Agriculture Reference
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It was clearly observed that a glucose band appeared again after 3 d of culturing, which
supported the idea that the
B. licheniformis
TK3-Y strain degraded green seaweed
polysaccharides in an exolytic manner. These depolymerized products in the culture broth of
the green seaweed may contribute to plant growth because seaweed oligosaccharides have
been known to stimulate plant growth by enhancing carbon and nitrogen assimilation, basal
metabolism and cell division (Gonzalez et al., 2013). In addition, these decomposed products
might affect soil aggregation (Haslam & Hopkins, 1996).
Red Seaweed
A time course monitoring the degradation of red seaweed polysaccharides by
B.
alcalophilus
is shown in Figure 3. As shown in Figure 3A, the pH steadily increased from
7.62 to 8.40 after 5 d as the biodegradation proceeded.
The cell number increased from 6.0×10
5
CFU ml
-1
to 3.1×10
7
CFU ml
-1
after 2 d, and
then was almost maintained until the end. The concentration of reducing sugar was 0.96 g l
-1
and decreased to 0.74 g l
-1
after 1 d. Then, the concentration of reducing sugar slightly
increased to 0.77 g l
-1
after 5 d. Reducing sugars that were present at the beginning of
biodegradation were due to the
Porphyra
powder pretreatment to improve its solubility. The
drop in the concentration of reducing sugars was due to their consumption by the cells.
Oligosaccharides are a better inducer for agarase production (van der Meulen & Harder,
1976). After
B. alcalophilus
utilized the oligosaccharides, the active biodegradation of red
seaweed polysaccharides could occur after 3 d. Based on the changes in pH, cell number, and
in the concentration of reducing sugars, the 4-d culture broth was selected, and its fertilizing
ability was later tested.
Figure 3B and Figure 3C present the changes in the concentrations of cations and anions
during the degradation of red seaweed polysaccharides. As shown in Figure 3B, the
concentration of Na
+
slightly decreased from 989.0 to 955.2 mg l
-1
, whereas the concentration
of NH
4
+
increased from 59.2 to 106.3 mg l
-1
. During biodegradation, the concentrations of
anions did not change much; however, the concentrations of Cl
-
and PO
4
3-
increased, whereas
the concentrations of NO
2
-
and NO
3
-
decreased due to their partial utilization by cells. The
content of NaCl in this culture broth was not as high as that of the green seaweed culture
broth. This observation was because the initial content of NaCl in each culture medium was
quite different.
The average removal percentages of COD
Cr
and TN were 25.9 and 12.1%, respectively
(Figure 3D). The COD
Cr
/TN ratio decreased from 13.5 to 11.4 in the end such that the
microbial degradation occurred under a relatively stable C/N ratio. The C/N ratio was similar
to that (10.5-13.1) achieved in seaweed composting (Tang et al., 2011).
As red seaweed polysaccharides were degraded by
B. alcalophilus
over time, TLC
revealed the migration of degraded oligosaccharides with different DP (Figure 4). Although
the bands of DP 1-3 that were produced by the
Porphyra
powder pretreatment were observed
at the beginning of the experiments, these bands weakened over time in culture.
It was clearly observed that galactose and oligosaccharide bands appeared again after the
4 d culture, supporting the idea that the
B. alcalophilus
strain degraded red seaweed
polysaccharides. Red seaweed extract has been demonstrated to affect the growth, yield and
nutrient uptake of soybeans (Rathore et al., 2009). Accordingly, these depolymerized
products in the culture broth of the red seaweed may be good candidate compounds for plant
growth.
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