''Rhodobacter sphaeroides'' is a kind of purple bacterium; a group of bacteria that can obtain energy through

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. Its best growth conditions are

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

phototrophy ( photoheterotrophic and photoautotrophic) and aerobic chemoheterotrophy in the absence of light. ''R. sphaeroides'' is also able to fix nitrogen.De Universiteit van Texas over ''Rhodobacter sphaeroides''
It is remarkably metabolically diverse, as it is able to grow

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ically via fermentation and aerobic and

respiration. Such a metabolic versatility has motivated the investigation of ''R. sphaeroides'' as a microbial cell factory for biotechnological applications. ''Rhodobacter sphaeroides'' has been isolated from deep lakes and stagnant waters. ''Rhodobacter sphaeroides'' is one of the most pivotal organisms in the study of bacterial photosynthesis. It requires no unusual conditions for growth and is incredibly efficient. The regulation of its photosynthetic machinery is of great interest to researchers, as ''R. sphaeroides'' has an intricate system for sensing O₂ tensions. Also, when exposed to a reduction in the partial pressure of oxygen, ''R. sphaeroides'' develops invaginations in its cellular membrane. The photosynthetic apparatus is housed in these invaginations. These invaginations are also known as chromatophores. The genome of ''R. sphaeroides'' is also somewhat intriguing. It has two chromosomes, one of 3 Mb (CI) and one of 900 Kb (CII), and five naturally occurring plasmids. Many genes are duplicated between the two chromosomes but appear to be differentially regulated. Moreover, many of the open reading frames (ORFs) on CII seem to code for proteins of unknown function. When genes of unknown function on CII are disrupted, many types of auxotrophy result, emphasizing that the CII is not merely a truncated version of CI.

Small non-coding RNA

Bacterial small RNAs have been identified as components of many regulatory networks. Twenty sRNAs were experimentally identified in ''Rhodobacter spheroids,'' and the abundant ones were shown to be affected by

singlet oxygen Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambie ...

(¹O₂) exposure. ¹O₂ which generates photooxidative stress, is made by bacteriochlorophyll upon exposure to oxygen and light. One of the ¹O₂ induced sRNAs SorY (¹O₂ resistance RNA Y) was shown to be induced under several stress conditions and conferred resistance against ¹O₂ by affecting a metabolite transporter. SorX is the second ¹O₂ induced sRNA that counteracts oxidative stress by targeting mRNA for a transporter. It also has an impact on resistance against organic hydroperoxides. A cluster of four homologous sRNAs called CcsR for conserved CCUCCUCCC motif stress-induced RNA has been shown to play a role in photo-oxidative stress resistance as well. PcrZ (photosynthesis control RNA Z) identified in ''R. sphaeroides,'' is a ''trans''-acting sRNA which counteracts the

redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...

-dependent induction of photosynthesis genes, mediated by protein regulators.

Metabolism

''R. sphaeroides'' encodes several terminal oxidases which allow electron transfer to

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

and other electron acceptors (e.g.

DMSO Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds a ...

TMAO Trimethylamine ''N''-oxide (TMAO) is an organic compound with the formula (CH3)3NO. It is in the class of amine oxides. Although the anhydrous compound is known, trimethylamine ''N''-oxide is usually encountered as the water of crystallization, d ...

). Therefore, this microorganism can respire under oxic, micro-oxic and anoxic conditions under both light and dark conditions. Moreover, it is capable to accept a variety of carbon substrates, including C1 to C4 molecules, sugars and fatty acids. Several pathways for glucose catabolism are present in its genome, such as the Embden–Meyerhof–Parnas pathway (EMP), the Entner–Doudoroff pathway (ED) and the

Pentose phosphate pathway The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt and the HMP Shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-p ...

(PP). The ED pathway is the predominant glycolytic pathway in this microorganism, whereas the EMP pathway contributing only to a smaller extent. Variation in nutrient availability has important effects on the physiology of this bacterium. For example, decrease in oxygen tensions activates the synthesis of photosynthetic machinery (including photosystems, antenna complexes and pigments). Moreover, depletion of nitrogen in the medium triggers intracellular accumulation of

polyhydroxybutyrate Polyhydroxybutyrate (PHB) is a polyhydroxyalkanoate (PHA), a polymer belonging to the polyesters class that are of interest as bio-derived and biodegradable plastics. The poly-3-hydroxybutyrate (P3HB) form of PHB is probably the most common type ...

