International Journal of Aquaculture, 2017, Vol.7, No.23, 143-158
148
Table 1 Log viable counts (LVC g
-1
GI tract) of autochthonous bacteria and yeasts isolated from the proximal intestine (PI) and distal
intestine (DI) of tilapia (
Oreochromis niloticus
)
PI
DI
Total Heterotrophic Count in YPD plate for yeast
3.85
4.17
Total Heterotrophic Count for bacteria
5.83
6.18
Amylolytic bacteria
4.24
4.87
Proteolytic bacteria
4.81
5.36
Lipolytic bacteria
3.02
3.75
Cellulolytic bacteria
3.76
4.11
Phytate degrading bacteria
2.94
3.25
Xylanolytic bacteria
3.1
3.56
Table 2 Qualitative extracellular enzyme activity of some microbial strains isolated from the GI tracts of tilapia (
Oreochromis
niloticus
). Enzyme activities were presented as scores as described in the text
Enzyme activity (U)
Strains
Amylase
1
Protease
2
Lipase
3
Cellulase
4
Phytase
5
Xylanase
6
Total score
Bacterial strains
Proximal Intestine
ONF4L
3
4
5
4
5
1
22
ONF1X
5
3
5
5
5
1
24
ONF1P
5
5
5
5
5
2
27
ONF1T
5
3
5
4
4
0
21
Distal Intestine
ONH1Ph
3
4
4
3
2
1
17
ONH1A
2
4
4
5
3
0
18
ONH2A
3
3
4
3
3
2
18
ONH2Ph
4
4
4
3
3
0
18
ONH1C
5
3
5
5
3
0
21
ONH2C
4
4
4
5
0
2
19
Yeast strains
Proximal Intestine
ONF7.1C
3
4
3
3
1
2
16
ONF8.1A
2
3
3
3
-
3
14
ONF14.1C
2
3
2
3
1
2
13
ONF21.1B
3
2
3
-
1
2
11
Distal Intestine
ONH15.1B
3
3
3
2
-
-
11
Note: With pure culture of isolates. Three replicates for each experimental set.
1
On starch (SA) plate;
2
On peptone-gelatin plate;
3
On tributyrin-agar (TA) plate;
4
On carboxy-methylcellulose (CMC) plate;
5
On sodium-phytate plate;
6
On xylan plate.
Quantitative assay of enzymes portrayed that both amylase and protease activities were the highest in ONF1P
(191.46 ± 4.05U and 64.55 ± 2.39U respectively), isolated from the PI of Nile tilapia. Considerable lipase
producing ability was exhibited by all of the 10 primarily selected bacterial isolates. Maximum lipase activity was
recorded with the strain ONF4L isolated from the PI region (4.02 ±0.14U), which was followed by ONF1P (3.99
±0.07U). The strain ONF1P also showed maximum cellulose, phytase and xylanase activities (53.33 ±2.21U,
51.11 ±1.63U and 8.69 ±0.75U, respectively). In contrast, minimum xylanase activity was noticed with the strain
ONH1Ph (2.88 ±0.06U). Overall examination of the six different extracellular enzyme activities revealed that the
strain ONF1P was the most efficient among the 10 primarily selected bacterial strains.
Among the yeasts, maximum activities for 5 out of the 6 tested exo-enzymes were recorded with the strain
ONF7.1C isolated from the PI region of
Oreochromis niloticus
. The strain ONF7.1C revealed maximum amylase
(135.13±3.26U), protease (33.42±1.87U), lipase (3.58±0.05U) and cellulase (39.87±2.14U) activities. ONF7.1C
