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 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) complexes. Due to the shape of the flagellum, it can only rotate in a clockwise direction with a fast, slow or stop mechanism. Rhodobacter sphaeroides also has a complex genome and a versatile metabolism that cannot be found in most other microorganisms. R. 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.

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.

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.

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 energy. These processes are coupled to photosynthetic apparatus of the organism.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Rachel Larsen