1. Halophiles are salt-loving microorganisms that require salt for growth, whereas halotolerant microorganisms can grow in the presence of salt but do not require it. 2. Halophiles have developed several adaptive strategies to survive in high salt environments, including insulating their cells to prevent salt from entering, protecting against the toxic effects of sodium, and modifying their cellular metabolism to function optimally at high salt levels. 3. At the cellular level, halophiles maintain low intracellular sodium levels through mechanisms like active sodium extrusion pumps and plasma membranes that are less permeable to sodium than potassium. They also accumulate compatible solutes like glycerol that allow them to maintain a hydr

1. Presentation on
Halophiles : Adaptive Strategies
Name :- Ravi S. Hirani
Roll No. :- MIC18102
Mentor :- Mr. Yogesh Gopani

2. Basic Terminology
Halophiles VS Halotolerant
Salt lovers , Salt tolerators,
Req. salt for From other domain and
Growth minimum req.of salts

4. Habitat Of Salt lovers

5. Bacci Halli

6. Superpowers of Halophiles
• 1. Insulation :- Adaption which reduce outer environmental effect of
high salt concentration than interior, prevent entry of salts ( First line of
defence )
• 2. Protection :- Protects Inhibitory and toxic effect of Na+ ( Anything
More than Req. is Toxic )
• 3. Modification :- Show in cellular metabolism , show high level of
activity in high salinity.

7. Insulation
• High concentration of Na+ are generally as being toxic to most biological
systems, that’s why most bacteria , fungi and alga possess membrane with
a lower permeability to Na+ than K+.
• Also they shows active extrusion mechanisms to lower the intracellular Na+
content below the equilibrium value.
• Insulation of the cell from Na+ entry is clearly a feature of the osmotic
physiology of Halobacterium.
• Cell Na+ levels are lower than external Na+ levels by an order of K+
concentration are generally higher than external K+ concentration.

9. Protection
• All halotolerant and halophilic organisms show greater level of preventing
effect of NaCl by maintaining low plasma membrane Na+ permeability and
active Na+ extrusion.
• The intracellular Na+ levels of salt living organisms is generally high than
normal fresh water flora.
• Eg, Halotolerant Cynobacteria --- is 0.23 – 1.87 M NaCl
• Fresh water organisms --- is 0.05 M NaCl.

10. Compatible Solute Theory
• Microbes growing at high salt concentration facing combination of problem of
lower water potential and high intracellular Na+ content ( if insulation is
poor ).
• This theory suggested that water like hydroxyl groups of polyols (like
Glycerol,mannitol) can replace water molecules and thus maintain
hydrophobically enforced water structure within the cytoplasm under
conditions of lowered water potential.

11. • Recent research has shown that short term changes in intracellular Na+
levels may occur upon initial transfer of saline media.
• In the alga Dunaliella tertiolecta shown that intracellular Na+ increased by
approximately 0.13 M when cells were up shocked to a medium containing
additional NaCl 0.4 M.
• Rapid Na+ entry (2 Min) was followed by net Na+ extrusion from the cell,
and a new steady state level was achieved within 30 minutes.
• Similar transient increases in cell Na+ followed by net Na+ extrusion have
been reported for Dunallella parva and fresh water cyanobacteria
Synechococcus , although the time course for Na+ extrusion was extended
beyond 30 minutes.

12. Conclusion
• It is clear that need for protection against Na+ toxicity will be depends
upon the insulation against NaCl entry.
• 1) the maintenance of cytoplasmic water structure
• 2) protection against transient increase in intracellular salt levels.

13. Modification
• This category encompasses those features of cellular metabolism that have
been modified to function in an environment of elevated salt level, showing
no inhibition at high salt levels.
• The unique and specialized nature of Halobacterium and Halococcus , with
an absolute requirement for salt at more than 2 M , the adaptations have
been characterized to greatest extent in these microorganisms.
• They are unstable in solutions of low ionic strength ( less than 1-2 M ).

14. • This requirement for high levels of monovalent salts appears to be due
mainly to the acidic nature of the envelope proteins.
• The outer surface of each cell of halobacterium consist of a single
lipoprotein membrane with glycoprotein subunits on the outer surface and
the proteins within this envelope complex contain a substantial proportion
of aspartic acid and glutamic acid residues.
• The surface charge density is increased by acidic groups on the membrane
lipids.
• It would seem that these excess negative charges are shielded by the
presence of high concentration of cations, thus preventing mutual
repulsion, this is known as charge – shielding effect.

15. Responses of Halobacterium
• Three principal types of salt response for halobacterial enzymes
• 1) enzymes requiring more than 1 M salt , with maximum activity at 2-4
M,
• 2) enzymes with maximum activity at 0.5 – 1.5 M, inhibited by more
than 1.5 M NaCl
• 3) enzymes that are strongly inhibited by elevated NaCl concentration,
showing the highest activity in the absence of salt.

16. • The last categories includes the enzymes of fatty acid synthesis, because
synthesis of esterified fatty acids is minimal in cells of halobacterium. (
vestigial enzyme )
• Enzymes fall in type 1 associated with the cell membrane
• Type 2 fall in soluble cytoplasmic enzymes
• Both KCl and NaCl both give similar stimulation inhibition curves with type
1 and type 2, some exceptions are also there where KCl is less inhibitory
than NaCl.
• Type 1 & 2 is modified in the way they can active in elevated salt
concentration.

17. • Excess of acidic amino acid residues within the enzymes proteins, with
charge shielding at high salt concentration leading to long term stability.
• It is clear now that many of the modifications exhibited by halobacterium
and halococcus also lead to a requirement for high level of salt, both for
structural stability and for optimal physiological functioning.
• This types of modifications best explain halophilic rather than
halotolerant.