Investigation into the Physiology and Ecology of Antarctic Nanohaloarchaeota

• Main Author: Hamm, Joshua
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UNSW, Sydney 2020
• Subjects: Antarctica; Nanohaloarchaeota; Archaea; Antarctic; Antarc*; antarcticus
• Online Access: http://hdl.handle.net/1959.4/70434; https://unsworks.unsw.edu.au/bitstreams/aca4fc8b-445c-49fc-be18-d9ba63463eb3/download; https://doi.org/10.26190/unsworks/22190

The Nanohaloarchaeota are a diverse archaeal lineage that are ubiquitous amongst hypersaline microbial communities. During my Honours thesis, enrichment cultures were produced that supported proliferation of an Antarctic Nanohaloarchaeota (Candidatus Nanohaloarchaeum antarcticus) from Rauer 1 Lake, Antarctica, providing the opportunity to expand understanding of nanohaloarchaeal ecophysiology. Cultivation experiments and genomic analyses concluded that Ca. Nha. antarcticus is incapable of independent growth and requires direct cell-cell contact with another organism. In this thesis, the physiology and ecology of Ca. Nha. antarcticus was investigated through an array of techniques including fluorescence microscopy, electron microscopy, metagenomics, metaproteomics, and phylogenetics. Cultivation and fluorescence microscopy experiments revealed the host of Ca. Nha. antarcticus to be Hrr. lacusprofundi. Genomics and proteomics analyses of Ca. Nha. antarcticus concluded that the nanohaloarchaeon is reliant on Hrr. lacusprofundi for essential compounds including nucleotides, amino acids, lipids, and vitamins. Fluorescence activated cell sorting enabled purification of pure Ca. Nha. antarcticus cells which were used to produce pure co-cultures with Hrr. lacusprofundi. Cultivation experiments indicated that 10 out of 16 tested Hrr. Lacusprofundi strains were capable of supporting proliferation of Ca. Nha. antarcticus during initial growth of pure co-cultures Interactions between Ca. Nha. antarcticus were shown to involve uptake of 16S rRNA from Hrr. lacusprofundi and the formation of long cytoplasmic bridges extending outwards from nanohaloarchaeal cells. An unusually large (5998 amino acids) open reading frame was identified in the Ca. Nha. antarcticus R1 metagenome assembled genome with functional domains indicating a possible role in mediating interactions with Hrr. lacusprofundi. The nanohaloarchaeal community in Antarctic hypersaline systems had a low level of variation with the exception of genomic islands ...