Rhodobacter sphaeroides: Difference between revisions

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==Description and significance==
==Description and significance==
Rhodobacter sphaeroides is a rod-shaped bacterium that has an unusual single flagellum. Unlike other bacteria, the flagellum of R. sphaeroides is composed of a straight hook and hook-associated body (HBB) complexesDue to the shape of the flagellum, it can only rotate in a clockwise direction with a fast, slow or stop mechanism.  
<i>Rhodobacter sphaeroides</i> is a rod-shaped, gram-negative, purple non-sulfur photoheterotrophic bacterium belonging to the α-3 subclass of Proteobacteria. Like other species of <i>Rhodobacter</i>, <i>R. sphaeroides</i> is a metabolically diverse organism that is capable of many modes of growth including aerobic repiration, anaerobic anoxygenic photosynthesis, fermentation, and diazotrophic growth  (Blankenship, R. E. Madigan, M. T. and Bauer 1995).  The presence of such diverse metabolisms predicts the existence of complex regulatory mechanisms used by the organism in identifying the most efficient methods of carbon and energy utilization and conservation in a variety of environments.
Rhodobacter sphaeroides also has a complex genome and a versatile metabolism that cannot be found in most other microorganismsR. sphaeroides is a gram-negative purple nonsulfur phototrophic bacterium belonging to α-3 Proteobacteria. Like other species of Rhodobacter, it is a metabolically diverse organism able to grow in a wide range of lifestyles including aerobic, anaerobic, photosynthetic, and diazotrophic growth modes. It responds to environmental changes by undergoing both physiological and morphological adaptations.
 
R. sphaeroides is also the first organism that was found to possess multiple chromosomes. This discovery was made by Suwanto and Kaplan. Having two chromosomes gives the R. sphaeroides an advantage in adapting to various conditions.
Most notably, <i>Rhodobacter sphaeroides</i> is closely studied as a model organism for anoxygenic photosynthesis and carbon fixation.  The regulation of the genes that encode its photosynthetic machinery is well established.  Changes in oxygen tension trigger physiological and morphological adaptations including cytoplasmic membrane reconstruction(Niederman, R. A., D. E. Mallon, J. J. Langan 1976).  In fact, in the presence of blue light, the cell develops intracellular vessicles that contain the photosystemsBy increasing the number of membranes in the cell, it is able to more efficiently harness available light.
 
The interest in the photosynthetic capacity of <i>Rhodobacter sphaeroides</i> has prompted researchers to evaluate its potential for biofuel and bioplastic production.  <i>Rhodobacter sphaeroides</i> is able to produce polyhydroxybutyrate, a polymer of 3-hydroxybutyrate.  It is commonly thought to be a sink for excess reducing equivalents and carbon storage.   To researchers, however, it is a potential bioplastic.  While research tends to center on PHB production more in <i>Cupriavidus necator</i>, the potential to use light as an energy source for the production of bioplastics with <i>Rhodobacter sphaeroides</i> continues to tempt scientists.  In addition, <i>Rhodobacter sphaeroides</i> is capable of hydrogen production by way of its nitrogenase.  A large body of work exists documenting researchers' attempts to develop a strain of <i>Rhodobacter sphaeroides</i> that is able to produce hydrogen, a potential biofuel, using light as its energy source.
 
Some studies with <i>Rhodobacter sphaeroides</i> have also discussed its capacity for bioremediation.  For example, a biomass-dependent kinetics has been established for the precipitation of cadmium when it is introduced into a <i>Rhodobacter sphaeroides</i> culture (Bai 2008).
 
 
 
<i>Rhodobacter sphaeroides</i> swims by means of an a single subpolar flagellum, which allows it rotate in a counter-clockwise direction with a fast, slow or stop mechanism. It is also the first bacterium that was found to possess multiple chromosomes (Suwanto, A., and S. Kaplan. 1989).


==Genome structure==
==Genome structure==
Rhodobacter sphaeroides contains two distinct circular chromosomes, CⅠ(3,046kb) and CⅡ(914kb), and five endogenous plasmids (450kb). Thus, the total genome size is about 4,400kb and G+C content of its genome is 67.3 mol% and 65.7 mol% for CⅠ and CⅡ, respectively.  
 
