Dechlorosoma suillum
Andy Jugan

I chose to investigate Dechlorosoma suillum because I feel that microbes are generally viewed in a negative way, however many microbes such as D. suillum can actually be helpful. Additionally, it is fascinating that there are still many bacteria just being discovered. D. suillum is an example of one of these newly discovered bacterium. Finally, D. suillum is a good example of the type of debate that can emerge when a new bacterium is discovered and needs to be classified.

D. suillum was discovered by Coates et al in 1999 in swine waste and was later classified by Achenbach et al. in 2001. De means from, Chloros means green (which implies chlorine), soma means body. So the entire genus essentially means dechlorinating body. Suillum means pertaining to swine (Brenner et al., Vol. 2C, 2001). D. suillum is of the Bacteria Domain, Proteobacteria Phylum, Betaproteobacteria Class, Rhodocyclales Order, Rhodocyclaceae Family, and Dechlorosoma Genus (Brenner et al., Vol. 2A, 2001).

There has been controversy over this taxonomic naming of D. suillum. Some
argue that D. suillum is essentially the same species as Azospira oryzae (Tan and Reinhold-Hurek 2003). A. oryzae was first discovered by Reinhold-Hurek and Hurek in 2000. According to Tan and Reinhold-Hurek, D. suillum and A. oryzae belong to the same species for four reasons. First, their 16s rDNA shows 99.9% similarity. Second, the SDS-Soluble proteins show almost identical patterns in electrophoregrams indicating a genomic similarity. Third, the two bacteria share most of the same phenotypic characteristics like carbon source utilization enzymic activities and diazotrophy noting that the difference of a single characteristic (dissimilatory perchlorate reduction) does not justify separation into two species or genera. Fourth, the DNA-DNA binding of 90-92% is above suggested limits for species identity. According to Bacterial Nomenclature Up-to-date, a webpage designed to keep track of bacterial nomenclature, Dechlorosoma suillum and Azospira oryzae are considered “subjective synonyms”, however in Bergey’s Manual of Systematic Bacteriology are D. suillum and A. oryzae listed as two separate species.

D. suillum is a gram negative, nonsporeforming motile rod that is approximately 0.3 x1.0 µm in size. Cells have a single polar flagellum, occur singly or in chains, and contain c type cytochromes (Achenbach et al., 2001). They are nonfermentative heterotrophic facultative anaerobes which are capable of dissimilatory (does not incorporate reduced products into the cell) reduction of nitrate (NO3), oxygen, chlorate (ClO3-), and perchlorate (ClO4-). It can not reduce 2,6-anthraquinone disulfonate, fumarate, malate, selanate, sulfate, Fe(II), and Mn(IV). D. suillum can grow using acetate, butyrate, ethanol, lactate, propionate, and Casamino acids. It does not use benzoate, catechol, citrate, formate, glucose, glycerol, methanol, or hydrogen as electron donors. Enrichment cultures can be made by suspending and incubating samples in anaerobic liquid medium consisting of acetate as the electron donor and chlorate as the electron acceptor. Optimal conditions for growth include 0% NaCl, pH 6.5, and 37ºC (Brenner et al., Vol. 2C, 2001). Some unique features include the ability to couple growth to the complete oxidation of organic electron donors and the complete reduction of perchlorate and chlorate to chloride (Achenbach et al, 2001).

D. suillum have been found in many diverse environments to include uncontaminated and contaminated field samples, ex situ bioreactors treating perchlorate contamination, in soil and lake samples collected from Antarctica, and in swine waste (Brenner et al., Vol. 2A, 2001).

A major contribution of D. suillum to our society is its role in bioremediation. A good example of the way D. suillum can be utilized was published by Schnoor et al. in their feasibility study of using bioremediation at the Longhorn Army Ammunition Plant (LHAAP) in Marshall, Texas. Perchlorates are used as an oxidant in solid rocket fuel and in explosives. Perchlorate contamination occurred at LHAAP due to assembly and disassembly of missile defense systems associated with the Cold War and post Cold War eras respectively. Perchlorate contamination is of a major concern because Perchlorate salts, such as ammonium perchlorate are highly soluble in water. Perchlorates health risks include promotion of growth of thyroid tumor cells, targets bone marrow, muscle, and possibly cause aplastic anemia (Schnoor et al. 2002).

References

Achenbach, L. A., Michaelidou, U., Bruce, R. A., Fryman, J., and Coates, J. D. 2001. Dechloromonas agitata gen. nov., sp. nov. and Dechlorosoma suillum gen. nov., sp. nov., two novel environmentally dominant (per)chlorate-reducing bacteria and their phylogenetic position. Int J Syst Evol Microbiol 51, 527-533.

Bacterial Nomenclature Up-to-date. Genus Azospira.
http://www.dsmz.de/bactnom/nam6740.htm

Bacterial Nomenclature Up-to-date. Genus Dechlorosoma. http://www.dsmz.de/bactnom/nam7102.htm

Brenner, D. J., Krieg, N. R., and Staley, J. T., Eds. 2001. Bergey’s Manual of Systemic Bacteriology. Second Edition. Volume Two: The Proteobacteria, Part A: Introductory Essays. 156, 193, 198, 211.

Brenner, D. J., Krieg, N. R., and Staley, J. T., Eds. 2001. Bergey’s Manual of Systemic Bacteriology. Second Edition. Volume Two: The Proteobacteria, Part C: The Alpha-, Beta-, Delta-, and Epsilonproteobacteria. 887, 903-904.

Reinhold-Hurek, B., and Hurek, T. 2000. Reassessment of the taxonomic structure of the diazotrophic genus Azoarcus sensu lato and description of three new genera and new species, Azovibrio restrictus gen. nov., sp. nov., Azospira oryzae gen. nov., sp. nov. and Azonexus fungiphilus gen. nov., sp. nov. Int J Syst Evol Microbiol 50, 649-659.

Schnoor, J. L., Parkin, G. F., Just, C. L., van Aken, B., Shrout, J. D. 2002. Phytoremediation and Bioremediation of Perchlorate at the Longhorn Army Ammunition Plant Final Report The University of Iowa Department of Civil and Environmental Engineering.

Tan, Z. and Reinhold-Hurek, B. 2003. Dechlorosoma suillum Achenback et al. 2001 is a later subjective synonym of Azospira oryzae Reinhold-Hurek and Hurek 2000. Int J Syst Evol Microbiol 53, 1139-1142.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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