''Rhodospirillum rubrum'' (''R. rubrum'') is a

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

, pink-coloured

bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...

, with a size of 0.8-1

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

. It is a

facultative anaerobe A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

with a large set of possible metabolisms depending on the conditions of its environment. It's capable of using oxygen for aerobic respiration under aerobic conditions, or an alternative terminal electron acceptor for anaerobic respiration under anaerobic conditions. Alternative terminal electron acceptors for ''R. rubrum'' include

dimethyl sulfoxide Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula . This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is ...

or trimethylamine oxide. Under aerobic growth

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

is genetically suppressed and ''R. rubrum'' is then colorless. After the exhaustion of oxygen, ''R. rubrum'' immediately starts the production of photosynthesis apparatus including membrane proteins, bacteriochlorophylls and

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

s, i.e. the bacterium becomes photosynthesis active. The repression mechanism for the photosynthesis is poorly understood. The photosynthesis of ''R. rubrum'' differs from that of plants as it possesses not

chlorophyll a } Chlorophyll ''a'' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...

, but bacteriochlorophylls. While bacteriochlorophyll can absorb light up to a maximum wavelength of 800 to 925 nm, chlorophyll absorbs light having a maximum wavelength of 660 to 680 nm. ''R. rubrum'' is a spiral-shaped bacterium (spirillum, plural form: spirilla). ''R. rubrum'' is also a nitrogen fixing bacterium, i.e., it can express and regulate

nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...

, a protein complex that can catalyse the conversion of atmospheric

dinitrogen Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh ...

into ammonia. When the bacteria are exposed to ammonia, darkness, and phenazine methosulfate, nitrogen fixation stops. Due to this important property, ''R. rubrum'' has been the test subject of many different groups, so as to understand the complex regulatory schemes required for this reaction to occur. It was in ''R. rubrum'' that, for the first time,

post-translational regulation Post-translational regulation refers to the control of the levels of active protein. There are several forms. It is performed either by means of reversible events ( posttranslational modifications, such as phosphorylation In biochemistry, p ...

of nitrogenase was demonstrated. Nitrogenase is modified by an ADP-ribosylation in the

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

residue 101 (Arg101) in response to the so-called "switch-off" effectors -

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

- and darkness. ''R. rubrum'' has several potential uses in

biotechnology Biotechnology is a multidisciplinary field that involves the integration of natural sciences and Engineering Science, engineering sciences in order to achieve the application of organisms and parts thereof for products and services. Specialists ...

: * Quantitative accumulation of PHB (polyhydroxybutyrate) precursors in the cell for the production of

bioplastic Bioplastics are plastic materials produced from renewable biomass sources. Timeline of plastic development, Historically, bioplastics made from natural materials like shellac or Celluloid, cellulose had been the first plastics. Since the end of ...

. * Production of biological

hydrogen fuel The hydrogen economy is an umbrella term for the roles hydrogen can play alongside low-carbon electricity to reduce emissions of greenhouse gases. The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not avail ...

. * Model system for studying the conversion from

light energy In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic and gravitational radiation. As energy, its SI unit is the joule (J). The quantity of radiant energy may be calculated by integrating radian ...

chemical energy Chemical energy is the energy of chemical substances that is released when the substances undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (20 ...

and regulatory pathways of the

nitrogen fixation Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

system.

References

External links

Type strain of ''Rhodospirillum rubrum'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Authority control Rhodospirillales Phototrophic bacteria Bacteria described in 1887