Halophiles are microorganisms that require high salt concentrations to survive and grow. They are found in hypersaline environments around the world. There are three main types of halophiles based on their salt requirements: slightly halophilic microbes grow best at 2-5% salt, moderate halophiles at 5-20% salt, and extreme halophiles, like Halobacterium salinarum, require at least 9% salt with optimal growth at 12-23% salt. Halophiles have adapted mechanisms like accumulating compatible solutes to balance osmotic pressure and transporting sodium ions to maintain cellular integrity in hypersaline conditions. Some halophiles have industrial applications involving carotenoid pigments, fermentation

1. PRESENTED BY :- SADAAT ALTAF
MSC.MICROBIOLOGY
2ND SEMESTER
UNIVERSITY OF KASHMIR

2. CONTENTS
 Introduction
 Taxonomy & Classification
 Distribution
 Types
 Characteristics
 Adaptation mechanism
 Applications

3. INTRODUCTION TO HALOPHILES
 Halophiles (Greek word for salt loving) are microorganisms that
require certain concentration of salt to survive and grow.
 Halophiles are represented by certain species of archeae, bacteria and
eukaryotes for which the main characteristic is their salt requirement.
 One definition of halophiles is that of Oren, who defines them as
“microorganisms with optimal growth at salt concentration of over
0.2M”.
 In Eubacteria, halophiles are a very heterogenous group,having
members in at least eight different phyla.
 In Archeae, halophilism is strictly limited to members of Haloarchaea
class and Nanohaloarchaea subphylum.
 Some eukaryotic halophiles are, alga Dunaliella salina and fungus
Wallemia ichthyophaga.

4. TAXONOMY
 Methods of chemotaxonomy,multilocus sequence analysis, numerical
taxonomy, comparative genomics and proteomics have allowed
taxonomists to classify halophiles.
 These versatile microorganisms occupy all three major domains of life,
the Archeae (21.1%) , Bacteria (50.1%) and Eukarya ( 27.9%).
 The halophilic archeae come under the group, Euryarchaeota, which
comprise a physiologically diverse group of Archaea.
 This euryarchaeal group currently has 50 genera and 213 species in one
of family Halobacteriaceae (2016) , which are extremely halophilic,
aerobic members of Archaea.
DOMAIN – Archaea
PHYLUM – Euryarcheota
ORDER- Halobacteriales
FAMILY- Halobacteriaceae

6. IMPORTANT GENERA
 The haloarchaea are a distinct evolutionary branch of Archaea
distinguished by possession of ether linked lipids and absence of
murein in their cell walls.
 In the order Halobacteriales there are 6 important families
1. Halobacteriaceae ( Type genera- Halobacterium)
2. Haloarculaceae ( Type genera- Haloarcula)
3. Halococcaceae ( Type genera-Halocoocus)
4. Haloferacaceae ( Type genera- Haloferax)
5. Halorubraceae ( Type genera- Halorubrum)
6. Nitrialbales (Type genera – Natrialba)

7. DISTRIBUTION/ OCCURENCE
 Halophiles are found distributed all over the world in hypersaline
environments. Hypersaline environments are generally defined as those
containing salt concentrations in excess (3.5 % total dissolved salts).
 Many hypersaline bodies are formed by evaporation of sea water and are
called thalassic with salinity upto 3-3.5 mol/L, a point at which extreme
halophiles can grow eg Halobacterium.
 Waters in which salts are of nonmarine proportion, due to precipitation of
NaCl , leaving high concentration of potassium and magnesium salts are
called Athalassic which mark the upper limit of resistance of all
biological forms.
 They are found in natural hypersaline brines in arid, coastal and even
deep sea locations as well as in artificial salterns used to mine salts from
the sea.
 They inhabit natural environments high in salt such as solar evaporation
ponds and salt lakes or artificial saline habitats such as surfaces of heavily
salted foods, like certain fish and meats.