It is revealed that a number of essential duplicate copies of R. sphaeroides are distributed between the two chromosomes. For example, one ribosomal RNA (rRNA) operon (rrnA) is found on CⅠ, while two rRNA operons (rrnB and rrnC) are on CⅡ. The difference between two chromosomes makes R. sphaeroides unique in its metabolic flexibility. Recent study found that CⅠ of R. sphaeroides has more coding abilities and conserved sequences than CⅡ. Since CⅡ is a rapidly evolving copy, it makes R. sphaeroides possible to grow in various conditions. In addition, genes on CⅡ encodes a various set of functions that are unusual for this photosynthetic organism—genes that are involved in proteins synthesis, amino acid biosynthesis, fatty acid metabolism, transcriptional regulation, energy metabolism, and structural components.
Rhodobacter sphaeroides contains two circular chromosomes, CI (3.19 Mb) and CII (0.94 Mb), and five endogenous plasmids A (0.11 Mb), B (0.11 Mb), C (0.11 Mb), D (0.10 Mb), E (0.04 Mb).  Thus, the total genome size is 4.6 Mb and G+C content is 67.3 mol % and 65.7 mol % for CI and CII, respectively. A number of essential genes of R. sphaeroides are distributed between the two chromosomes. For example, one ribosomal RNA (rRNA) operon (rrnA) is found on CI, while two rRNA operons (rrnB and rrnC) are on CII. CI has more evolutionarily conserved sequences than CII. It is thought that the rapid evolution of CII has contributed to the metabolic versatilty of this organism. Genes on CII encode products that are involved in protein synthesis, amino acid biosynthesis, fatty acid metabolism, transcriptional regulation, energy metabolism, and structural components.  It has been suggested that CII may have evolved either from a larger chromosome or from a plasmid.


==Cell Structure and Metabolism==
==Cell Structure and Metabolism==
As mentioned above, Rhodobacter sphaeroides is highly adaptive to various environmental conditions. In oxygenic conditions, it uses aerobic respiration for energy generation and the organism is similar to a normal gram-negative cell envelope structure. Under anoxygenic conditions, in the light or dark, R. sphaeroides respires anaerobically but, in the dark, it uses dimethyl sulfoxide (DMSO) or trimethylamine N-oxide (TMAO) as the terminal electron acceptor. Under aerobic-to-anaerobic shift conditions, R. sphaeroides changes morphologically by synthesizing the intracytoplasmic membrane (ICM) through an invagination process. The ICM possesses the photosynthetic apparatus and the structural components required for light energy capture, electron transport, and energy transduction.  
In the presence of oxygen, R. sphaeroides uses aerobic respiration for energy generation; its cytoplasmic membrane contains components of the electron transport chain and ATP synthesis machinery. Under anaerobic conditions in the light, R. sphaeroides grows via photosynthesis but; in the dark, it uses an electron transport chain terminating with dimethyl sulfoxide (DMSO)/trimethylamine N-oxide (TMAO) reductase. R. sphaeroides uses bacteriocholophyll a for its anoxygenic photosynthetic metabolism.  In the absence of molecular oxygen the inner membrane of the organism undergoes morphological changes forming the intracytoplasmic membrane (ICM). The distinct invaginations or pockets of the ICM houses the three pigment-protein complexes of the photosynthetic apparatus:  (1) the reaction center (RC) encircled by (2) the light harvesting complex I (LHI), which are surrounded by a variable number of (3) light harvesting complexes II (LHII).
 
The bacterium synthesizes metallotetrapyrroles that include bacteriochlorophyll, hemes, and corrinoids (vitamin B12). The kinds and level of these tetrapyrroles varies with the catabolic state of the organism. All are derived from 5-aminolevulinic acid, and the amount of ALA produced is equal to the amount of tetrapyrroles present in the cells.  There is variability among strains of Rhodobacter sphaeroides as to the number of ALA synthase genes presentThe first wild type strain to be sequenced, 2.4.1, has two genes, hemA and hemT.  The global regulatory proteins FnrL and PrrA control transcription of hemA in response to changes in oxygen tension.  Transcription factors required for hemT expression have not yet been identified.
R. sphaeroides is well-known for its diverse biochemical processes including metal reduction, nitrogen and carbon fixation, and also production of hydrogen as a source of energyThese processes are coupled to photosynthetic apparatus of the organism.


