A Microbial Biorealm page on the genus Shewanella loihica
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Alteromonadales; Shewanellaceae; Shewanella; Shewanella loihica
Description and significance
The PV-4T marine bacterial strain of Shewanella loihica was isolated at the deep-sea, hydrothermal Naha Vent from iron-rich microbial mats on the South Rift of Loihi Seamount, Hawaii, in the Pacific Ocean. The bacteria was noted as orange and rodlike with a mean length of 1.8 µm and mean width of 0.7 µm. Growth on Luria–Bertani agar plates showed S. loihica to be psychrotolerant at temperatures between 0-42 degrees C (Haichun Gao et al.). The ability of Shewanella to survive at such extremes in temperature in conjunction with their notable respiratory diversity make these bacterial species supreme interests of study. Shewanella have been investigated in the past to understand how their physiology contributes to their varied roles in the environment and have allowed for applicable uses in biotechnology (Gralnick JA et al.). Shewanella are also potentially pathogenic with respect to rare cases of gastrointestinal infection in recent reports in both Israeli & Japanese hospitals (Otsuka T et al.).
The S. loihica genome is recorded as having 4,602,594 nucleotides, 3,859 protein genes, and 124 RNA genes (Kegg Encyclopedia). PV-4(T) exhibited 16S rRNA gene sequence similarity levels of 99.6% to Shewanella aquimarina, 97.5 % to S. marisflavi, 50.5 % to S. aquimarina and 8.5 % to S. marisflavi (JGI Microbes). The GC content of Shewanella loihica PV-4, as taken from the NCBI database, is 53.7%.
Cell structure and metabolism
The S. loihica is noted as being Gram-negative (having both outer and inner membranes) and motile through polar flagella (Haichun Gao et al.). Metabolizing through facultative means, S. loihica has been studied extensively for its electron transport systems and ability to use a variety of electron acceptors under anaerobic conditions. Such compounds include iron, manganese, uranium, nitrate, nitrite and fumurate, to name a few (JGI Microbes). Studies with Shewanella putrefaciens imply the use of quinone-derivatives as electron shuttles to ferric oxides (Newman et al.) and the notable presence of Q-7 and Q-8 ubiquinones as well as MK-7 menaquinone in the PV-4 strain of S. loihica offer future analysis of this reduction mechanism (Haichun Gao et al.).
Shewanella are are facultative anaerobes, able to grow with or without the presence of oxygen in the surrounding environment. The species is distributed worldwide with a knack for surviving at extremely low temperatures. S. loihica was found to grow at temperatures between 0 to 42°C and pH 4.5–10.0 with optimal growth found at temperatures of 18 °C and pH range of 6.0 – 8.0 (Haichun Gao et al.). The PV-4 strain was an environmental isolate from the Naha Vents, Hawaii, in the Pacific Ocean.
There has yet to be a recorded case of S. loihica having pathogenic capabilities. However, strains of Shewanella have been found to be the cause of gastrointestinal related afflictions. Shewanella septicemia was implicated in the death of a 67 year old Japanese man as a result of a lethal sepsis in conjunction with liver failure (Otsuka T et al.). Another case details Shewanella infections following gastric lavage of a patient with gastrointestinal bleeding (Saidel-Odes et al.).
Application to Biotechnology
Shewanella's flexible use of such a varied number of electron acceptors allows for applications of the bacteria in bioremediation of contaminated metals and radioactive wastes (JGI Microbes), as well as chlorinated compounds and other environmental pollutants. Biotechnological applications of the species extend also to energy-generating biocatalysis (Gralnick JA et al.).
Based on phylogenetic and phenotypic characteristics, bacterium PV-4 was classified in the genus Shewanella within a distinct novel species. The name Shewanella loihica sp. nov. is proposed (Haichun Gao et al.).
Gralnick JA, Hau HH. "Ecology and Biotechnology of the Genus Shewanella." Annual Review of Microbiology. Expected release Volume 60 (2007) June 1 2007 .
Haichun Gao; Obraztova, Anna; Stewart, Nathan; Popa, Radu; Fredrickson, James K.; James M. Tiedje, Kenneth H. Nealson and Jizhong Zhou. "Shewanella loihica sp. nov., isolated from iron-rich microbial mats in the Pacific Ocean." International Union of Microbiological Societies. 2006. 1 May 2007. .
Newman, Dianne K and Roberto Kolter. "A role for excreted quinones in extracellular electron transfer". Nature 405 4 June 2007 .
Otsuka T, Noda T, Noguchi A, Nakamura H, Ibaraki K, Yamaoka K. "Shewanella infection in decompensated liver disease: a septic case." Journal of Gastroenterology. Volume 42 (January 2007) June 1 2007 .
Saidel-Odes, Lisa; Borer, Abraham; Riesenberg; Schlaeffer, Francisc. "Shewanella spp. infection following treatment for upper gastrointestinal bleeding." Scandinavian Journal of Infectious Diseases. Volume 39 (2007) 4 June 2007 .
Kegg Encyclopedia. 1 May 2007 .
Shewanella loihica PV-4. JGI Microbes. (2005) 1 May 2007 .
Shewanella loihica PV-4. US DOE Joint Genome Institute. 4 June 2007 .
Edited by Niru Sivakumar, a student of Rachel Larsen and Kit Pogliano