Agriculture Reference
In-Depth Information
2.3. Soil Fertilization
As it was mentined earlier, sugar beet shreds are lignocellulosic residue produced during
sugar processing and as very cheap they are mainly used as animal feed or, in region with no
livestock farming, dumped in landfill. Hence, their use as a soil fertilizer has been
recommended after microbial treatment with
Aspergillus niger
in a rock phosphate-amended
medium [21, 22, 23]. Rock phosphates are natural inexpensive sources of phosphorus but
their solubilization rarely occurs in non-acidic soils. However, microbially mediated
processes involving chelation and exchange reactions are able to solubilize inorganic
phosphate forms.
A. niger
grown on sugar beet extraction waste secretes organic acids, citric
acid in particular, and this microbial conversion leads to solubilisation of rock phosphate and
transformation of the lignocellulosic material into more simple sugar compounds [21]. As a
consequence, plant growth promotion in response to
A. niger
-treated sugar beet shreds was
accompanied by increased colonization of plant root by arbuscular mycorrhizal fungi - plant
beneficial microorganisms which play a key role in soil fertility and in plant nutrient
acquisition [21, 22, 24].
Moreover, it was concluded that microbial conversion of sugar beet shreds by
A. niger
was crucial for their use as a soil fertilizer - not only it appeared to be beneficial to growth of
arbuscular mycorrhizal fungi and increase of the amount of available phosphate but it even
removed potential phytotoxic effects of the sugar beet waste [24].
One more fungus
Phanerochaete chrisosporium
was grown on mixture of sugar beet
shreds, olive wastes and rock phosphate in order to convert them to soil fertilizer [23]. The
final product was found to significantly improve growth and nitrogen and phosphate uptake
of mycorrhized plants showing high fertilizing value. Moreover, combined application of
arbuscular mycorrhizal fungus and microbially treated wastes and partially solubilized rock
phosphate exerted biocontrol functions on pathogenic
Fusarium oxysporum
by the action of
produced manganese peroxidase as natural biocide. Thus, microbial conversion of sugar beet
shreds by
Phanerochaete chrisosporium
to value-added product, besides soil fertilizing
feature, can offer an environmentally safe alternative to chemical fungicide application.
2.4. Enzyme Production
Considering that sugar beet shreds containe cellulose, hemicellulose and pectin, they
could be an excellent substrate for the microbial conversion into valuable products of
biotechnology - enzymes degrading these polymeric carbohydrates.
The possibility of conversion of polysaccharides from sugar beet waste by mixed
bacterial culture under anaerobic conditions was investigated in order to find appropriate
conditions for obtaining high levels of enzyme activities [25]. Sequential model of enzymes
production was discovered with the arabanase activity that was maximal at the early
fermentation stage and pectinases and cellulases that were produced distinctly later.
Microbial conversion of sugar beet shreds into enzymes might be very efficient by fungi,
too. The genome of the coprophilous fungus
Podospora anserina
harbors a large and highly
diverse set of putative lignocellulose-acting enzymes. Sugar beet shreds were the substrate
that induced secretion of large and broad array of different enzymatic activities degrading
carbohydrates by fungus. So,
P. anserina
showed the best performing of its secretome on
