Bacterial community composition in rainwater associated with synoptic weather in an area downwind of the Asian continent.

Bacteria are abundant in atmospheric waters and can be disseminated by precipitation to the surface of the Earth, potentially influencing ecosystems, public health and climate. However, data on bacterial communities in rainwater, especially on the association with weather, are very limited. In this study, rainwater was collected at the coastal city Kumamoto, southwestern Japan, in 2015. The bacterial communities in fourteen samples were identified using 16S rRNA sequencing and compared according to the rain types at the synoptic scale, i.e., cyclones, Meiyu and non-Meiyu stationary fronts, and typhoons. Diverse bacterial communities were present in all four types of rainwater and were dominated by the phyla Proteobacteria (37%), Bacteroidetes (16%), Cyanobacteria (14%), Actinobacteria (9%), Acidobacteria (8%) and Firmicutes (5%). Approximately half of the phyla (16 out of 33) were common among the rain types. The operational taxonomic units (OTUs) common among the four types of rainwater represented the majority (averagely 74%) of the sequences, indicating the predominance of common bacterial OTUs regardless of rain type. On the other hand, the synoptic weather systems and the origins of air masses associated with the rain likely resulted in distinct bacterial communities. High fractions of bacterial soil indicator taxa signified the large contribution of bacteria from soils. Genera containing ice nucleation-active bacteria were identified in all samples except one typhoon rain sample. Marine bacterial taxa, e.g., Pseudoalteromonas, Synechococcus and Marinobacter, were detected in several samples, indicating the dispersal of marine bacteria via clouds and rainwater. Fecal indicator bacteria were also detected in all samples. Thus, the bacteria in the four types of rainwater were characterized by largely overlapping communities with some differences in community composition, indicating that rain is an efficient pathway for the dissemination of bacterial communities in nature and links continental, marine and island ecosystems.

Applicability of LIVE/DEAD BacLight stain with glutaraldehyde fixation for the measurement of bacterial abundance and viability in rainwater.

Rainwater contains substantial bacteria and rain is an efficient pathway for the dissemination of bacteria from the atmosphere to land and water surfaces. However, quantitative information on rainwater bacteria is very limited due to the lack of a reliable method. In this study, the epifluorescence microscopy enumeration with the LIVE/DEAD BacLight Bacterial Viability Kit stain was verified to quantify the abundance of viable and non-viable bacterial cells in rainwater, with the 4',6-diamidino-2-phenylindole (DAPI) stain for the reference of total cell counts. Results showed that the total counts of bacterial cells by LIVE/DEAD BacLight staining were consistent with those by DAPI staining, and the average detection efficiency was (109±29)%. The ratio of cell count with glutaraldehyde fixation to that without fixation was (106±5)% on average. The bacterial concentration in negative control was usually an order of magnitude lower than that in rainwater samples. However, in case of small precipitation, the abundance in negative control could be more than that in rainwater samples. These results indicate that the enumeration with LIVE/DEAD BacLight bacterial viability assay coupled with glutaraldehyde fixation and careful negative control investigation is an approach applicable to the measurement of the concentration and viability of bacterial cells in rainwater.

Seasonal and diurnal variation of organic ultraviolet filters from personal care products used along the Japanese coast.

This study aimed to investigate the behavior of organic ultraviolet (UV) filters released by recreational activities along the Japanese coastline. Seasonal variations of organic UV filters in seawater were investigated at four different recreational beaches (Mogushi, Wakamiya, Tsurugahama, and Otachimisaki beaches) in both summer (July through August) and winter (December). Moreover, short time scale diurnal changes were monitored at Otachimisaki beach in summer. Of the four sunscreen agents tested in this study, two agents-2-ethylhexyl-4-methoxycinnamate (EHMC) and 2-ethylhexyl salicylate (EHS)-were detected in all samples, whereas octyl-dimethyl-p-aminobenzonic acid and 3-(4-methylbenzylidene)-camphor were lower than detection limits. In particular, EHMC, one of the most popular organic UV filters, was dominant. The highest concentration of EHMC was observed at 1,080 ng L(-1), a level that exceeds those of previous studies. Both EHMC and EHS concentrations showed significant (p < 0.05) seasonal variations with advancing summer suggesting direct input from recreational activities. The subsequent examination showed short time scale diurnal changes of organic UV filters on the beach. The results showed that diurnal changes in EHMC concentrations were correlated to the number of bathers. EHMC concentrations increased during the afternoon and decreased during the night, although complete attenuation during the night did not occur. EHMC persists along the coast due to low mobility and may persist the next day. This is the first study to show the natural attenuation behavior of organic UV filters along recreational beaches.