1:45 PM - 3:15 PM
[O11-P96] Iron bacteria distributed around Sendai High School
Keywords:Iron bacteria, Ferrous iron, Water quality survey, SEM-EDS
1. Background and purpose of the study
Iron bacteria are organisms that use the energy obtained when converting Fe2+ to Fe3+ to carry out their life activities. They have an iron oxide shell and reproduce in places where groundwater containing a large amount of Fe2+ springs out. As they reproduce, they form an iron oxide coating similar to an oil film on the water surface, producing a reddish-brown precipitate.
We found reddish-brown precipitates and oily film-like substances in many waterside areas such as gutters and ponds around Sendai High School (Photo1), and investigated whether these were also caused by iron bacteria. In previous studies, we thought that the reddish-brown precipitates and oily film-like substances were likely substances produced by iron bacteria. However, the bodies of iron bacteria could not be confirmed, and the constituent elements of the reddish-brown precipitates and oily film-like substances were not analyzed. In this year's study, we aimed to grasp the state of iron in the survey area by conducting more detailed microscopic observations and water quality measurements, identify the type of iron bacteria, and confirm the constituent elements of the reddish-brown precipitates and oily film-like substances using SEM-EDS.
2. Experimental method
2-1 Water quality measurement Field New 4in1 ORP meter (FN006A) was used to measure the pH, redox potential, and temperature of the water.
2-2 Observe the shape characteristics of the iron bacteria with an optical microscope. To see the bacteria inside the iron oxide sheath, two drops of a solution of hydrochloric acid and water in a 1:2 ratio were dropped sideways between the preparation and the cover glass, and then observations were performed.
2-3 High-magnification observations and elemental analysis were performed using a scanning electron microscope (JSM-7001F, JSM-7000F). One or two drops of the sample were dropped onto the preparation, dried, and then vapor-deposited with osmium.
3. Results
3-1 As a result of the water quality measurement, as shown in Table 1, the pH was near neutral and the redox potential was negative.
3-2 As a result of the optical microscope observation, two types of what appeared to be iron bacteria were found. One type had a linear sheath with bacterial cells about 2 µm wide lined up (Photo2), and this type was seen in large numbers. The other type had a ribbon-like shape with a width of about 1 µm, and there were few of these.
3-3 Electron microscope observation showed that the linear sheath was about 0.8 µm to 1.2 µm thick, had a rough and uneven surface, and had holes in it. The ribbon shape was about 0.5 µm wide at its shortest point and about 1.2 µm wide at its thickest point, and had a fibrous surface. Both types had spherical lumps around them. Elemental analysis showed that they contained a lot of iron and oxygen. Photos 3 to 8 show electron microscope photos and elemental mapping diagrams of iron and oxygen.
4. Discussion
When the water quality measurement results were plotted against Eh (electric potential) and pH, they were as shown in Figure 1, and it was found that Fe2+ was dominant, making it an environment where iron bacteria could easily grow. The iron bacteria with a linear sheath at near-neutral pH that were discovered around Sendai High School this time are believed to be Leptothrix ochracea, while the ribbon-shaped iron bacteria are believed to be Gallionella ferruginea. In addition, the main components of the reddish-brown precipitate and oily film-like substance are iron and oxygen, and we believe that they are undoubtedly substances produced by iron bacteria.
5. Acknowledgements
This research was supported by the Nakatani Foundation for the Promotion of Science Education.
We borrowed an electron microscope from the Department of Earth Sciences, Graduate School of Science, Tohoku University, for the electron microscope observations. We would like to express our sincere gratitude to Professor Norihiro Nakamura and Professor Yoshinori Ito.
6. References
・1 Koike, Yoshihiro (2011) How to distinguish between oil film and iron bacteria
・2 Shimada, Shikino and Honda, Kazuhiro (2008) Observation of reddish brown precipitates caused by iron bacteria in the Aina Green Biotope
・3 Takeno, Naoto, Eh-pH diagram atlas: Comparison of thermodynamic databases
・4 Kato, Shingo (2015) Physiological morphology and biology of iron-oxidizing bacteria growing near neutral pH
・5 Japanese Industrial Standards JIS: Testing method for iron bacteria in industrial water
・6 Japanese waterworks organisms-photos and explanations-revised edition, 1993, Japan Water Works Association
・7 Environmental microorganisms encyclopedia, Kodansha Co. Ltd. (1995)
Iron bacteria are organisms that use the energy obtained when converting Fe2+ to Fe3+ to carry out their life activities. They have an iron oxide shell and reproduce in places where groundwater containing a large amount of Fe2+ springs out. As they reproduce, they form an iron oxide coating similar to an oil film on the water surface, producing a reddish-brown precipitate.
