Random Selection Of Microorganisms ; 5 Rhodospirillum rubrum - spiral shaped spirilla

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To the Series of Random Selection of organisms By Concept of Microbiology 

We are cone with new Organism
Known as Rhodospirillum rubrum which is spiral shape spirilla.

So , 

Lets Dive in Ocean of Knowledge and Explore the what we have with Concept of Microbiology ....

1)Rhodospirillum rubrum : 

Rhodospirillum rubrum (R. rubrum) is a Gram-negative, pink-coloured Proteobacterium, with a size of 800 to 1000 nanometers. It is a facultative anaerobe, thus 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 or trimethylamine oxide.

Under aerobic growth photosynthesis 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 carotenoids, 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, 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, a protein complex that can catalyse the conversion of atmospheric dinitrogen 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 of nitrogenase was demonstrated. Nitrogenase is modified by an ADP-ribosylation in the arginine residue 101 (Arg101) in response to the so-called "switch-off" effectors - glutamine or ammonia - and darkness.

R. rubrum has several potential uses in biotechnology:

Classifications :

Kingdom    : Bacteria
Phylum       : Proteobacteria
Class          : Alphaproteobacteria
Order          : Rhodospirillales
Family        : Rhodospirillaceae
Genus        :  Rhodospirillum

Species      : R.rubrum


Introduction : 

Rhodospirillum rubrum is a Gram-negative, mesophilicproteobacteria. Its optimal growth temperature is 25-30 degrees Celsius. It has multi-layered outer envelopes, which contain mostly unsaturated, but some saturated fats in its cell wall. R. rubrum is a spirilla, meaning it has a spiral-shape. It is polarly flagellated, and therefore motile. Its length is 3-10 um, with a width of 0.8-1.0 um.

R. rubrum is a facultative anaerobe. Depending on the presence of oxygen, it can undergo alcoholic fermentation or aerobic respiration. It also is capable of photosynthesis and contains carotenoid and bateriochlorophyll in its chromatophore particles.

 These molecules help to absorb light and convert it to energy and also give it its distinct purple-red color under anaerobic conditions. R. rubrum is colorless under aerobic conditions.
Although photosynthesis is active under aerobic conditions, it is generally suppressed in the presence of O2. Sulfur is a major byproduct of photosynthesis, not O2. R. rubrum can grow heterotrophically or autotrophically when photosynthetic. 

Unlike many plants, R. rubrum contains no chlorophyll a (absorption spectra 430-662 nm). However, it does contain chlorophyll b (absorption spectra 660-680 nm) and bacteriochlorophylls (800-925 nm). This allows it to utilize more energy from the electromagnetic spectra. R. rubrum also oxidizes carbon monoxide (CO) with hydrogen gas as the pathway’s end product, and can use sulfide at low concentrations as an electron donor in carbon dioxide reduction. Additionally, it is a nitrogen fixing bacteria; it uses nitrogenase to convert atmospheric nitrogen gas to ammonia (Munk et al, 2011)

There are several applications of R. rubrum in the field of biotechnology. It is a model system of light to chemical energy conversion and for its nitrogen fixing pathways. It is also the subject of radiation resistance studies. It can be used in several ways for consumption, as well. The proteobacteria may be a source of animal food and agricultural fertilizer.

Another important role in research includes the production of vitamins. It is also being researched for its production of biological plastic from precursors of poly-hydroxy-butric-acid. R. rubrum may also be a contributor in biological hydrogen fuels, mainly through its evolution of the enzyme nitrogenase.

Ecology : 

Due to the fact that Rhodospirillum rubrum can grow both aerobically and anaerobically, it is capable of inhabiting a wide variety of conditions. 

R. rubrum is found in many natural aquatic environments such as ponds, lakes, streams, and standing water (Reslewic et. al, 2005).
 R. rubrum is also often found in mud and sewage (Brock et al, 2000). 

