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Environmental and genetic factors controlling biofilm growth and development in the domain Archaea Bethan Johnson (24292880) PUREID: 687245083 Archaea biofilm antibiotics heavy metals Archaeal species play key roles in environmental processes including the carbon cycle and broader biogeochemical processes. Environmental contamination by both heavy metals and antibiotics is a growing concern, as industrial activities release large quantities of both into ecosystems annually, harming biological systems and contributing to antibiotic resistance. This thesis investigates how environmental and genetic factors can affect biofilm formation within the archaeal domain, focusing on heavy metals and antibiotics in haloarchaeal species. Particular attention is given to the influence of copper and zinc, including their ability to drive evolution of elevated metal tolerance, and how this may co select for antibiotic resistance. Further chapters focus on genetic determinants of archaeal biofilm formation in Haloferax volcanii, focusing on both motility genes and putative heavy metal resistance genes. Within these studies, baseline values for Minimum Inhibitory Concentration (MIC), Minimum Biocidal Concentration (MBC), Minimum Biofilm Eradication Concentration (MBEC) and biofilm biomass (determined by crystal violet staining) were determined for H. volcanii. Directed evolution assays induced resistance to copper and zinc in H. volcanii, with numerous genes being identified such as rpl4, a ribosomal protein, and ctaA, a Heme A synthase protein being implicated in heavy metal resistance. When determining how motility may affect biofilm formation within the archaeal domain, transposon insertion mutants were identified that had motility defects. Differences in cell morphology were observed between mutants as well as increased MIC and MBC values compared to the H. volcanii control for the biocides copper sulphate and rifampicin, highlighting increased resistance to stressors. These results suggest that environmental stressors play a role in archaeal biofilm formation, with some biocides promoting biofilm formation at below MIC values. This study provides novel insights into archaeal biofilm formation by integrating culture-based assays with directed evolution, and genome sequencing to identify key environmental and factors influencing their formation.<br><br><i>Thesis is embargoed until 31 July 2028.</i> 2026-10-01T16:13:57Z Text Thesis 10.17034/32805701.v1 https://figshare.com/articles/thesis/Environmental_and_genetic_factors_controlling_biofilm_growth_and_development_in_the_domain_Archaea/32805701 All Rights Reserved Open Access after 2028-07-31