Agriculture Reference
In-Depth Information
Fig. 3.1
Factors affecting the survival and physiological functions of PSM
acidic (Bajpai and Sundara
1971
). The phosphate-solubilizing (PS) activity of PSF
and yeast in contrast occurs best in the pH range 4-6 (Ahmad and Jha
1968
).
Moreover, the activity of PSF is considerably reduced when pH values increases to
pH 7.0 to pH 8.0 because fungi in general prefer slightly acidic conditions for
growth than do the bacterial cultures. This indeed is true because in most of the
cases, acidification has been reported as the principal mode of P solubilization by
microbes (Khan et al.
2007
,
2009
,
2010
,
2013
). Therefore, high P solubilization by
microbes is quite often associated with a consequent decrease in the pH of the
medium in which they are growing. Concomitantly, a significantly negative corre-
lation between pH and solubilization of inorganic P, for example, calcium phos-
phate, has been reported (Wani et al.
2008
). Also, a significant correlation between
final pH value and titratable acidity and between titratable acidity and soluble P has
been observed when 42 bacterial isolates were tested for their ability to solubilize
rock phosphate (RP) and Ca-P in culture medium (Nahas
1996
). Recently, the
liquid Pikovskaya (PVK) medium inoculated with PSF and PSB showed greater
reduction in pH, and it has been observed that more the phosphate solubilized, the
greater was the reduction in pH values (Reena et al.
2013
). Interestingly, both
bacteria (
P. aeruginosa
and
B. subtilis
) and fungi (
A. niger
,
Penicillium
sp., and
Micrococcus
sp.) showed maximum P solubilization at pH 3.0 at 28
C and 37
C,
respectively. Furthermore, such bacterial and fungal cultures produced carboxylic
acids, which solubilized the insoluble Tri-calcium phosphate (TCP) efficiently in
the medium. The titratable acidity also confirmed the release of carboxylic acid in