Studies have shown that R. rubrum can make large changes in its chemical composition to adapt to different environments (Cohen-Bazire and Kunisawa, 1963). 

R. rubrum prefers to grow in habitats with a pH of 6.8-7.2 (Bergey and Holt, 1994). 

Studies have also shown that R. rubrum has an optimal growth temperature of 22-35 degrees Celcius (Weaver, 1971).

Cell Structures & Metabolism : 

R. rubrum is a versatile organism that can obtain energy through a variety of mechanisms. Respiration and photosynthetic mechanisms exist together and their activity depends upon the presence of light and energy. R. rubrum can grow in dark chemo-tropical environments with the presence of oxygen or can grow in a photo tropical environment without oxygen.

Photosynthesis in R. rubrum begins with the donation of a hydrogen from an organic substrate to an oxidizing substrance. Bacteriochlorophyll and cartenoids, the photoreactive pigments found in the cell membrane, are bound to chromatophores (Schachman, Pardee and Stanier, 1952). 

Chromatophores are flattened disks that contain choline phospholipids, cardio lipin and galactosyl diglycerides (Benson, Wintermans, and Wiser, 1959; Benson 1961). 

Additionally, chromatophores contain a complete electron transport chain that includes various cytochromes, flavin and pyridine nucleotides (Newton and Newton, 1957; Hulcher and Conti, 1960; Kamen, 1961). The cell membrane also contains machinery for ATP synthesis, including an ATP synthetase.

In the presence of oxygen, R. rubrum is able to aerobically respire using a traditional electron transport chain with NAD+/NADH as the primary electron carrier (Keister and Minton, 1969). Among the electron transport proteins is cytochrome C428 (Chance and Smith, 1955). Aerobic respiration, however, is inhibited by photosynthesis (Oelze and Weaver, 1971).

R. rubrum is also capable of anaerobic respiration. Its non-oxygenic terminal electron acceptors can include dimethyl sulfoxide and trimethylamine oxide.

 The presence of these electron acceptors makes it possible for substrates such as succinate, malate and acetate to support growth of R. rubrum. These acceptors, however, are only approximately 33-41% as efficient as oxygen in terms of energy conservation (Schultz and Weaver, 1982).

Additionally, R. rubrum has the unique ability to oxidize carbon monoxide using carbon monoxide dehydrogenase. This oxidation pathway ends with the reduction and hydrogen and the production of hydrogen gas.

Without a terminal electron acceptor, R. rubrum completes mixed acid fermentation. The major products of pyruvate fermentation are acetate, formate, carbon dioxide and hydrogen. In the presence of bicarbonate ion, fructose is able to be fermented. The end products of this pathway are the same as that for pyruvate but with the addition of succinate and propionate (Schultz and Weaver 1982).

Besides having the ability to fix carbon dioxide (Schon and Biedermann, 1972), an identifying anabolic property of R. rubrum is its ability to fix nitrogen. Under dark conditions with the presence of fructose, R. rubrum uses nitrogenase to fix nitrogen gas to ammonium. It contains both Fe-Mo and Fe-only nitrogenases.

Pathogenicity :

Antibiotic Resistance :

Triclosan (TCS) is a broad-spectrum antimicrobial biocide that is incorporated in a multitude of contemporary personal care products due to its low toxicity in humans.

 In view of its widespread use and chemical rigidity, TCS and its derivatives have been detected in various matrices across the globe. While some bacteria, like the opportunistic pathogen Pseudomonas aeruginosa PAO1, possess innate high-level resistance to triclosan 

some bacterial species, such as the model species Escherichia coli, Salmonella enterica, Staphylococcus aureus, and Mycobacterium tuberculosis, can become more resistant through mutagenesis of given resistance mechanisms 

 The mechanisms of conferred TCS resistance can take various forms, including target mutation, increased target expression, induction of efflux pumps, decreased influx or membrane permeability, and TCS transformation or degradation.

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