==Ecology==
==Ecology==
Rhodobacter sphaeroides is found in various conditions, especially in organic-rich habitat.
Rhodobacter sphaeroides is found in soil, in anoxic zones of waters, mud, sludge, and in organic-rich water habitats.


==Pathology==
==Pathology==
Line 38: Line 46:


==Application to Biotechnology==
==Application to Biotechnology==
1) Production of indole
1) Production of indole
Under anoxygenic conditions, R. sphaeroides OU5 is used to mediate production of indole and its derivatives from anthranilate. Indole is an aromatic compound that can be useful for growth and production of valuable compounds. It is used as the main commercial source of the material that benefits production of paddy crop and plant hormone.  
Under anoxygenic conditions, R. sphaeroides OU5 is used to mediate production of indole and its derivatives from anthranilate. Indole is an aromatic compound that can be useful for growth and production of valuable compounds. It is used as the main commercial source of the material that benefits production of paddy crop and plant hormone.
 
2) Production of ZnS nanoparticles
R. sphaeroides has been used to synthesize ZnS nanoparticles, 8nm in diameter.  These ZnS nanoparticles are highly sought after as industrial material in IR optical devices.  For instance, one can expect to use this high grade material in the clinical setting as biological probes in examinations.
 
3) Production of Rhodethrin
Rhodethrin can be isolated when R. sphaeroides OU5 is grown on L-tryptophan as sole source of nitrogen in the absence of oxygen.  The metabolite has phytohormonal activity and phytotoxicity against cancer cell lines and also inhibitory activity of cyclooxxygenase-2.
 
4) Extraction of carotenoids
Carotenoids are naturally occurring compounds found in photosynthetic bacteria.  Studies found that carotenoids having antioxidant activity and provitamin A function are able to inhibit various types of cancer and protect from cardiovascular disease and age-related macular degeneration.
 
 
==References==
1. Bai, H., Zhang, Z., and J. Gong. 2006. Biological Synthesis of Semiconductor Zinc Sulfide Nanoparticles by Immobilized Rhodobacter sphaeroides. Biotechnology Letters 28:1135-1139.
 
2. Blankenship, R. E. Madigan, M. T. and Bauer. 1995. Anoxygenic Photosynthetic Bacteria. Kluwer Academic Publishers 871-883.


2) Production of ZnS nanoparticles
3. Chory, J., Donohue, T. J., Varga, A. R., Staehelin, A., and S. Kaplan. 1984. Induction of the Photosynthetic Membranes of Rhodopseudomonas sphaeroides: Biochemical and Morphological Studies. Journal of  Bacteriology 159:540-554.
Because R. sphaeroides grow diverse conditions and is resistant to heavy metals, it is used to prepare ZnS nanoparticles. ZnS nanoparticle is highly industrial material in IR optical devices.


3) Production of Rhodethrin
4. Choudhary, M., Mackenzie, C., Nereng, K. S., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1994. Multiple Chromosomes in Bacteria: Structure and Function of Chromosome II of Rhodobacter sphaeroides 2.4.1. Journal of Bacteriology 176:7694-7702.
Rhodethrin can be isolated when R. sphaeroides OU5 is grown on a L-tryptophan as sole source of nitrogen in the absence of oxygen. The metabolite has phytohormonal activity and phytotoxicity against cancer cell lines and also inhibitory activity of cyclooxxygenase-2.


4) Extraction of carotenoids
5. Choudhary, M., Mackenzie, C., Nereng, K., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1997. Low-Resolution Sequencing of Rhodobacter sphaeroides 2.4.1: Chromosome II is a True Chromosome. Microbiology 143:3085-3099.
Carotenoids are naturally occurring compounds found in photosynthetic bacteria. Studies found that carotenoids having antioxidant activity and provitamin A function are able to inhibit various types of cancer and protect from cardiovascular disease and age-related macular degeneration.


==Current Research==
6. Choudhary, M., Zanhua, X., Fu, Y.X., and S. Kaplan. 2007. Genome Analysis of Three Strains of Rhodobacter sphaeroides: Evidence of Rapid Evolution of Chromosome II. Journal of Bacteriology 189:1914-1921.
1) Energy trapping in photosynthesis
Since R. sphaeroides is a photosynthetic bacterium in diverse environmental conditions, how energy flows through complexes has been an interest to researchers. The reaction center (RC) from Rhodobacter sphaeroides contains bacteriopheophytin (BPhy), bacteriochlorophyll (BChl), and bacteriochlorophyll dimer (P). The energy in the RC is transferred from BPhy via BChl to P, taking about 100 to 200 femtoseconds (fs). Researchers suggest that there might have correlated effects between proteins that result in long-lived electronic coherence in RC, allowing the energy to transfer rapidly into space. And then, energy can be trapped efficiently.  


