Rhodobacter sphaeroides

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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