Mechanism of Phosphate Solubilization and Physiological Functions of Phosphate-Solubilizing Microorganisms - Phosphate Solubilizing Microorganisms - page 35

Table 2.3 Some examples of organic acids produced by P-solubilizing fungi
Organism Predominant acids References

Aspergillus niger FS1, Penicillium
canescens FS23, Eupenicillium
ludwigii FS27, Penicillium
islandicum FS30

Citric, gluconic, oxalic Mendes

et al. ( 2013 )

Aspergillus awamori S19 Oxalic, malic, citric, succinic,

fumaric

Jain et al. ( 2012 )

T. flavus , T. helicus ,
P. purpurogenum , P. janthinellum

Acetic, butyric, citric, fumaric,
gluconic, glucuronic, lactic,
oxalic, propionic, succinic,
valeric

Scervino
et al. ( 2010a , b )

Aspergillus niger , Penicillium
bilaiae , Penicillium sp .

Oxalic, citric Arwidsson

et al. ( 2010 )

Aspergillus flavus , A. candidus ,
A. niger , A. terreus , A. wentii ,
Fusarium oxysporum , Penicillium
sp., Trichoderma isridae ,
Trichoderma sp.

Lactic, maleic, malic, acetic, tartaric,
citric, fumaric, gluconic

Akintokun
et al. ( 2007 )

A. flavus , A. candidus , Penicillium
oxalicum

Glutaric, malic, gluconic, oxalic Shin et al. ( 2006 )

Aspergillus flavus , A. niger ,
P. canescens

Oxalic, citric, gluconic, succinic Maliha et al. ( 2004 )

Penicillium rugulosum Citric, gluconic Reyes et al. ( 2001 )

A. niger Succinic Vazquez

et al. ( 2000 )

efficiency of solubilization, however, depends on the kind of organic acids released
into the medium and their concentration. Furthermore, the quality of the acid is
more important for P-solubilization than the total amount of acids produced by
phosphate solubilizing (PS) organisms (Scervino et al. 2010a , b ). Additionally, the
simultaneous production of different organic acids by the PS strains may contribute
to the greater potential for solubilization of insoluble inorganic phosphates (Marra
et al. 2012 ).
There are also reports which suggest that insoluble P could be transformed into
soluble forms of P without OA production by microbes (Asea et al. 1988 ; Illmer and
Schinner 1992 ; Chen et al. 2006 ). For example, Altomare et al. ( 1999 ) while
investigating the P-solubilizing ability of plant growth-promoting and biocontrol
fungus Trichoderma harzianum T-22 did not produce OA under in vitro condition
suggesting that the insoluble P could be solubilized by mechanisms other than
acidification process also. The fungal-solubilizing activity was credited both to
chelation and to reduction processes, which may be useful in the management of
phytopathogens. Apart from the OA theory, some of the inorganic acids (Reyes
et al. 2001 ; Richardson 2001 ) such as HCl (Kim et al. 1997 ), nitric acid and
sulphuric acids (Dugan and Lundgren 1965 ) produced by chemoautotrophs and
the H + pump, for example, in Penicillium rugulosum , have also been reported to
solubilize the insoluble P (Reyes et al. 1999 ). The inorganic acids so released