Azotobacter as a potential siderophore bacteria
Enny Zulaika, Aidtya Pamungkas, N. D. Kuswytasari, Nurhidayatul Alami, Maya Shovitri
Biology Departement of Mathematics and Natural Sciences Faculty. Institut Teknologi
Sepuluh Nopember (ITS). Kampus ITS Keputih Sukolilo-60111-Surabaya, Indonesia.
Email: [email protected]
Abstract
Iron (Fe) is one of the essential element for bacterial metabolism. Naturally, it presents abundant in the
environment, but it can be directly uptake by bacteria due to its limited solubility under aerobic
condition in the rhizosphere. Azotobacter secrete siderophore for iron chelating and make it available
since Azotobacter needs iron in a great number for fixing nitrogen. The aim of this study was to find
out whether Azotobacter which isolated from an urban farming had the ability to secrete siderophore,
as not all of Azotobacter are siderophore producer. A selective medium of Fe-CAS was used, at which
after 24 hours incubation Azotobacter colony were turning yellow to orange in contrast with the blue
background color of the selective medium. Results showed that all Azotobacter isolates were able to
secrete siderophore. Isolate with code A7 was the most strong siderophore producer, with the clear
zone diameter was 1.7 cm.
Keywords: Azotobacter, Fe, siderophore.
Introduction
Siderophore is iron chelating compound which is secreted and released out of the bacterial
cell as a response to gain iron for their metabolism (Madigan et al., 2012). Siderophores may
also be used to hide Fe in the rhizosphere so it’s not available for the growth of pathogenic
microbes (Husen, 2007). Azotobacter is one of the bacteria that secrete siderophore (Miethke
dan Marahiel, 2007). Some of the Azotobacter were isolated from ITS eco urban farming area
(Zulaika dkk, 2015). The aim of this study was to find out whether Azotobacter which
isolated from an urban farming had the ability to secrete siderophore.
Material and methods
Objects that used in this study were Azotobacter isolated from ITS eco urban farming
area, with code A1a, A1b, A2, A3, A5, A6, A7, A8, A9, and A10. Isolates were aseptically
inoculated in agar media contained Fe-CAS (Chrome Azurol S) using streak plate method and
incubated for 24 hours. Isolates that produce siderophore are characterized with yellow to
orange colony, which contrast with Fe-CAS agar media (Husen, 2007).
Result and Discussion
All isolates produced siderophore, characterized by orange siderophore zone around the
colonies (Figure 1). Siderophore zone was produced because of Fe chelation to Fe-CAS
media by siderophore that secreted by bacteria. Azotobacter will secrete siderophore when
they lack of Fe (Andrews et al., 2003).
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Figure 1. Siderophore zone produced by each isolate
Each isolates produced siderophore zone with different diameter (Table 1). Isolate A7
has the widest diameter of siderophore zone (1,75 cm) than other isolates after 48 hours
incubation. The difference of siderophore zone diameter is related to iron chelation capability
of each isolate. Bacteria that produced wider siderophore zone indicated as strong iron
chelating bacteria (Verma et al., 2012).
Isolate
code
A1a
A1b
A2
A3
A5
A6
A7
A8
A9
A10
Table 1. Azotobacter siderophore zone diameter (cm)
Secrete
Diameter after 24 h
Diameter after 48 h
siderophore
incubation
incubation
+
0,40
1,10
+
0,38
0,88
+
0,50
0,50
+
0,50
0,85
+
0,19
0,35
+
0,50
0,80
+
1,70
1,75
+
0,20
0,30
+
0,80
1,10
+
0,60
0,90
Conclusion
All Azotobacter isolates used in this study were produced siderophore. Isolate A7
produced the widest siderophore zone, with the diameter 1,75 cm after 48 hours incubation.
Bibliography
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Microorganisms Fifth Ed. San Fransisco : Pearson Education
Miethke, M dan Marahiel. Siderophore-Based Iron Acquisition and Pathogen Control. 2007.
Journal of Microbiology and Molecular Biology. 71 (3) : 413-417
Verma, V., Joshi K., dan Mazumdar, B. 2012. Study of Siderophore Formation in NoduleForming Bacterial Species. Research Journal of Chemical Sciences Vol. 2 (11): 26-29.
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