Previously held under moratorium from 25 June 2018 until 24 February 2022Extremophiles 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.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