**8. Microbial diversity study in the atmosphere of the Iberian Peninsula after a Saharan dust intrusion**

Four aerobiology sampling flights took place during February and March 2017 using the CASA C-212-200 aircraft from INTA. The study focused on microbial diversity in the atmosphere of the Iberian Peninsula during and after a Saharan dust intrusion. Flights took place under four different conditions: (1) during a strong Sahara dust storm that reached the north of the Iberian Peninsula, from February 22 to 24, 2017 (February 23, 2017) (**Figure 7**); (2) following precipitation (February 28, 2017); (3) following a dry period (March 8, 2017); and (4) along the northern coast of Spain (March 9, 2017). In each flight, samples were collected at different altitudes, and air samples were obtained simultaneously at ground level. A total of 20 samples were collected and are being analyzed. Cell presence was observed by scanning electron microscopy (SEM), and bacterial diversity is being studied by DNA extraction, 16S rRNA gene amplification, and Illumina MiSeq sequencing. Results are being analyzed via bioinformatics and biostatistical software (MOTHUR, SPSS, STAMP, CANOCO, and PAST) which will allow us to compare the results between the different flows and scenarios.

Although this study is not yet finished, some data can be advanced in this chapter. **Figure 6** shows SEM microphotographs obtained from samples in different scenarios. In general, the samples obtained during the days of dust intrusion (flight

**Figure 7.**

*Saharan dust intrusion. Dust pours off the northweat Afrincan coast and blankets the Iberian Peninsula, 23 February, 2016. NASA satelital imagen via MODIS.*

of February 23) appear completely covered with mineral particles. In these cases, more biological cells were detected than in the rest of the days. In the particular case of samples from the marine coast flight, more diatoms were observed (**Figure 6E**).

The analysis of diversity using the Shannon index showed that, in all cases, diversity was greater on days of Saharan dust intrusion, both in the samples taken from the ground and those taken at higher altitudes with the aircraft. This indicates that Saharan dust contributes microorganisms that are not present in the atmosphere on a daily basis. Diversity analysis showed phylum characteristics of soils, being *Alpha*- and *Betaproteobacteria* the most abundant classes. All of the analyses performed showed that bacterial diversity detected at ground level and in-flight samples during the dust intrusion event were similar among one another. The genus taxonomic levels of *Sphingomonas*, *Geodermatophilus*, *Methylobacter*, *Rhizobiales*, *Bacillus*, or *Clostridium* were present in every sample, but their sequences were more abundant in the case of ground samples and dust intrusion samples collected during the day flight. However, sequences of the genus *Flavobacterium*, *Streptococcus*, or *Cupriavidus* were most abundant in the case of samples collected during flight.

Preliminary conclusions show that bacterial diversity of airborne bacteria during days of dust intrusion is higher and similar to bacterial diversity commonly detected in soil samples. Further analyses are being conducted with these samples to obtain a complete description of the evolution of bacterial diversity during those days.
