Chromatium: Difference between revisions

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=Gene transfer of dsrGenes=
=Gene transfer of dsrGenes=
The only gene region known so far to be essential for oxidation of stored sulfur was localized by interposon mutagenesis in Alc. vinosum ( Dahl et al., 2005; Pott and Dahl, 1998). A total of 15 open reading frames, designated dsrABEFHCMKLJOPNRS, were identified ( Fig. 3). The first two of these genes encode the reverse dissimilatory sulfite reductase (DsrAB) of Alc. vinosum ( Hipp et al., 1997; Schedel et al., 1979). Very similar gene clusters are also found in Hlr. halophila and GSB ( Table 3 and Fig. 3). In Hlr. halophila the dsr gene cluster in addition contains genes encoding putative regulatory proteins and proteins possibly involved in sulfate transport downstream of dsrN ( Dahl, 2008). GSB contain a cluster, dsrNCABLEFHTMKJOP, the only difference to Alc. vinosum being the absence of dsrRS and the presence of dsrT. This cluster is present in all GSB, except Chl. ferrooxidans and Chp. thalassium, and it most likely encodes the same function as in Alc. vinosum. In Cba. tepidum TLS the dsr genes are split into two clusters, and three functional dsr genes are duplicated (dsrA, dsrC, and dsrL) ( Fig. 3). This may be due to a frameshift mutation in the dsrB gene in a recent ancestor of the TLS strain that rendered the gene non-functional. This could have been selected for a duplication, rearrangement, and subsequent frameshift mutation of a small segment of the genome, which restored a functional dsrB gene but also resulted in a duplication of the dsrCABL gene cluster. The two regions that contain a dsrCABL cluster in Cba. tepidum TLS are 99.4% identical at the nucleotide level. From the currently available data, it appears that the dsr genes only occur as a single cluster in all other genome-sequenced GSB.
In several cases phylogenetic analysis of the common Dsr proteins yielded two separate clusters consisting of proteins from sulfate reducers on the one hand and of proteins from sulfur oxidizers on the other (Sander et al., 2006). Within the GSB, DsrA and other Dsr proteins constitute a monophyletic group. However, the dsr genes have experienced lateral gene transfer (LGT) within the GSB phylum; for example, DsrA from Prosthecochloris aestuarii DSMZ 271T is located within the Chlorobium/Chlorobaculum cluster ( Frigaard and Bryant, 2008a). In contrast to DsrAB sulfite reductase and other cytoplasmic Dsr proteins, the components of the membrane-bound DsrMKJOP complex of GSB do not cluster with the proteins of other sulfur oxidizers but affiliate with the sulfate-/sulfite-reducing prokaryotes. This phenomenon suggests a horizontal gene transfer, which is also supported by the presence of dsrT ( Mussmann et al., 2005) in GSB, a gene otherwise only found in sulfate-/sulfite-reducing prokaryotes ( Sander et al., 2006). The Dsr system in GSB is therefore considered to have an intriguing chimeric nature possibly generated by lateral gene transfer of dsrTMKJOP from a sulfate-reducing prokaryote to a common ancestor of GSB.


=References=
=References=

Revision as of 21:12, 11 May 2015

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Classification

Domain: Bacteria Phylum: Proteobacteria Class: Gammaproteobacteria Order: Chromatiales Family: Chromatiaceae Genus: Chromatium Species: Chromatium okenii

Description

Alt
Chromatium [F1]

Chromatium were first described by Swiss botanist, Maximilian Perty, in 1852. He introduced the genus name and called them "pigment bacteria". Theodor W. Engelmann first cultured and experimented with these bacteria to discover the light excitation of the purple bacteria in 1883.

Chromatium is a gram negative bacteria found in marine environments. They tend to be flagellated straight rod shaped or even slightly curved rods of ~1 µm in diameter and 3-4 µm long.[3] These bacteria belong to the purple photosynthetic sulfur bacteria that oxidize sulfide into sulfur which is deposited in intracellular granules in their cytoplasm.[2]

Ecology and Significance

Little is known about the photosynthetic purple sulfur bacteria They may represent one of the most primitive photosynthetic organisms that are capable of carbon fixation. Researchers hope to sequence nine type strains of purple sulfur bacteria in hopes that it will provide a better understanding of the process of photosynthesis in these organisms as well as an overall process. Genomic information will also provide insight to the intricacies of global carbon and sulfur cycles. additionally, some of these bacteria may be members of the phototrophic mats in geothermal environments, playing a key role in the microbial communities. [4]

Diversity

[5]

Chromatiaceae is closely related to Ectothiorhodospiraceae but is distinguished by its lack of lamellar intracytoplasmic membrane structures. Ectothiorhodospiraceae have a significant differences in polar lipid composition and dependence on saline and alkaline growth conditions.

There are two major physiological groups of Chromatium: metabolically versatile and metabolically specialized species.

The versatile species ( Allochromatium vinosum and Allochromatium minutissimum) use thiosulfate with elemental sulfur as electron donor. They can grow photoorganoheterotrophically in the absence of reduced sulfur compounds or as chemolithotrophs on reduced sulfur compounds.

