Environmental Engineering Reference
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nathan showed that an enzyme that hydrolysed
only phytate was present in culture filtrates of
Bacillus subtilis
(Powar and Jagannathan
1982
).
Nayini and Markakis (
1984
) first reported the
extraction of phytase from baker's yeast,
Sac-
charomyces cerevisiae,
and performed charac-
terisation and purification studies. The first com-
mercial phytase was prepared by fermentation of
a genetically modified
A. niger
strain in 1991 by
Gist-Brocades and marketed by BASF in Europe
under the brand name Natuphos
TM
(Haefner et al.
2005
). Ever since, the commercial application
and the research on phytase developed a sym-
biotic relationship and became an increasingly
important area of interest. To date, only a hand-
ful of commercial phytase products are available
(Haefner et al.
2005
).
produces more phytase activity in liquid culture
than any other naturally occurring organism.
Numerous studies have documented on other
phytase producing fungi, however, they yielded
lower phytase activity. The genus
Aspergillus
(
A. niger
in particular) continues to be preferred
for production of phytase, other enzymes and
organic acids. The reason behind this preference
is generally recognised as safe (GRAS) status,
its great secretory potential and the in-depth
knowledge with respect to growth cultivation
(Shivanna and Govindarajulu
2009
). Two pH op-
tima, at 2.5 and 5.0-5.5, can be observed for the
A. niger
NRRL 3135 phytase, phy-A (Wodzinski
and Ullah
1996
; Dvor￡kov￡
1998
). Only one pH
optimum has been noted for the pH 2.5 optimum
acid phosphatase, which has been referred to as
phy-B phytase (Ehrlich et al.
1993
).
Phytases from
Aspergillus
species usually ex-
hibit optimum temperature between 50 and 65 ﾰC
(Vats and Banerjee
2004
).
A. niger
phytase (EC
3.1.3.8) has been well characterised by Ullah and
Gibson (
1987
) and reported as an extracellular
glycoprotein with the mass of 85 kDa.
A. niger
phy-B phytase has also received attention from
enzymologists and protein chemists because of
its high catalytic activity and enhanced thermal
stability (Ullah et al.
2008
). However, restric-
tive and narrow pH optima limit its use in animal
feed industries or enzyme producers (Ullah et al.
2008
). The production of phytase from this fun-
gus has been achieved by three different cultiva-
tion methods, i.e. solid state (Ebune et al.
1995
),
semisolid (Han et al.
1987
) and submerged fer-
mentation (Howson and Davis
1983
; Vats and
Banerjee
2004
). Due to acid tolerance and high
yield (Kim et al.
1998
) fungal phytases are wide-
ly used as an animal feed additive in comparison
with bacterial phytases (Soni and Khire
2007
).
7.4.1
Sources of Phytase
Phytases occur widely among plants, animals
and microorganisms. Microbial sources of phy-
tase are widespread and can be found in soils,
aquatic systems and animals. In the last 15 years,
research has indicated that several strains of bac-
teria, yeast and fungi can produce high yields of
phytase with application at the industrial scale.
With this objective in mind, scientists started to
purify and express phytase in a wide range of
hosts using various biochemical methods. De-
pending on the source and/or expression host,
phytases can present different biophysical and
biochemical properties (Rao et al.
2009
).
1.
Fungal phytases
One of the first systematic studies on fungal
phytase was reported by Shieh and Ware (
1968
),
where various microorganisms where tested for
extracellular phytase production and a strain of
A. niger
known as
Aspergillus ficuum
NRRL
3135 was identified as the most efficient. This
strain exhibited highest phytase activity with-
out sporulation which is a prerequisite in large
scale production. Wodzinski and Ullah (
1996
)
reviewed production and activity of
A. ficuum
NRRL 3135 and observed that the selected strain
2.
Yeast phytases
Yeasts are ideal candidates for phytase and phos-
phatase research due to their mostly nonpatho-
genic and GRAS status; however, they have not
been utilised to their full potential (Satyanaraya-
na and Kunze
2009
). To date, only a few studies
have been published on yeast phytase, such as
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