Diversity and dynamics in bacterial populations in marine bioaerosols

Airborne bacteria are omnipresent in the atmosphere, having a substantial impact on ecological patterns (distribution of organisms), medical concerns (spreading of pathogens) and climate functioning (condensation nuclei). Despite its unquestionable importance for ecosystem functioning, airborne bacteria, and particularly those in marine bioaerosols, are still clearly understudied. The absence of standardised methods further complicates proper comparison of the few studies on bioaerosols that exist to date. The current thesis aimed to gather basic knowledge about abundances and composition of bacterial communities in marine bioaerosols and how their spatial and seasonal dynamics may be affected by environmental factors. Furthermore, a complementing evaluation of quantification methods was performed to identify suitable procedures with the potential to be used in standardised investigations. All analyses were carried out using culture-independent methods (pyrosequencing, ARISA, q-PCR) in order to avoid any possible biases which would have been introduced by culture-dependent methods. The spatial aspect was studied in samples which were taken during a cruise with the research vessel Heincke from the North to Baltic Sea. A high-throughput sequencing approach revealed a highly diverse bacterial community in the samples with taxa that were typically associated with different areas of origin (plant, soil, marine, human). Wind direction and the sampling location were the most influential factors for the bacterial community composition. The current findings further support the existence of a bacterial core community in the atmosphere which may have a stronger influence on the bacterial community composition than the respective underlying ecosystem. A continuous yearlong sampling was carried out at the remote island of Helgoland to investigate the temporal aspects of marine bioaerosols. Changes in the bacterial community composition were displayed using the culture-independent fingerprint method ARISA and analysed in context of the environmental data. In addition to a seasonal effect which was probably caused by a species shift, the wind direction again had a clear effect on the airborne bacterial communities. Further speciesidentification is needed to elucidate which bacteria might have been responsible for the shift. Furthermore, there was a continuously high variability in bacterial community composition, regardless of the regarded timespan (intra-week = intramonth = intra-season = whole sampling period). This finding is a clear indication for an unstable airborne bacterial community at Helgoland. Associated with the yearlong sampling, two quantification methods were compared: a q-PCR and the direct counting of fluorescence particles using a FLAPS. The two quantification methods generated differential results. This was most likely caused by the FLAPS counting all biological particles (containing riboflavin and/or NAD(P)H), whereas the q-PCR specifically detected for bacteria. Thus, FLAPS does not seem to be well suited for outdoor investigations, underlining the urgent need for the standardisation of bioaerosol quantification. This important task needs to be addressed by future studies in order to facilitate comparable investigations, promoting our understanding of airborne bacteria in bioaerosols. All things considered, the current findings elucidated the highly diverse bacterial communities in marine bioaerosols which were subject to strong temporal and spatial fluctuations. The evaluation of modern methodologies to assess this diversity clearly underlined the urgent need for further investigations. Therefore, the current thesis represents an important step towards a better understanding of patterns and processes within airborne bacterial communities, thereby advancing our knowledge on bioaerosols and their driving factors.