, a reserve polymer.

Biotechnological applications

A genome-scale metabolic model exists for this microorganism, which can be used for predicting the effect of gene manipulations on its metabolic fluxes. For facilitating genome editing in this species, a

CRISPR/Cas9 Cas9 (CRISPR associated protein 9, formerly called Cas5, Csn1, or Csx12) is a 160 kilodalton protein which plays a vital role in the immunological defense of certain bacteria against DNA viruses and plasmids, and is heavily utilized in genetic e ...

genome editing tool was developed and expanded. Moreover, partitioning of intracellular fluxes has been studied in detail, also with the help of ¹³C-glucose isotopomers. Altogether, these tools can be employed for improving ''R. sphaeroides'' as cell factory for industrial

biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used b ...

. Knowledge of the physiology of ''R. sphaeroides'' allowed the development of biotechnological processes for the production of some endogenous compounds. These are

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

and

isoprenoids The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes", ...

(e.g.

coenzyme Q10 Coenzyme Q, also known as ubiquinone and marketed as CoQ10, is a coenzyme family that is ubiquitous in animals and most bacteria (hence the name ubiquinone). In humans, the most common form is coenzyme Q10 or ubiquinone-10. It is a 1,4-ben ...

and

carotenoids Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, ...

). Moreover, this microorganism is used also for

wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...

. Hydrogen evolution occurs via the activity of the enzyme

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 fam ...

, whereas isoprenoids are synthesized naturally via the

endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, ...

MEP pathway The non-mevalonate pathway—also appearing as the mevalonate-independent pathway and the 2-''C''-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate (MEP/DOXP) pathway—is an alternative metabolic pathway for the biosynthesis of the is ...

. The native pathway has been optimized via genetic engineering for improving

synthesis. Alternatively, improvement of isoprenoid synthesis was obtained via the introduction of a

heterologous The term heterologous has several meanings in biology. Gene expression In cell biology and protein biochemistry, heterologous expression means that a protein is experimentally put into a cell that does not normally make (i.e., express) that ...

mevalonate pathway The mevalonate pathway, also known as the isoprenoid pathway or HMG-CoA reductase pathway is an essential metabolic pathway present in eukaryotes, archaea, and some bacteria. The pathway produces two five-carbon building blocks called isopenteny ...

Synthetic biology Synthetic biology (SynBio) is a multidisciplinary area of research that seeks to create new biological parts, devices, and systems, or to redesign systems that are already found in nature. It is a branch of science that encompasses a broad ran ...

-driven engineering of the metabolism of ''R. sphaeroides'', in combination to the functional replacement the

with

, allowed to further increase bioproduction of isoprenoids in this species.

Accepted name

* ''Rhodobacter sphaeroides'' (van Niel 1944) Imhoff et al., 1984

Synonyms

* ''Rhodococcus minor'' Molisch 1907 * ''Rhodococcus capsulatus'' Molisch 1907 * ''Rhodosphaera capsulata'' (Molisch) Buchanan 1918 * ''Rhodosphaera minor'' (Molisch) Bergey et al. 1923 * ''Rhodorrhagus minor'' (Molisch) Bergey et al. 1925 * ''Rhodorrhagus capsulatus'' (Molisch) Bergey et al. 1925 * ''Rhodorrhagus capsulatus'' Bergey et al. 1939 * ''Rhodopseudomonas sphaeroides'' van Niel 1944 * ''Rhodopseudomonas spheroides'' van Niel 1944 * ''Rhodorrhagus spheroides'' (van Niel) Brisou 1955

Reclassification

In 2020 it was recommended that ''Rhodobacter sphaeroides'' be moved to the genus ''Cereibacter''. This is th
name
currently used by the NCBI taxonomy database.

References

Bibliography

* Inomata Tsuyako, Higuchi Masataka (1976), ''Incorporation of tritium into cell materials of Rhodpseudomonas spheroides from tritiated water in the medium under aerobic conditions'' ; Journal of Biochemistry 80(3), p569-578, 1976-09

External links

Type strain of ''Rhodobacter sphaeroides'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q4186823 Phototrophic bacteria Rhodobacteraceae Bacteria described in 1944