Shewanella denitrificans

A Microbial Biorealm page on the genus Shewanella denitrificans

Classification

Higher order taxa

Bacteria, Proteobacteria, Gammaproteobacteria, Alteromonadales, Shewanellaceae

Species

NCBI: Taxonomy

Shewanella denitrificans

Description and significance

The Shewanella genus is a diverse group of marine gamma-proteobacteria, ranging from psychrophilic, to piezophilic, to psychrotolerant, to mesophillic [1]. Some species are noted for their pathogenicity, still others are studied for their diversity of electron transport systems. They are capable of anaerobic respiration using a large spectrum of electron acceptors in addition to aerobic respiration. Shewanella denitrificans is noted primarily for its ability to vigorously denitrify nitrate and nitrite, converting these molecules to gaseous nitrogen. Although there are many other members of the genus that are denitrifiers, S. denitrificans is unique in its enthusiastic denitrification. It was first described in 2002 by Brettar et. al. [2], who aligned it with the genus and distinguished it as a novel species based on physiological and 16S rRNA comparisons, among others. Like the other organisms in its genus, S. denitrificans is a rod shaped, gram-negative bacterium with polar flagella. It is found at the oxic-anoxic interface and was first isolated from the Gotland Deep, a basin in the Baltic Sea. It was first isolated as three strains, called OS217T, S220 and OS226, which were phylogenetically identified as a single species. S. denitrificans is a mesophilic organism with an optimum growth temperature of 20-25 C. Based on its fatty acid composition and genome sequence, S. denitrificans is most related to S. baltica, S. putrefaciens and S. frigidimarina within the Shewanella genus, but has a different growth optimum from these species. In addition, its enzymatic activities, electron acceptors, and utilization of substrates distinguish it from the others in its genus.

Genome structure

The genome for Shewanella denitrificans was completed on April 11, 2006 by the DOE Joint Genome Institute/Pacific Northwest National Laboratory. It is a circular genome that is 454906 bases long and code for 3905 genes. The genome has a GC content of 45% and can be found in more detail at NCBI

Cell structure and metabolism

The marine bacteria Shewanella denitrificans is rod shaped and approximately 0.5-0.8 micrometers wide by 2-3 micrometers long. It is Gram-negative and has flagella located at its poles [3].

Although this species is facultatively anaerobic, its denitrification capabilities are what make it important in the marine environment. Denitrification is an important part of the nitrogen cycle; it is the counterpart to nitrogen fixation [4]. Denitrification is found in a wide variety of bacteria as well as a few Archaea and fungi. It is a complicated process and requires a suite of proteins for it to occur.Shewanella denitrificans' can reduce nitrate or nitrate and use them as terminal electron acceptors, in the process converting the nitrogen oxides to nitrogen gas. For S. denitrificans The process of denitrification occurs in the periplasm.

Anaerobic respiration – denitrification; reduce nitrate or nitrite to nitrogen; unfixing, part of N cycle, occurs in anoxic environments, also possible to go directly to ammonia – anammox, need nrf-gene

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=232623&blobtype=pdf

Ecology

S. denitrificans is found at the oxic-anoxic interface in the marine environment. It is an important species in this region because most of the denitrification that occurs happens at this interface, and S. denitrificans contributes significantly to the total denitrification of the system [5].

Pathology

Shewanella putrifaciens - infection in fish passed to humans Shewanella septicemia - caused lethal sepsis in human

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Proposed to make two sub-genera based on psychrotolerance and piezophily.

References

Brettar, I.; Christen, R.; Hofle, M.G. Shewanella denitrificans sp. nov., a vigorously denitrifying bacterium isolated from the oxic--anoxic interface of the Gotland Deep in the central Baltic Sea. International Journal of Systematic and Evolutionary Microbiology [Int. J. Syst. Evol. Microbiol.]; vol. 52, no. 6, pp. 2211-2217; 2002 ISSN: 1466-5026 [6]

Kato, Chiaki; Nogi, Yuichi. Correlation between phylogenetic structure and function: examples from deep-sea Shewanella. F E M S Microbiology Ecology, VOL. 35, NO. 3, pp. 223-230; 2001 ISSN: 0168-6496 [7]

Otsuka, Taiga; Noda, Takahiro; Noguchi, Akinori; Nakamura, Haruki; Ibaraki, Kazuo; Yamaoka, Kotaro. Shewanella infection in decompensated liver disease: a septic case. Journal of Gastroenterology. VOL. 42, NO. 1, pp. 87-90; 2007

Zumft, W.G. (1997): Cell biology and molecular basis of denitrification. In: Microbiol. Mol. Biol. Rev. Bd. 61, Nr. 4, S. 533-616. PMID 9409151 [8]

Edited by Karen Rossmassler, student of Rachel Larsen and Kit Pogliano