2) Studies on optimal conditions of H2 production under photoheterotrophic condition.
7. Devi, R. N., Sasikala, C., and C.V. Ramana. 2000. Light-Dependent Transformation of Anthranilate to Indole by Rhodobacter sphaeroides OU5. Journal of Industrial Microbiology & Biotechnology 24:219-221.
Since hydrogen is expected to be an energy source in the future, researchers have made efforts to find efficient ways ofproducing hydrogen. Iron is used because it functions as a cofactor for proteins responsible for energy metabolism. Studies found that concentration of Fe2+ have a greater effect on production of hydrogen by R. sphaeroides. With increases in concentration of Fe2+, hydrogen production increases linearly, indicating they have direct relationship.


==References==
8. Dworkin, M. 2006. Volume 5 A Handbook on Biology of Bacteria: Proteobacteria: Alpha and Beta Subclass.  Springer, New York City, NY.
1. Bai, H., Zhang, Z., and J. Gong. 2006. Biological synthesis of semiconductor zinc sulfide nanoparticles by immobilized Rhodobacter sphaeroides. Biotechnol Lett. 28:1135-1139
 
9. Fales, L., L. Kryszak., and J. Zeilstra-Ryalls. 2001. Control of hemA Expression in Rhodobacter sphaeroides 2.4.1: Effect of a Transposon Insertion in the hbdA Gene. Journal of Bacteriology 183:1568–1576.
 
10. Fales, L., L. Nogaj., and J. H. Zeilstra-Ryalls. 2002. Analysis of the Upstream Sequences of the Rhodobacter sphaeroides 2.4.1 hemA Gene: In vivo Evidence for the Presence of Two Promoters that are both Regulated by fnrL. Photosynthesis Research 74:143-51.
 
11. Lee, H., Cheng, Y., G.R. Fleming. 2007. Coherence Dynamics in Photosynthesis: Protein Protection of Excitonic Coherence Science 316:1462-1465.
 
12. Mackenzie, C., J. M. Eraso, M. Choudhary, J. H. Roh, X. Zeng, P. Bruscella, A. Puskas, and S. Kaplan. 2007. Postgenomic Adventures with Rhodobacter sphaeroides.  Annual Review Microbiology 61:283307.
 
13. Niederman, R. A., D. E. Mallon, J. J. Langan. 1976. Membranes of Rhodopseudomonas sphaeroides IV. Assembly of Chromatophores in Low-Aeration Cell Suspensions. Biochimica et Biophysica Acta 440:429–447.
 
14. Parson, W. W. 2007. Long Live Electronic Coherence Science 316:1438-1439.


2. Chory, J., Donohue, T. J., Varga, A. R., Staehelin, A., and S. Kaplan. 1984. Induction of the photosynthetic membranes of Rhodopseudomonas sphaeroides: biochemical and morphological studies. J. Bacteriol. 159:540-554
15. Ranjith, N. K., Sasikala, C., and C. V. Ramana. 2007. Rhodethrin: A Novel Indole Terpenoid Ether Produced by Rhodobacter sphaeroides Has Cytotoxic and Phytohormonal Activities Biotechnology Letters 29:1399-1402.


3. Choudhary, M., Mackenzie, C., Nereng, K. S., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1994. Multiple chromosomes in bacteria: structure and function of chromosomeⅡ of Rhodobacter sphaeroides 2.4.1. J. Bacteriol. 176:7694-7702.
16. Ranson-Olson, B., D. F. Jones., T. J. Donohue., and J. H. Zeilstra-Ryalls.2006. In vitro and In vivo Analysis of the Role of PrrA in Rhodobacter sphaeroides 2.4.1 hemA gene expression. Journal of Bacteriology 188:3208-3218.