8.  They are found in marine salterns, salt marshes, subterranean salt
deposits, carbonate springs, alkaline soils and soda lakes.
 The two largest and best studied hypersaline lakes are
1. Great salt lake in Utah ,USA in which ratio of ions is similar to that in
seawater but absolute concentration of ions are about 10 times more than
sea water. It is slightly alkaline in pH
2. Dead Sea in the middle east between Jordan an Israel which contains
very high concentration of magnesium salts and relatively lower
concentration of sodium ions. It is slightly acidic in pH
 Many small evaporation ponds or sabkhas are found near coastal areas.
Notable among these are Solar lake,Gavish Sabkha and Ras Muhammad
Pool near Red Sea coast.
 Hypersaline evaporation ponds have also been found in Antarctica (Deep
Lake , Organic Lake ) several of which are stratified with respect to salinity.
 A number of alkaline hypersaline soda brines also exist including the Wadi
Natrun lakes of Egypt, Lake Magadi in Kenya and Great Basin lakes of
Western United States, several of which are intermittently dry. Soda brines
are lacking in magnesium and calcium divalent cations because of their low
solubility at alkaline ph

9.  Soda lakes are highly alkaline hypersaline environments and their
water chemistry resembles that of hypersaline lakes such as Great salt
lake but because high levels of carbonate minerals are also present in
the surrounding strata ph of soda lakes is quite high
 Marine salterns are also habitats for extreme halophiles . These are
small, enclosed basins filled with seawater that are left to evaporate,
yeilding solar sea salt. As salterns approach minimum salinity limits for
extreme halophiles, the water turns reddish purple in color due to
massive growth called bloom of Halophilic Archaea (due to presence of
carotenoids and other pigments).
 Extreme halophiles are also present in highly salted foods such as
certain types of sausages, marine fish and salted pork.
 Artificial salterns that have been constructed for production of sea salts
can also harbour halophiles.
 Hypersaline can also occur in deep sea basins created by evaporation
and flooding of ancient seas.

11. TYPES OF HALOPHILES
 Halophiles generally require about atleast 1.5 M NaCl (8%) , 3-4 M
NaCl (17-23%) for optimal growth but still some survive at salt
concentration of about 36%.
 Halophiles are categorized into 3 types on basis of their requirement of
NaCl or by the extent of their halotolerance
1. Slightly Halophilic - they grow best in concentrations of salt
around 2-5% eg Erythrobacter flavus, Staphylococcus aureus
2. Moderate Halophiles - they grow best in concentrations of salt
around 5-20% eg Desulfohalobium
3. Extreme Halophiles –they grow best at very high salt
concentrations around 20-30% with aleast 9% requirement for salt
and optimum 12-23% eg Salinibacter ruber, Halobacterium
salinarium
Halotolerant organisms are those which can withstand or toleate
some reduction in water activity of their environment but grow best in
absence of added solute.

13. CHARACTERISTICS OF HALOPHILES
 Most of the halophiles are aerobic chemoorganotrophs with respiratory
metabolism.
 Aerobic halophiles include Halomonas halmophila and anaerobic
halophiles include Halobacteriods halobius.
 On defined media, they use carbohydrates or simple compouns like
glycerol and organic or amino acids as their carbon source.
 They are found in variety of shapes including cubes, pyramids in
addition to rods and cocci.
 They are usually non motile but few strains are motile by archealla.
 They reproduce by binary fission and do not form spores
 Halobacterium was first to be described in this group.
 Natronobacterium, Nitronomonas differ from other extreme
halophiles in being extremely alkaliphilic as well as halophilic.
 Extremely halophilic archaea stain gram negative

14.  Genomes of Halobacterium and Halococcus are unusual in that large
plasmid containing upto 25-30% of total cellular DNA are often
present. Plasmids from extreme halophiles are among largesr naturally
occuring plasmids known and might actually be small chromosomes.
BACTERIORHODOPSINS
 Species of Halobacterium carry out light driven synthesis of ATP which
occurs without chlorophyll pigments .
 They have Light sensitive pigments with red and orange carotenoids
called bacteriorubrins
 under low aeration they synthesize and insert protein
bacteriorhodopsin into cell membrane that mediates ATP production
and supports slow growth of the organism under anoxic conditions.
 Halorhodopsins are also present which pump chlorine ions into the
cell.
 Sensory rhodopsins control photaxis that is the flagellar rotation,
moving towards light.

