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Table 2. Cell growth, emulsification index, surface tension, culture viscosity and biomulsifier production of the isolates in MS medium
XS1
XS2
XS3
Gram Staining
+a
+
+
Shape of cell
Short rods
Rods
Rods
Oxygen requirements
A/AN b
A/AN
A/AN
Spore formation
+
+
+
Gas/Acid from glucose
-/+
-/+
+/-
H2S form
-
-
-
Starch
-
-
+
Citrate utilization
-
-
+
Nitrate reduction
+
+
+
Hydrolysis of lipid
+
+
+
Hydrolysis of urea
-
-
+
a +, positive reaction; -, negative reaction; b A, aerobic; AN, anaerobic.
Control
XS1
XS2
XS3
O.D.600
0
2.793
2.034
2.418
Emulsification Index, %
5
52
60
50
Surface tension, mN/m
68
49
42
45
Culture viscosity, mPa.s
1.24
1.94
3.18
2.44
Bioemulsifier yield, g/L
-
2.98
4.24
3.82
Table 3. The number-average molecular weight, weight-average molecular weight and polydispersity index of the bioemulsifiers
Mn, Da
Mw, Da
PDI
Bioemulsifier produced by XS1
Peak I
362013
399812
1.104
Peak II
19596
20135
1.028
Bioemulsifier produced by XS 2
Peak I
271785
318140
1.171
Peak II
12588
13411
1.065
Bioemulsifier produced by XS 3
Peak I
526369
540468
1.027
Peak II
44106
45874
1.040
Peak III
14975
15085
1.007
Fig. 1 Phylogenetic tree of the isolates XS1, XS2 and XS3. 16S rDNA gene phylotypes and closely related sequences from NCBI database. The topology shown was obtained with the Neighbor-joining method Fig. 2 The effects of temperature, pH and salinity on microbial growth of the isolates (■, Brevibacilis sp. XS1; ▲, Geobacillus sp. XS2; ●, Geobacillus sp. XS3)
Fig. 3 The effects of temperature, pH and salinity on emulsification activity
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