Environmental Engineering Reference
In-Depth Information
7.5
Current Challenges and Future
Prospects
phytase addition to animal feed. A lot of research
data are required to decide the optimum dose of
dietary phytase for different species. Considering
the eutrophication of aquatic system with excess
P, development and use of a suitable phytase
(preferably a beta propeller phytase with high
activity at neutral pH and 37 ﾰC temperature) in
herbivorous fish diet is very encouraging. Inten-
sification of livestock or aquaculture farming
without considering the P discharge may threaten
the environment in long run. Therefore, develop-
ment of novel ideal phytase with required indus-
trial properties is desirable.
In addition to development of commercially
viable ideal phytase, some recent studies also
focus on expression of microbial phytase into
animal (e.g. pig) and plant roots (e.g. soybean).
It is therefore considered that development of
transgenic monogastric animals which are able to
produce phytase and hydrolyse phytate would be
of immense benefit to livestock and fish farm-
ers. Production of canola seeds with improved
phytase activity has paved the way for future
research to develop transgenic soybean, cot-
ton, sunflower and other grain and cereal plants,
which have potential uses in fish feed. These
plants with improved phytase production from
roots might have better P utilisation efficiency.
Development of genetically modified grains and
cereals with reduced phytic acid content can also
serve the purpose.
It is also important here to mention about
possible roles of microbes present in soil in P
management. Among various macronutrients for
plants, the poorly available insoluble inorganic
and organic forms of soil P to plants is reported
to be converted to a plant accessible form by P-
solubilising bacteria (PSB) in the rhizosphere
mainly by means of organic acid production. In
this regard, a few studies on addition of phytase
or phytase-producing microbes to the soil also
revealed increased P uptake by plants. Further
studies with specified target for maintaining soil
P level and decreasing fertiliser application might
be highly promising considering environmental
P pollution and increasing cost of fertilisers. In
this context, bacteria with activities like produc-
tion of organic acids to solubilise inorganic P and
The growth of the market for P to supplement
animal feed has been critical for the commercial
development of phytase enzyme. At present, phy-
tase constitutes about 20 % of the total enzyme
use in the livestock or allied sector, which is ex-
pected to increase many fold in the future due
to increasing productive research leads. Recent
trends in the market have clearly shown phytase
as an important enzyme and feed supplement.
Due to serious concerns about environmental
pollution, 22 countries have adopted the use of
phyA, produced from
A. niger
NRRL 3135, as
a feed additive. Industrial production of phytase
currently utilises the soil fungus
Aspergillus
, on
which considerable research has been conducted.
Phytases are being recognised for their beneficial
environmental role in reducing the P levels in ma-
nure and minimising the need to supplement P in
diets. Increasing the use of phytase in aquaculture
offers a tremendous opportunity in order to allow
the use of low cost plant meals. Further, contin-
ued research on lowering the production cost and
expanding its utilisation to other applications also
suggests its importance in the immediate future.
With so many beneficial effects reported so far,
the actual usefulness of such enzymes are lim-
ited due to high variation in activity of phytase
production, lack of farmer awareness regarding
their uses, cost factor, availability, nonexistence
of a single phytase with applicability in all kind
of feeds or applications, storage stability, narrow
pH and substrate specificity, dose response varia-
tion, high processing temperature susceptibility
and low enzyme production. Phytase with broad
substrate specificity is better suited for animal
nutrition purposes as it will readily liberate all
equatorial phosphate groups of phytic acid. Sev-
eral studies are being carried out for construction
of commercially viable phytase through enzyme
engineering for high specific activity and broad
substrate specificity along with thermostability.
Similarly, phytases of broad pH optima, with
suitable effectiveness for all types of fish, should
be developed. Moreover, as stated above, there is
a lack of consensus about the optimum dose of
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