4. Choudhary, M., Mackenzie, C., Nereng, K., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1997. Low-resolution sequencing of Rhodobacter sphaeroides 2.4.1: chromosomeⅡ is a true chromosome. Microbiology. 143:3085-3099.
17. Ranson-Olson, B., and J. H. Zeilstra-Ryalls. 2008. Regulation of the Rhodobacter sphaeroides 2.4.1 hemA gene by PrrA and FnrL. Journal of Bacteriology 190:6769-78.


5. Choudhary, M., Zanhua, X., Fu, Y.X., and S. Kaplan. 2007. Genome analysis of three strains of Rhodobacter spharoides: evidence of rapid evolution of chromosomeⅡ. J. Bateriol. 189:1914-1921
18. Slovak, P. M., G. H. Wadhams, and J. P. Armitage. 2005. Localization of MreB in Rhodobacter sphaeroides under Conditions Causing Changes in Cell Shape and Membrane Structure.  Journal of Bacteriology 187: 54-64.


6. Devi, R. N., Sasikala, C., and C.V. Ramana. 2000. Light-dependent transformation of anthranilate to indole by Rhodobacter sphaeroides OU5. J. Industrial Microbiology & Biotechnol. 24:219-221.
19. Suwanto, A., and S. Kaplan. 1989. Physical and Genetic Mapping of the Rhodobacter sphaeroides 2.4.1 Genome: Genome Size, Fragment Identification, and Gene Localization. Journal of Bacteriology 171:5840-5849.


7. Lee, H., Cheng, Y., G.R. Fleming. 2007. Coherence dynamics in photosynthesis: protein protection of excitonic coherence. Science. 316:1462-1465
20. Yen, H., and C. Chiu. 2007. The Influences of Aerobic-Dark and Anaerobic-Light Cultivation on CoQ10 Production by Rhodobacter sphaeroides in the Submerged Fermenter. Enzyme and Microbial Technology 41:600-604.


8. Ranjith, N. K., Sasikala, C., and C. V. Ramana. 2007. Rhodethrin: a novel indole terpenoid ether produced by Rhodobacter sphaeroides has cytotoxic and phytohormonal activities. Biotechnol Lett. 29:1399-1402.
21. Zeilstra-Ryalls, J. H., and K. L. Schornberg. 2006. Analysis of hemF Gene Function and Expression in Rhodobacter sphaeroides 2.4.1. Journal of Bacteriology 188:801-4.


9. Suwanto, A., and S. Kaplan. 1989. Physical and  genetic mapping of the Rhodobacter sphaeroides 2.4.1 genome: genome size, fragment identification, and gene localization. J. Bacteriol. 171:5840-5849.
22. Zeilstra-Ryalls, J.H., and S. Kaplan. 2004. Oxygen Intervention in the Regulation of Gene Expression: The Photosynthetic Bacterial Paradigm. Cellular and Molecular Life Sciences 61:417-36.


10. Suwanto, A., and S. Kaplan. 1989. Physical and  genetic mapping of the Rhodobacter sphaeroides 2.4.1 genome: presence of two unique circular chromosomes. J. Bacteriol. 171:5850-5859.
23. Zhu H., et al. Effect of Ferrous Iron on Photo Heterotrophic Hydrogen Production by Rhodobacter sphaeroides. International Journal of Hydrogen Energy (2007), doi: 10.1016/j.ijhydene.2007.06.010


11. W. W. Parson. 2007. Long live electronic coherence. Science. 316:1438-1439.
24. Zhenxin, G., et al. Optimization of Carotenoid Extraction from Rhodobacter sphaeroides. LWT-Food Science and Technology (2007), doi:10.1016/j.lwt.2007.07.005


12. Zhenxin, G., et al. Optimization of carotenoids extraction from Rhodobacter sphaeroides. LWT-Food Science and Technology (2007), doi:10.1016/j.lwt.2007.07.005


13. Zhu H, et al. Effect of ferrous ion on photo heterotrophic hydrogen production by Rhodobacter sphaeroides. Int J Hydrogen Energy (2007), doi: 10.1016/j.ijhydene.2007.06.010
Edited by Maitreyee Mukherjee( maitrem@bgsu.edu ) and Yana Fedotova( yfedot@bgsu.edu ), Bowling Green State University.




Edited by Shinae Kang of [mailto:ralarsen@ucsd.edu Rachel Larsen]
Previously edited by Shinae Kang of [mailto:ralarsen@ucsd.edu Rachel Larsen]

Latest revision as of 16:42, 8 October 2016

This student page has not been curated.

