Sodium chloride affects microbial growth in different ways depending on the organism. Obligate halophiles require salt to survive and will lyse without it, while halotolerant organisms do not need salt but can tolerate some salinity. Halophiles are categorized based on their preferred salt concentrations: slight halophiles tolerate 1-6% salt, moderate 6-15%, and extreme 15-30%. Scientists control salt levels in culture media to selectively grow halophiles or inhibit non-halophilic microbes. Halophiles are found in briny and coastal environments and employ mechanisms like compatible solutes and potassium control to regulate osmotic pressure in high salinity conditions.

1. FACTORS AFFECTING MICROBIAL
GROWTH-
SALT CONCENTRATION
Ms Saajida Sultaaana Mahusook

2. • Sodium chloride (NaCl) is a nutrient that affects different
organisms in different ways.
• Obligate halophiles, are organisms which require salt to
survive and will lyse, or break open, if the salt level drops
to a low level.
• Halotolerant, organisms are those which don’t need salt
to survive but can tolerate moderately salty environments.
• Halophiles belong to a larger group called extremophiles
who thrive under extreme conditions.

4. • Slight halophiles thrive in environments that contain 1 - 6
% salt.
• Moderate halophiles prefer 6 - 15 % salt.
• Extreme halophiles enjoy the saltiest environments of all
at 15 - 30 % salt.
• Scientists use these categories to prepare culture medium
perfectly suited for the organisms they want to grow.
• Halotolerant organisms prefer salt-free environments but
can survive at slight or moderate salt levels.
• For non-halophiles, salt can be deadly. When scientists
want to inhibit the growth of non-halophiles in the
laboratory, they include salt in the culture medium to
prevent non-halophiles from growing. This is called a
selective medium.

5. Habitat:
Halophiles are present in brine ponds, salt mines, coastal
and deep-sea areas, and deserts. Halophiles are also
present in soy sauce, anchovies and sauerkraut.

6. Mechanisms for Saline Resistance
Compatible Solutes
• One mechanism halophiles use to survive in high concentrations of
salt is the synthesis of osmoprotectants, which are also known as
compatible solutes.
• Compatible solutes are small-molecular weight molecules present in
microorganisms namely trehalose, glycine betaine and α-glutamate,
while others are restricted to a few organisms.
• These work by balancing the internal osmotic pressure with the
external osmotic pressure, making the two solutions isotonic, or close
to it.
Potassium Control
• This mechanism is performed by pumping in large amounts of K+
ions into the cytoplasm.

7. Applications:
• Halophilic bacteria have been found to perform
fermentation, acetogenesis, sulfate reduction,
phototrophy, and methanogenesis.

8. • Reference:
https://sciencing.com/effects-salt-concentration-bacterial-
growth-5924409.html
https://microbewiki.kenyon.edu/index.php/Halophiles