16. ADAPTATION MECHANISM
 Microbial cells must withstand osmotic forces that withstand life. Halophiles
use two strategies to cope with osmotic stress
1. Compatible solutes :- They increase cytoplasmic osmolarity by
accumulating small organic molecules called compatible solutes which
include glycine, betaine, polyols, ectione and amino acids. These counteract
the tendency of cells to become dehydrated under conditions of high
osmotic strength by placing cells in positive water balance.
2. Salt In Approach :- some halophiles use Na/K antiporters and K
symporters to concentrate KCl and NaCl to levels equivalent to external
environment. The protiens of these microbes have hydrophobic amino acid
residues which tend to be loacted on surface of folded protein, where they
attract cations, which form a hydrated shell around the protein thereby
maintaining its solubility.
 Cell wall of Halobacterium is composed of glycoproteins and stabilized
by Na. Sodium ions bind to outer surface of cell wall and are essential for
maintaining cellular integrity. When insufficient Na is present , cell wall
breaks apart and cell lyses.
 Ribosomes also require high K levels for stability. Cellular components
exposed to external environment require high Na whereas internal
components require high K.

17. APPLICATIONS
Industrial application
 Carotene from carotene rich halobacteria and halophilic algae can be used
as food additive or as food coloring agent. it may also improve dough
quality for baking bread.
 Halophilic organisms can be used in fermentation of soy sauce and Thai
fish sauce eg Halobacterium salinarium
 Ectione is commercially produced by extracting the compound from
halophilic bacteria Halomonas elongata by bacterial milking process. It
can protect unstable enzymes, nucleic acid against high salinity, thermal
denaturation and desiccation and freezing therefore it can be used to
increase shelf life of enzymes.
 It stabilizes activity of trypsin and chymotrypsin
 Rhodopsins can reduce sunburn when exposed to UV light
 It also inhibits aggregation and neurotoxicity of Alzheimer’s beta amyloid.
 They store Poly beta hydroxyalkanoate (PHA) which is used for production
of biodegradable plastics.
 Thus they play a significant role in industry with large number of
applications with fermented food products, cosmetics, preservatives,
manufacturing of bioplastics, photoelectric devices, artificial retinas,
holograms, biosensors etc.

18. Medical application
 the great metabolic diversity and the characteristics of halophilic
microorganisms makes them promising candidate and hope for drug
discovery.
 Haloarchae were first members of archaea found to produce bacteriocins
named halocins. They are peptide or protien antibiotics secreted into the
environment to kill or inhibit the sensitive haloarchael strains that occupy
the same niche.
Environmental applications
 Processes of biological wastewater treatment to remove organic carbon and
toxic compounds is facilitated by several halophiles eg the Dunaliella
growth facilitates wastewater treatment in oxidation ponds.
 Studies have proved that through addition of Halobacterium salinarium
degradation of wastes is improved.
 They can be used to remove toxic materials such as lead, phosphorus and
cadmium from contaminated materials.
 Biofuel production the halophilic alga Dunaliella salina is commericial
source of beta carotene and as potential source of glycerol production
which may also be considered as a raw material for biofuel production.
 Genetically engineered halophilic enzymes introduced into crops can allow
salt tolerance

19.  Several halophiles produce extracellular polysaccharides that have
applications as gelling agents, emulsifiers and also in microbially
enhanced oil recovery.
 Certain enzymes like amylases from halophiles that are stable at high
temperature and in benzene, toulene and chloroform are of potential
intrest.
 Halophiles produce stable enzymes like DNAases, lipases, amylases,
gelatinases and proteases capable of functioning under conditions that
lead to precipitation or denaturation of most of the protiens and can
thus have biotechnological applications.
 Bacteriorhodopsins from halophiles are used in holographic storage,
construction of bioelectronic elements of computers and information
proecessing units, nanotechnology applications such as construction of
molecular sensors.