A Microbial Biorealm page on the genus Rhodobacter sphaeroides

Classification

Higher order taxa

Bacteria; Proteobacteria; Alphaproteobacteria; Rhodobaterales; Rhodobacteraceae; Rhodobacter; sphaeroides

Species:

Rhodobacter sphaeroides

NCBI: Taxonomy

Description and significance

Rhodobacter sphaeroides is a rod-shaped, gram-negative, purple non-sulfur photoheterotrophic bacterium belonging to the α-3 subclass of Proteobacteria. Like other species of Rhodobacter, R. sphaeroides is a metabolically diverse organism that is capable of many modes of growth including aerobic repiration, anaerobic anoxygenic photosynthesis, fermentation, and diazotrophic growth (Blankenship, R. E. Madigan, M. T. and Bauer 1995). The presence of such diverse metabolisms predicts the existence of complex regulatory mechanisms used by the organism in identifying the most efficient methods of carbon and energy utilization and conservation in a variety of environments.

Most notably, Rhodobacter sphaeroides is closely studied as a model organism for anoxygenic photosynthesis and carbon fixation. The regulation of the genes that encode its photosynthetic machinery is well established. Changes in oxygen tension trigger physiological and morphological adaptations including cytoplasmic membrane reconstruction(Niederman, R. A., D. E. Mallon, J. J. Langan 1976). In fact, in the presence of blue light, the cell develops intracellular vessicles that contain the photosystems. By increasing the number of membranes in the cell, it is able to more efficiently harness available light.

The interest in the photosynthetic capacity of Rhodobacter sphaeroides has prompted researchers to evaluate its potential for biofuel and bioplastic production. Rhodobacter sphaeroides is able to produce polyhydroxybutyrate, a polymer of 3-hydroxybutyrate. It is commonly thought to be a sink for excess reducing equivalents and carbon storage. To researchers, however, it is a potential bioplastic. While research tends to center on PHB production more in Cupriavidus necator, the potential to use light as an energy source for the production of bioplastics with Rhodobacter sphaeroides continues to tempt scientists. In addition, Rhodobacter sphaeroides is capable of hydrogen production by way of its nitrogenase. A large body of work exists documenting researchers' attempts to develop a strain of Rhodobacter sphaeroides that is able to produce hydrogen, a potential biofuel, using light as its energy source.

Some studies with Rhodobacter sphaeroides have also discussed its capacity for bioremediation. For example, a biomass-dependent kinetics has been established for the precipitation of cadmium when it is introduced into a Rhodobacter sphaeroides culture (Bai 2008).


Rhodobacter sphaeroides swims by means of an a single subpolar flagellum, which allows it rotate in a counter-clockwise direction with a fast, slow or stop mechanism. It is also the first bacterium that was found to possess multiple chromosomes (Suwanto, A., and S. Kaplan. 1989).

Genome structure

Rhodobacter sphaeroides contains two circular chromosomes, CI (3.19 Mb) and CII (0.94 Mb), and five endogenous plasmids A (0.11 Mb), B (0.11 Mb), C (0.11 Mb), D (0.10 Mb), E (0.04 Mb). Thus, the total genome size is 4.6 Mb and G+C content is 67.3 mol % and 65.7 mol % for CI and CII, respectively. A number of essential genes of R. sphaeroides are distributed between the two chromosomes. For example, one ribosomal RNA (rRNA) operon (rrnA) is found on CI, while two rRNA operons (rrnB and rrnC) are on CII. CI has more evolutionarily conserved sequences than CII. It is thought that the rapid evolution of CII has contributed to the metabolic versatilty of this organism. Genes on CII encode products that are involved in protein synthesis, amino acid biosynthesis, fatty acid metabolism, transcriptional regulation, energy metabolism, and structural components. It has been suggested that CII may have evolved either from a larger chromosome or from a plasmid.