The specialized species such as Chromatium okenii, Allochromatium warmingii, and Isochromatium budfer. These species depend on strict anaerobic conditions and are obligate phototrophs. Sulfide is required for their metabolic processes but only acetate and pyruvate are photoassimilated in the presence of CO2 and sulfide.

Metabolism

These bacteria grow photolithoautotrophically, photolithoheterotrophically, and/or photoorganogeterotrophically.

They grow in the presence of light under anaerobic conditions. They can grow on an inorganic medium using CO2 as the sole carbon source in the presence of reduced inorganic sulfur. They use sulfur and sulfide as sole photosynthetic electron donor. Purple sulfur bacteria have to fix CO2 in order to grown and survive.

Chromatium can perform anoxygenic photosynthesis and contain bacteriochlorophyll a and carotenoids of spirilloxanthin group.

Interesting: Sulfur Deposits

Gene transfer of dsrGenes

The only gene region known so far to be essential for oxidation of stored sulfur was localized by interposon mutagenesis in Alc. vinosum ( Dahl et al., 2005; Pott and Dahl, 1998). A total of 15 open reading frames, designated dsrABEFHCMKLJOPNRS, were identified ( Fig. 3). The first two of these genes encode the reverse dissimilatory sulfite reductase (DsrAB) of Alc. vinosum ( Hipp et al., 1997; Schedel et al., 1979). Very similar gene clusters are also found in Hlr. halophila and GSB ( Table 3 and Fig. 3). In Hlr. halophila the dsr gene cluster in addition contains genes encoding putative regulatory proteins and proteins possibly involved in sulfate transport downstream of dsrN ( Dahl, 2008). GSB contain a cluster, dsrNCABLEFHTMKJOP, the only difference to Alc. vinosum being the absence of dsrRS and the presence of dsrT. This cluster is present in all GSB, except Chl. ferrooxidans and Chp. thalassium, and it most likely encodes the same function as in Alc. vinosum. In Cba. tepidum TLS the dsr genes are split into two clusters, and three functional dsr genes are duplicated (dsrA, dsrC, and dsrL) ( Fig. 3). This may be due to a frameshift mutation in the dsrB gene in a recent ancestor of the TLS strain that rendered the gene non-functional. This could have been selected for a duplication, rearrangement, and subsequent frameshift mutation of a small segment of the genome, which restored a functional dsrB gene but also resulted in a duplication of the dsrCABL gene cluster. The two regions that contain a dsrCABL cluster in Cba. tepidum TLS are 99.4% identical at the nucleotide level. From the currently available data, it appears that the dsr genes only occur as a single cluster in all other genome-sequenced GSB.

In several cases phylogenetic analysis of the common Dsr proteins yielded two separate clusters consisting of proteins from sulfate reducers on the one hand and of proteins from sulfur oxidizers on the other (Sander et al., 2006). Within the GSB, DsrA and other Dsr proteins constitute a monophyletic group. However, the dsr genes have experienced lateral gene transfer (LGT) within the GSB phylum; for example, DsrA from Prosthecochloris aestuarii DSMZ 271T is located within the Chlorobium/Chlorobaculum cluster ( Frigaard and Bryant, 2008a). In contrast to DsrAB sulfite reductase and other cytoplasmic Dsr proteins, the components of the membrane-bound DsrMKJOP complex of GSB do not cluster with the proteins of other sulfur oxidizers but affiliate with the sulfate-/sulfite-reducing prokaryotes. This phenomenon suggests a horizontal gene transfer, which is also supported by the presence of dsrT ( Mussmann et al., 2005) in GSB, a gene otherwise only found in sulfate-/sulfite-reducing prokaryotes ( Sander et al., 2006). The Dsr system in GSB is therefore considered to have an intriguing chimeric nature possibly generated by lateral gene transfer of dsrTMKJOP from a sulfate-reducing prokaryote to a common ancestor of GSB.

References

[1] Golyshin, Peter N. “Genome Sequence Completed of Alcanivorax borkumensis, a Hydrocarbon-degrading Bacterium That Plays a Global Role in Oil Removal from Marine Systems.” 3 (2003): 215-20. Print.

[2] Neyra, Carlos A. Carbon Metabolism. Boca Raton, FL: CRC Pr., 1985. Web. 11 May 2015.

[3] "Bacterial Metabolism & Photosynthesis." Bacterial Photosynthesis. N.p., n.d. Web. 11 May 2015.

[4] "Why Sequence Purple Sulfur Bacteria? - DOE Joint Genome Institute." DOE Joint Genome Institute. N.p., 07 Nov. 2013. Web. 11 May 2015.

[5] "Sulfur Metabolism in Phototrophic Sulfur Bacteria." Sulfur Metabolism in Phototrophic Sulfur Bacteria. N.p., n.d. Web. 11 May 2015.

Figures

[F1]

Alt
Chromatium



Author

Page authored by Sukhwinder Kaur, student of Prof. Katherine Mcmahon at University of Wisconsin - Madison.