Bacterial ion effects and their relation to salt tolerance

  • Rosemary Orr

Student thesis: Doctoral Thesis

Abstract

Extremophiles are organisms that are able to tolerate conditions that would otherwise inhibit or even kill non-extremophilic organisms - such extremes include acidity, high salt concentrations, high temperatures and high pressure. Specifically, halophiles are organisms that have a requirement for high concentrations of salt for growth. These organisms have been found to use either of two adaptation strategies, known as 'salt-in' (accumulation of inorganic ions) and 'salt-out' (removal of inorganic ions and accumulation of neutral molecules). In the current study, the relationship between the level of salt tolerance of an organism and its ion metabolism was investigated in order to gain insight into halo-adaptation and mechanisms of bacterial salt tolerance. This was accomplished by analysing the effects of a variety of salts (21 different combinations) on a halophile (Salinibacter ruber), non-halophile (Escherchia coli) and halotolerant (Echinicola vietnamensis) organism, which was achieved via an analysis of the effects of salts on bacterial growth, intracellular cation accumulation, enzymatic activity and and bioinformatics analysis. It was found that cation preferences were directly related to the level of salt tolerance of the organism, which is hypothesised to be a product of proteome acidity as well as the presence of specific membrane cation transporters. Specifically, the preference of S. ruber for the higher charge density Na+ over K+ may be rationalised based on the Hofmeister effect -i.e. this cation may provide better stabilisation of intracellular enzymes at the optimal salt concentrations for growth of S. ruber, but may be destabilising if accumulated at higher concentrations, and for non-salt adapted organisms. The ability of E. vietnamensis to tolerate and utilise many non-physiological ions supports this theory. Additionally, E. vietnamensis was postulated to use a 'hybrid' osmotic adaptation strategy - this organism may have industrial applications due to its large salt concentration tolerance range and high tolerance for non-physiological cations. Crucially, it was also found that E. vietnamensis and S. ruber contained membrane cation transporters that may be essential for their salt tolerance, giving insight into the essential nature of these proteins for the possession of salt resistance, which may have potential to be utilised for the transfer of salt- tolerance to commercially important organisms. Finally, one specific salt combination tested, equimolar LiCl + KBr proved to totally inhibit bacterial growth and may show promise as an antimicrobial agent, for which a patent application has been initiated. The results of the current study can have various applications, including those within industry, medicine and astrobiology.
Date of Award16 Mar 2018
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorMaxim Fedorov (Supervisor) & Neil Hunt (Supervisor)

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