 수행하였다. 대기모니터링 자료 및 대기 미생물 밀도 자료를 같이 분석하였으며 DGGE 패턴과air mass trajectory와 같이 분석하였다. 또한 대기 중에 일반적으로 분포하지만 알러지성을 가진 8종의 곰팡이를 MSQPC법을 정량분석하였다. 그 결과, 황사시 대기 중 세균 및 곰팡이의 밀도는 입자상 물질과 비례하여 증가하고 비황사보다 통계적으로 유의하게 높은 것으로 나타났다. 특히 대기 입자상 물질과의 상관분석 결과, 비황사시와는 달리 황사시에만 대기 중 TSP 및 PM10과 세균 및 곰팡이 밀도와 높은 상관관계를 나타내었다. 16S rDNA및 ITS clone library 비교결과, 황사시에 세균 및 곰팡이 군집은 황사시와 비황사시 전혀 다른 구성을 하고 황사시 사막에서 유래된 종들이 검출되었다. 또한 황사 전후 DGGE band pattern이 급격하게 변화되어 황사시 급격하게 대기 중 세균군집이 전혀 다른 구성을 가지는 것으로 나타났다. MSQPCR 분석 결과 황사시 분석한 알러지성 곰팡이 밀도가 종에 따라5-13배 높은 것으로 나타났다. 이와 같은 결과는 황사가 대기 중 세균 및 곰팡이의 구성 및 밀도에 영향을 주는 것으로, 사막먼지와 더불어 세균 및 곰팡이가 이동하며 이로 인한 건강 및 생태계에 큰 영향을 미칠 가능성이 있음을 보여준다.

The air quality in perspectives of human health has predominantly been studied on chemical pollutants and physical states

however, this focus is changing. Many studies have reported that exposures to bioaerosols are associated with a wide range of health effects such as infectious diseases, acute toxic effects, allergies and cancer (Douwes et al., 2003

). Therefore, the bioaerosol became considered as health affecting factors such as hazardous air pollutants and many researchers studied the distribution of bacteria and fungi in atmospheric environment. The number of Asian dust (AD) events, huge transport of desert dusts, has been increasing rate in Seoul. Many studies on them pointed out that the dust-borne microorganisms may be transported to downwind area and have effect on their ecosystem and public health. Although most of studies on Asian dust events have been focused on the physiochemical characteristics of aerosol, several researches have been performed on the movement of bacteria and fungi in aerosol. However, these studies were based on culture-dependent method, which cannot give information on unculturable microbes. Moreover, bacterial and fungal taxonomic compositions have potentially important implications for human health since the health effects of bioaerosols is highly dependent on their species. The impacts of the Asian dust events on the atmospheric bacterial and fungal communities were assessed. Both of culture-dependent and -independent methods such as DGGE and 16S and ITS clone library were applied to measure the compositions and changes of communities. In addition, the correlation between bioaerosols and the parameters of air quality and meteorology were examined. Lastly, eight universal but allergenic fungi in the air were monitored by MSQPCR to understand their seasonal variations and associations with environmental parameters, and to evaluate their potential risks of human health. The bacterial concentration was significantly increased and the bacterial community structure was abruptly changed during AD events. During the days affected by AD, culturable bacterial population levels showed significant positive correlations with total suspended particulate (TSP) and PM10 (particulate matter with aerodynamic diameter < 10 µm), whereas no significant correlation was found during normal days. AD seemed to directly impact the airborne bacterial communities, as abrupt changes of denaturing gradient gel electrophoresis (DGGE)-band patterns and significant differences in the 16S rDNA clone library between normal days and AD were observed. The changes of DGGE patterns were in agreement with the shift of PM2.5 chemical composition, suggesting that the outdoor bacterial community was affected by the source and transport pathways of air masses. The airborne fungal concentrations during Asian dust event days (AD) was significantly higher than that of non-Asian dust (NAD) days according to a Mann-Whitney U test (P <0.005). Comparison of AD vs. NAD clones showed significant differences (P <0.05) using LIBSHUFF. In addition, the correlation of culturable fungal concentrations with PM10 concentrations was observed to be high for the AD while correlation coefficients of PM10 as well as other particulate parameters with airborne fungal concentrations were significantly negative for the NAD days during intensive monitoring periods (May to June, 2008). In addition, high proportions of uncultured soil fungus isolated from semi-arid regions were observed only in AD clone libraries. The level of E. nigrum and the total levels of the measured fungi as well as A. alternata measured by MSQPCR were significantly higher during the dust storm days It was found that Asian dust increased the airborne allergenic fungal levels up to 5-12 times depending on the species. These results revealed that Asian dust events have impacts on both of microbial concentrations and compositions, suggesting that this long range transport of desert dusts may significant effects on human health and ecology in downwind area. In addition, although the allergenic abundance by ITS clone library was high on NAD days, allergenic potentials by fungi in aerosols were considered to be higher during AD days because the concentrations of outdoor culturable fungi and allergenic fungi were higher.