halophiles are the microorganisms that capable of living under salt conditions, generally many microbes are susceptible to higher salt concentration whereas these microbes tolerate higher salinity

2. Current trends and future prospects in
utilization of halophilic microorganisms
in agriculture
By
YALAVARTHI NAGARAJU, Ph.D (Ag) Scholar

3. Astronomically saline environments in the world
Dead sea
Great salt lake
Solar lake Lake Retba

4. Introduction
• Oceans salt content varies between 2-5 %
• Dead sea salt content is 31.5 %
• Saline soil, contains high amount of soluble salts
Ca2+, Mg2+, K+ and Na+ salt of Cl-, NO3-, SO4
2- and
CO3
3- etc
• Sodic soil, dominated by Na+ salt
• Saline-sodic soil that have high salt of Ca2+, Mg2+ and
K+ as well as Na+

5. Definition
• United States Department of Agriculture (USDA) (1954)
define salt affected soil as
“Saline, when EC is higher than 4 dS m-1, and Salt
Accumulation Ratio (SAR) and Exchangeable Sodium
Percentage (ESP) are less than 13 and 15; saline-sodic when
EC is greater than 4 dS m-1, and SAR and ESP are greater
than 13 and 15; and when EC is less than 4 dS m-1, SAR and
ESP greater than 13 and 15, the soil is sodic”

6. Classification
• Primary salinity: natural accumulation of salt in soil and
water by the weathering of rocks, wind borne salts deposition
• Secondary salinity: Excessive irrigation, inadequate drainage
and land clearing are the reasons for secondary salinity

7. Human activities that enhanced
salinization in soils
Deforestation
Construction of reservoirs
Salt farming
Irrigation using saline water
Erosion

8. Extent of distribution of salt affected soils in the
world

12. Statistics
• In the world, it has been estimated that around 952.2 mha of
land (7 % of total land area, nearly 33 % of arable land)
• In India, the salt affected soils account for 6.727 mha (2.1 %)
of geographical area
Percentage of saline soils in
the world
Normal soils
Saline soils

20. Secondary
Organic
Aerosol
(SOA)

21. VOC composition and hygroscopicity
parameter k

23. • Degradation of soil structure,
• Deflocculation,
• Prevalence of anaerobic
conditions,
• Increase in osmotic pressure at
the same time water potential
decreases and
• Soil crusting,
Fig 1: Deflocculation
Fig 2: Soil crusting
Detrimental effects of salts on soils

24. Detrimental effects of salts on plants

25. Detrimental effects of salts on microorganisms
• Reduction in the populations of
bacteria, fungi and actinomycetes
as the concentration of salts
increases
• Reduction in the genetic diversity of
microorganisms
• Soil respiration decreases with
increase in salts
• Microbial biomass is greatest
because dispersion of soil particles
lead to the more substrates
availability

26. Adaptations of microorganisms for salinity
• Several molecular approaches to saline adaptation have been
discovered in bacteria, including the
1.Accumulation of compatible solutes (e.g. betaine, ectoine,
glutamate, trehalose, and proline),
2. Potassium uptake (Trk, Ktr, and Kdp are three major systems
of potassium uptake in bacteria), and
3. Sodium effluxion

31. Total number of genes identified: 3807

32. Fig: Up regulation of flagella genes at 20 % NaCl
Fig: Total number of
Differentially expressed
genes identified are 614

33. Fig: Growth of wild type and 16 mutant type at 5 % and 15 % NaCl

38. Classification of microorganisms based on
salinity tolerance
Classification:
1. Non-tolerant, those which tolerate only a small concentration of
salt (about 1% w/v)
2. Slightly tolerant, tolerating up to 6-8%
3. Moderately tolerant, up to 18-20%
4. Extremely tolerant, those microbes that grow over the whole range
of salt concentrations from zero up to saturation (Larsen, 1986)
Halophiles
Non tolerant
Slightly
tolerant
Moderately
tolerant
Extremely
tolerant

39. Dunaliella sp.
Dunaliella salina
Dunaliella salina
Halococcus sp.
Haloferax sp.
Haloferax volcanii
Salinibacter sp.
Tetragenococcus muriaticus
Wallemia sp.

40. Classification plants based on salinity
tolerance
A) Halophytes- few plants
1) Accumulate salts and carry through the xylem stream and
precipitate in the leaves
2) Some species have evolved with specalized cells called salt
glands in shoots to excrete salts on its surface which is then
removed by wind or water
B) Glycophytes (sensitive to salt)- Most of the crop plants
1) Exclude salts, delaying salt stress

41. Salt stress alleviation by microbes in plants
• EPS production
• Reducing the Na+ and Cl- accumulation in leaves (Lugtenberg et
al., 2013)
• Efflux of Cl- and Na+
• Rhizosphere pH changes (Organic acid production)
• Production of ACC deaminase that controls the ethylene production
• Activation of high affinity K+ transporters
• ROS scavenging activities
• Up-regulation of salt tolerance genes
• Down regulation of ABA producing genes
• VOCs production

42. Salt stress
alleviation
mechanisms
EPS
production
Reduce the
accumulation
of Na and Cl
in leaves
Efflux of Cl
and Na from
cells
pH change in
the rhizosphere
by production
of organic acids
ACC
deaminase
productionActivation
of High
affinity K
pumping
transporters
ROS
scavenging
activity
Up regulation
of salt tolerant
genes
VOC
production
Production of
compatible
solutes

43. Mechanisms of plant growth promotion by
halophilic bacteria
• N2 fixation
• Increase mineral nutrient
exchange
• Microbial induced nutrient
cycling (Mineralization)
• Metal chelation
• Production of IAA

44. EPS production
•Microbial EPS can enhance
the aggregation of soil
particles and benefit plants by
maintaining the moisture of
the environment and trapping
nutrients
•In addition, EPS have unique
characteristics, such as
biocompatibility, gelling, and
thickening capabilities, with
industrial applications

45. ACC deaminase production

46. Nodulation enhancement by Halophiles
• Nod Factors (NFs) act as stress responsive signals in legumes
• NFs synthesis can be modulated by other PGP bacteria
• Inoculation of Soybean with salt tolarant IAA producing
Azospirillum brasiliensis along with Bradyrhizobium
japonicum enhanced the nodulation
• IAA enhanced the root branching and flavonoid synthesis
• Sea water contains approximately 0.5 ppm nitrogen
• River water contains approximately 0.25 ppm nitrogen

47. Mechanisms of plant growth promotion by AMF
• Enhancing nutrient acquisition (Al-
Karaki and Al-Raddad, 1997),
• Producing plant growth hormones,
• Improving rhizospheric and soil
conditions (Lindermann, 1994),
• Altering the physiological and
biochemical properties of the host
(Smith and Read, 1995) and
• Defending roots against soil-borne
pathogens (Dehne, 1982)
• In addition, AMF can improve host
physiological processes like water
absorption capacity of plants by
increasing root hydraulic
conductivity and favorably adjusting
the osmotic balance and composition
of carbohydrates (Rosendahl and
Rosendahl, 1991)

57. Questioner session