Molecular microbial ecology of Polar aerial environments

Cuthbertson, Lewis Paul (2019) Molecular microbial ecology of Polar aerial environments. Doctoral thesis, Northumbria University.

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Abstract

The biodiversity of bacterial communities in the Polar atmosphere is understudied, and as a result, the degree to which these communities influence macroecological patterns of biodiversity is poorly understood. This study aimed to investigate the bacterial biodiversity of the atmosphere by testing the hypothesis that bacteria are ubiquitous and present in polar air as heterogeneous communities. The study found bacterial DNA in all samples collected from both Poles, and whilst a degree of heterogeneity was observed in Arctic bacterial communities, there was an unexpectedly high level of sequence in the Antarctic.

Currently, there is no consensus as to the most appropriate bioaerosol sampling method, and the degree to which sampling methodology impacts the results of bioaerosol studies is still unknown. This variability was assessed by testing the hypothesis that bacterial community profiles in Polar air samples are not influenced by sampling methodology. However, the findings suggest that choice of bioaerosol sampling methodology can have a strong impact on the biodiversity observed.

The high level of sequence diversity in Antarctic air samples led to an investigation of technical variation as a result of their low biomass; and from this, it was found that the lower limit of biomass for a successful community description using an Illumina MiSeq approach was 1x106 CFU per mL-1, and that the lower limit at which this concentration of bacteria could be extracted using the most commonly used commercial DNA extraction kit was 1x107 CFU per mL-1.

Antarctic bioaerosol samples were found to have considerably lower biomass than these limits, suggesting that the results obtained were, in part due to technical variation as a result of their low biomass. The choice of bioinformatics pipeline was also investigated for low biomass samples, and found to have no effect on the final outcome. Overall, the study showed that the Polar atmosphere contains very low biomass and that the pattern of biodiversity in this low biomass environment was both variable and not linked to physical or chemical environmental parameters. Hence, the atmosphere may act as a barrier to dispersal both into and out of the Polar regions.

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