Agriculture Reference
In-Depth Information
the PS ability of
Bacillus
strains isolated from the rhizosphere of wheat from three
areas in arid and semi-arid regions in Algeria was assayed (Cherif-Silini
et al.
2013
). The bacterial cultures grown in NBRIP medium treated with varying
rates of salts had variable solubilization activity which decreased with gradual
increase in salinity. However, the response of
Bacillus
to salt was strain dependent
where D1 (121.84
μ
μ
g/ml) strains showed maximum P
solubilization compared to other strains. Interestingly, the strains B8 (58.8
g/ml) and D13 (112.83
μ
g/ml),
BA5 (78.7
g/ml) could solubilize more P at 2 % NaCl and
demonstrated a high solubilization capacity with concomitant drop in pH of the
medium at higher NaCl concentrations. Some of the strains like B14 (31.94
μ
g/ml),
B18 (78.54
μ
g/ml), and BA11 (88.5
μ
g/ml) produced the same
results even at 4 % NaCl.
Bacillus
sp. in other investigation has also shown
optimum P solubilization at 2.5 % salt concentration (Banerjee et al.
2010
).
On the contrary, among fungi, the P solubilization has been reported even from
2 % NaCl (Srividya et al.
2009
)in
Aspergillus niger
F7 to 10 % NaCl (Rosado
et al.
1998
); however, the activity declines with any further increase in the concen-
tration of NaCl (Johri et al.
1999
). The control treatment (without salt) showed
luxuriant growth, but the drop in pH and P solubilization was quite low. Moreover,
Zhu et al. (
2011
) have isolated a high P-solubilizing bacterium
Kushneria
sp. (YCWA18) from the sediment of a saltern. Being a halotolerant and capable
of growing on solid media at a very high (20 % w/v) NaCl concentration, the
Kushneria
sp. (YCWA18) showed a declining trend of P solubilization with
increasing rates of NaCl (Cabrera et al.
2007
). The reduction in P activity following
microbial growth in high-salt environment can thus be explained as follows: (i) salts
adversely affect the growth and cell proliferation resulting in a loss of solubilization
efficiency or (ii) chloride ions (Cl
) sequester or neutralize protons or acids
produced in the media and hence reduce the P-solubilizing activity. The decrease
in PSM population with increasing concentration of NaCl can be attributed to the
exposure of organisms to the conditions of hyper osmolarity resulting in a decrease
in their cytoplasmic water activities.
Solutes (NaCl) increase the osmolarity of the medium which in turn cause the
loss of intracellular water with a concomitant increase in the osmolarity of the
intracellular contents (Botsford
1984
). It appears likely that proteins (enzymes) and
other biological macromolecules have evolved to function only within certain
normal ranges of water activities, outside which some essential cellular functions
become impaired (Csonka
1989
). In a study, the nodule bacteria, for instance,
Rhizobium
strains, isolated from alkaline soils tolerated high salt concentrations
(up to 5 %), but 1,290 mM (7.5 %) salt was inhibitory to the growth of
Rhizobium
strains (Surange et al.
1997
). The ability of the selected PSB and PSF to grow and
solubilize TCP under salt stress has also been examined by Srinivasan et al. (
2012
).
It has been reported that after 15 days growth,
Aerococcus
sp. (strain PSBCRG1-1)
irrespective of NaCl concentrations showed maximum P solubilization compared to
other strains. The amount of Pi released increases with incubation period
irrespective of strains and salt concentrations. The percent Pi release, in general,
increased with an increase in NaCl concentration, up to 0.8 M for bacterial
μ
g/ml), BA7 (75.80
μ
g/ml), and BA12 (35.26
μ
