The atmospheric dispersion of bacteria over long distances is an important facet of microbial ecology. Certain groups of dispersed bacteria can adapt to their new location and affect established ecosystems. Aeolian dust particles are known to be carriers of microbes but further research is needed to expand our understanding of this field of microbiology. Here we showed the potential of aeolian dust to global migration of bacterial cells. We demonstrated the presence of microbial cells on dust particles directly by bio-imaging. Bacterial abundance on dust particles declined from 10 5 to less than 10 3 cells/m 3 as the dust event subsided. Taxonomically diverse bacteria were identified by 16S rRNA gene sequencing and some of these bacteria retained growth potential. Our results confirm that bacteria can attach to aeolian dust particles and they have the potential to migrate globally during dust events and thus can contribute to the diversity of downwind ecosystems.

Recent whole-genome analysis suggests that lateral gene transfer by bacteriophages has contributed significantly to the genetic diversity of bacteria. To accurately determine the frequency of phage-mediated gene transfer, we employed cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) and investigated the movement of the ampicillin resistance gene among Escherichia coli cells mediated by phage at the single-cell level. Phages P1 and T4 and the newly isolated E. coli phage EC10 were used as vectors. The transduction frequencies determined by conventional plating were 3 ؋ 10 ؊8 to 2 ؋ 10 ؊6 , 1 ؋ 10 ؊8 to 4 ؋ 10 ؊8 , and <4 ؋ 10 ؊9 to 4 ؋ 10 ؊8 per PFU for phages P1, T4, and EC10, respectively. The frequencies of DNA transfer determined by CPRINS-FISH were 7 ؋ 10 ؊4 to 1 ؋ 10 ؊3 , 9 ؋ 10 ؊4 to 3 ؋ 10 ؊3 , and 5 ؋ 10 ؊4 to 4 ؋ 10 ؊3 for phages P1, T4, and EC10, respectively. Direct viable counting combined with CPRINS-FISH revealed that more than 20% of the cells carrying the transferred gene retained their viabilities. These results revealed that the difference in the number of viable cells carrying the transferred gene and the number of cells capable of growth on the selective medium was 3 to 4 orders of magnitude, indicating that phage-mediated exchange of DNA sequences among bacteria occurs with unexpectedly high frequency.Recent nucleotide and whole-genome analyses have revealed that most bacterial genomes contain large amounts of bacteriophage DNA (18). This finding suggests that lateral gene transfer by bacteriophages has contributed significantly to the acquisition of new genetic traits, the ability of bacteria to exploit new environments, and the genetic diversity of bacteria (27). Since bacteriophage-mediated gene transfer was first recognized (32), transduction has been found to occur in many phage-host systems, and various aspects of transduction, including molecular mechanisms, physiologic and genetic characterization of transductants, and ideal environments for transduction, have been investigated (29).For nearly a half-century, culture methods using selective agar media have played a leading role in the study of gene transfer (5). Genetic characteristics such as amino acid deficiency repair and antibiotic resistance have been used for selection of transductants (9). Transduction frequencies were shown to differ over orders of magnitude from 10 Ϫ11 to 10 Ϫ5 per bacteriophage, which are lower than those for conjugation and transformation (14, 27). However, current knowledge of horizontal gene transfer via bacteriophages in the environment is rather limited because of methodological constraints. Conventional methods for the detection of gene transfer depend on high levels of gene expression and culturability on selective media. Although these methods have led to an understanding of the genetic and physiologic characteristics of transductants and the molecular mechanism of transduction, they have limited abilities to quantify the genetic material introduced into individua...

Asian dust (called 'Kosa' in Japan) is comprised of a large number of soil particles originating from the arid regions and deserts of China and Mongolia and dispersed long-range to Japan. A major public concern about Asian dust is its impact on human health. We collected Asian dust particles over the Japan Sea at an altitude of 900 m to directly estimate their effects on health. We examined the properties of the collected particles on wet surfaces. Through size distribution measurements and scanning electron microscopy with energy dispersive X-ray (SEM-EDX) analysis, we demonstrated that small dust particles (less than 1 µm) form aggregations with water-soluble salts such as calcium and sodium and they are transported to Japan as aggregates. These aggregates probably break down into small particles on nasal mucous membranes and may cause adverse respiratory health effects.Key words Asian dust; health effect; particle size; scanning electron microscopy with energy dispersive Xray Aeolian dust is comprised of large numbers of soil particles originating from arid regions and deserts, and transported long distances through the air. Major aeolian dust events are "African dust" from the Sahara and Sahel deserts, "Australian dust" from the Australian desert, and "Asian dust (called Kosa in Japan)" from the Taklamakan desert, Gobi desert, and the Loess plateau. Over one million tons of Asian dust particles are estimated to fall to the ground in Japan each year; 1) 3000-5000 km away from their sources. A major public concern about Asian dust is its potential risk to human health.It has been reported that aeolian dust particles such as Asian dust particles may induce inflammatory diseases such as allergies, and aggravate symptoms of pollen allergies.2) It is well known that Asian dust particles transported to Japan adsorb various chemical species such as sulfates, nitrates, and polycyclic aromatic hydrocarbons derived from air pollutants.3-5) Chemical compounds on Asian dust particles are likely to have harmful health effects. Examining the effects of these particles on health is also important because small particles usually have adverse health effects including respiratory inflammation.6,7) Such investigations are lacking because of the difficulty of collecting Asian dust particles without contamination from ground soil particles in the destination countries. We collected Asian dust particles over the Japan Sea at an altitude of 900 m, to estimate directly their impact on health; we considered their properties on wet surfaces such as mucous membranes. Our research is the first step towards understanding the health effects of Asian dust "particles." MATERIALS AND METHODS Collection of Asian Dust ParticlesThe occurrence of an Asian dust event and its drift were confirmed by LIDAR (Light Detection and Ranging) data from the Ministry of the Environment, Japan (http://www-gis5.nies.go.jp/eastasia/ DustLider.php), and Asian dust information from Japan Meteorological Agency (http://www.jma.go.jp/jp/kosa/index.html), as well as...