We found reddish-brown precipitates and oily film-like substances in many waterside areas such as gutters and ponds around Sendai High School (Photo1), and investigated whether these were also caused by iron bacteria. In previous studies, we thought that the reddish-brown precipitates and oily film-like substances were likely substances produced by iron bacteria. However, the bodies of iron bacteria could not be confirmed, and the constituent elements of the reddish-brown precipitates and oily film-like substances were not analyzed. In this year's study, we aimed to grasp the state of iron in the survey area by conducting more detailed microscopic observations and water quality measurements, identify the type of iron bacteria, and confirm the constituent elements of the reddish-brown precipitates and oily film-like substances using SEM-EDS.
2. Experimental method
2-1 Water quality measurement Field New 4in1 ORP meter (FN006A) was used to measure the pH, redox potential, and temperature of the water.
2-2 Observe the shape characteristics of the iron bacteria with an optical microscope. To see the bacteria inside the iron oxide sheath, two drops of a solution of hydrochloric acid and water in a 1:2 ratio were dropped sideways between the preparation and the cover glass, and then observations were performed.
2-3 High-magnification observations and elemental analysis were performed using a scanning electron microscope (JSM-7001F, JSM-7000F). One or two drops of the sample were dropped onto the preparation, dried, and then vapor-deposited with osmium.
3. Results
3-1 As a result of the water quality measurement, as shown in Table 1, the pH was near neutral and the redox potential was negative.
3-2 As a result of the optical microscope observation, two types of what appeared to be iron bacteria were found. One type had a linear sheath with bacterial cells about 2 µm wide lined up (Photo2), and this type was seen in large numbers. The other type had a ribbon-like shape with a width of about 1 µm, and there were few of these.
3-3 Electron microscope observation showed that the linear sheath was about 0.8 µm to 1.2 µm thick, had a rough and uneven surface, and had holes in it. The ribbon shape was about 0.5 µm wide at its shortest point and about 1.2 µm wide at its thickest point, and had a fibrous surface. Both types had spherical lumps around them. Elemental analysis showed that they contained a lot of iron and oxygen. Photos 3 to 8 show electron microscope photos and elemental mapping diagrams of iron and oxygen.
4. Discussion
When the water quality measurement results were plotted against Eh (electric potential) and pH, they were as shown in Figure 1, and it was found that Fe2+ was dominant, making it an environment where iron bacteria could easily grow. The iron bacteria with a linear sheath at near-neutral pH that were discovered around Sendai High School this time are believed to be Leptothrix ochracea, while the ribbon-shaped iron bacteria are believed to be Gallionella ferruginea. In addition, the main components of the reddish-brown precipitate and oily film-like substance are iron and oxygen, and we believe that they are undoubtedly substances produced by iron bacteria.
5. Acknowledgements
This research was supported by the Nakatani Foundation for the Promotion of Science Education.
We borrowed an electron microscope from the Department of Earth Sciences, Graduate School of Science, Tohoku University, for the electron microscope observations. We would like to express our sincere gratitude to Professor Norihiro Nakamura and Professor Yoshinori Ito.
6. References
・1 Koike, Yoshihiro (2011) How to distinguish between oil film and iron bacteria
・2 Shimada, Shikino and Honda, Kazuhiro (2008) Observation of reddish brown precipitates caused by iron bacteria in the Aina Green Biotope
・3 Takeno, Naoto, Eh-pH diagram atlas: Comparison of thermodynamic databases
・4 Kato, Shingo (2015) Physiological morphology and biology of iron-oxidizing bacteria growing near neutral pH
・5 Japanese Industrial Standards JIS: Testing method for iron bacteria in industrial water
・6 Japanese waterworks organisms-photos and explanations-revised edition, 1993, Japan Water Works Association
・7 Environmental microorganisms encyclopedia, Kodansha Co. Ltd. (1995)