Cell Structure and Metabolism

In the presence of oxygen, R. sphaeroides uses aerobic respiration for energy generation; its cytoplasmic membrane contains components of the electron transport chain and ATP synthesis machinery. Under anaerobic conditions in the light, R. sphaeroides grows via photosynthesis but; in the dark, it uses an electron transport chain terminating with dimethyl sulfoxide (DMSO)/trimethylamine N-oxide (TMAO) reductase. R. sphaeroides uses bacteriocholophyll a for its anoxygenic photosynthetic metabolism. In the absence of molecular oxygen the inner membrane of the organism undergoes morphological changes forming the intracytoplasmic membrane (ICM). The distinct invaginations or pockets of the ICM houses the three pigment-protein complexes of the photosynthetic apparatus: (1) the reaction center (RC) encircled by (2) the light harvesting complex I (LHI), which are surrounded by a variable number of (3) light harvesting complexes II (LHII). The bacterium synthesizes metallotetrapyrroles that include bacteriochlorophyll, hemes, and corrinoids (vitamin B12). The kinds and level of these tetrapyrroles varies with the catabolic state of the organism. All are derived from 5-aminolevulinic acid, and the amount of ALA produced is equal to the amount of tetrapyrroles present in the cells. There is variability among strains of Rhodobacter sphaeroides as to the number of ALA synthase genes present. The first wild type strain to be sequenced, 2.4.1, has two genes, hemA and hemT. The global regulatory proteins FnrL and PrrA control transcription of hemA in response to changes in oxygen tension. Transcription factors required for hemT expression have not yet been identified.

Ecology

Rhodobacter sphaeroides is found in soil, in anoxic zones of waters, mud, sludge, and in organic-rich water habitats.

Pathology

This organism is not pathogenic.

Application to Biotechnology

1) Production of indole Under anoxygenic conditions, R. sphaeroides OU5 is used to mediate production of indole and its derivatives from anthranilate. Indole is an aromatic compound that can be useful for growth and production of valuable compounds. It is used as the main commercial source of the material that benefits production of paddy crop and plant hormone.

2) Production of ZnS nanoparticles R. sphaeroides has been used to synthesize ZnS nanoparticles, 8nm in diameter. These ZnS nanoparticles are highly sought after as industrial material in IR optical devices. For instance, one can expect to use this high grade material in the clinical setting as biological probes in examinations.

3) Production of Rhodethrin Rhodethrin can be isolated when R. sphaeroides OU5 is grown on L-tryptophan as sole source of nitrogen in the absence of oxygen. The metabolite has phytohormonal activity and phytotoxicity against cancer cell lines and also inhibitory activity of cyclooxxygenase-2.

4) Extraction of carotenoids Carotenoids are naturally occurring compounds found in photosynthetic bacteria. Studies found that carotenoids having antioxidant activity and provitamin A function are able to inhibit various types of cancer and protect from cardiovascular disease and age-related macular degeneration.


References

1. Bai, H., Zhang, Z., and J. Gong. 2006. Biological Synthesis of Semiconductor Zinc Sulfide Nanoparticles by Immobilized Rhodobacter sphaeroides. Biotechnology Letters 28:1135-1139.

2. Blankenship, R. E. Madigan, M. T. and Bauer. 1995. Anoxygenic Photosynthetic Bacteria. Kluwer Academic Publishers 871-883.

3. Chory, J., Donohue, T. J., Varga, A. R., Staehelin, A., and S. Kaplan. 1984. Induction of the Photosynthetic Membranes of Rhodopseudomonas sphaeroides: Biochemical and Morphological Studies. Journal of Bacteriology 159:540-554.

4. Choudhary, M., Mackenzie, C., Nereng, K. S., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1994. Multiple Chromosomes in Bacteria: Structure and Function of Chromosome II of Rhodobacter sphaeroides 2.4.1. Journal of Bacteriology 176:7694-7702.

5. Choudhary, M., Mackenzie, C., Nereng, K., Sodergren, E., Weinstock, G. M., and S. Kaplan. 1997. Low-Resolution Sequencing of Rhodobacter sphaeroides 2.4.1: Chromosome II is a True Chromosome. Microbiology 143:3085-3099.

6. Choudhary, M., Zanhua, X., Fu, Y.X., and S. Kaplan. 2007. Genome Analysis of Three Strains of Rhodobacter sphaeroides: Evidence of Rapid Evolution of Chromosome II. Journal of Bacteriology 189:1914-1921.

7. Devi, R. N., Sasikala, C., and C.V. Ramana. 2000. Light-Dependent Transformation of Anthranilate to Indole by Rhodobacter sphaeroides OU5. Journal of Industrial Microbiology & Biotechnology 24:219-221.

