An Investigation into the Motility of Environmental Haloarchaeal Species

This work uses holographic microscopy (and other optical microscopy techniques) to explore the swimming behaviours of three environmental strains of haloarchaea. Archaea extracted from two highly saline environments; The Great Salt Lake, Utah and Boulby Potash Mine, UK were sequenced to discover species identity and motility appendage structure. Optimal growth conditions were established, through the use of spectrophotometry and dark field spectroscopy. Thousands of cells were then simultaneously tracked in three-dimensions, using digital holographic microscopy (DIHM). The tracks were computationally analysed and motility features extracted. This thesis represents the first example of exploration into the three-dimensional swimming behaviours of any haloarchaeal species. Genetic sequencing revealed samples of Haloarcula hispanica and Haloferax volcanii extracted from the Great Salt Lake and Boulby Mine respectively. Flagella genes from the samples highlighted variations in the composition of the archaellum structure of two samples of H. hispanica and a further variant in Hx. volcanii. DIHM experiments resulted in similar swimming behaviours across the three samples tested. The haloarchaeal cells swam very slowly, with average speeds of ≈ 2μm/s. Cells typically reorientated much less frequently than bacterial counterparts (≈ every 10-15 seconds on average). Furthermore, individuals displayed the previously characterised ‘run-reverse’ reorientation type, without the ‘flick’ associated with having a flagella hook. All samples were affected by high levels of Brownian rotation and an interesting, ‘wobble’ movement. Overall this project aims to fully evaluate the motile behaviours of archaeal samples extracted directly from their natural habitats, in an attempt to gain further insight into microorganisms living in extreme hypersaline environments.