8. Dworkin, M. 2006. Volume 5 A Handbook on Biology of Bacteria: Proteobacteria: Alpha and Beta Subclass. Springer, New York City, NY.

9. Fales, L., L. Kryszak., and J. Zeilstra-Ryalls. 2001. Control of hemA Expression in Rhodobacter sphaeroides 2.4.1: Effect of a Transposon Insertion in the hbdA Gene. Journal of Bacteriology 183:1568–1576.

10. Fales, L., L. Nogaj., and J. H. Zeilstra-Ryalls. 2002. Analysis of the Upstream Sequences of the Rhodobacter sphaeroides 2.4.1 hemA Gene: In vivo Evidence for the Presence of Two Promoters that are both Regulated by fnrL. Photosynthesis Research 74:143-51.

11. Lee, H., Cheng, Y., G.R. Fleming. 2007. Coherence Dynamics in Photosynthesis: Protein Protection of Excitonic Coherence Science 316:1462-1465.

12. Mackenzie, C., J. M. Eraso, M. Choudhary, J. H. Roh, X. Zeng, P. Bruscella, A. Puskas, and S. Kaplan. 2007. Postgenomic Adventures with Rhodobacter sphaeroides. Annual Review Microbiology 61:283307.

13. Niederman, R. A., D. E. Mallon, J. J. Langan. 1976. Membranes of Rhodopseudomonas sphaeroides IV. Assembly of Chromatophores in Low-Aeration Cell Suspensions. Biochimica et Biophysica Acta 440:429–447.

14. Parson, W. W. 2007. Long Live Electronic Coherence Science 316:1438-1439.

15. Ranjith, N. K., Sasikala, C., and C. V. Ramana. 2007. Rhodethrin: A Novel Indole Terpenoid Ether Produced by Rhodobacter sphaeroides Has Cytotoxic and Phytohormonal Activities Biotechnology Letters 29:1399-1402.

16. Ranson-Olson, B., D. F. Jones., T. J. Donohue., and J. H. Zeilstra-Ryalls.2006. In vitro and In vivo Analysis of the Role of PrrA in Rhodobacter sphaeroides 2.4.1 hemA gene expression. Journal of Bacteriology 188:3208-3218.

17. Ranson-Olson, B., and J. H. Zeilstra-Ryalls. 2008. Regulation of the Rhodobacter sphaeroides 2.4.1 hemA gene by PrrA and FnrL. Journal of Bacteriology 190:6769-78.

18. Slovak, P. M., G. H. Wadhams, and J. P. Armitage. 2005. Localization of MreB in Rhodobacter sphaeroides under Conditions Causing Changes in Cell Shape and Membrane Structure. Journal of Bacteriology 187: 54-64.

19. Suwanto, A., and S. Kaplan. 1989. Physical and Genetic Mapping of the Rhodobacter sphaeroides 2.4.1 Genome: Genome Size, Fragment Identification, and Gene Localization. Journal of Bacteriology 171:5840-5849.

20. Yen, H., and C. Chiu. 2007. The Influences of Aerobic-Dark and Anaerobic-Light Cultivation on CoQ10 Production by Rhodobacter sphaeroides in the Submerged Fermenter. Enzyme and Microbial Technology 41:600-604.

21. Zeilstra-Ryalls, J. H., and K. L. Schornberg. 2006. Analysis of hemF Gene Function and Expression in Rhodobacter sphaeroides 2.4.1. Journal of Bacteriology 188:801-4.

22. Zeilstra-Ryalls, J.H., and S. Kaplan. 2004. Oxygen Intervention in the Regulation of Gene Expression: The Photosynthetic Bacterial Paradigm. Cellular and Molecular Life Sciences 61:417-36.

23. Zhu H., et al. Effect of Ferrous Iron on Photo Heterotrophic Hydrogen Production by Rhodobacter sphaeroides. International Journal of Hydrogen Energy (2007), doi: 10.1016/j.ijhydene.2007.06.010

24. Zhenxin, G., et al. Optimization of Carotenoid Extraction from Rhodobacter sphaeroides. LWT-Food Science and Technology (2007), doi:10.1016/j.lwt.2007.07.005


Edited by Maitreyee Mukherjee( maitrem@bgsu.edu ) and Yana Fedotova( yfedot@bgsu.edu ), Bowling Green State University.


Previously edited by Shinae Kang of Rachel Larsen