Rahnella aquatilis

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A Microbial Biorealm page on the genus Rahnella aquatilis


Higher order taxa

Domain (Bacteria); Phylum (Proteobacteria); Class (Gammaproteobacteria); Order (Enterobacteriales); Family (Enterobacteriaceae); Genus (Rahnella)


Species (aquatilis)

Rahnella aquatilis

Description and significance

Rahnella aquatilis is a relatively rare gram-negative rod-shaped bacteria which has been found in fresh water, soil, certain animals, such as snails [5] and certain beetles [4], and isolated human clinical specimens[2]. This bacterium is of importance because of its abundance and its disease-causing ability in humans. Many different strains have been isolated, and presumably more will be disocvered.

Genome structure

As of the year 2000, at least 70 strains of Rahnella aquatilis have been identified [1]. According to the National Center for Biotechnology Information (NCBI), the whole genome has been sequenced for Rahnella aquatilis strain Y9602. This particular strain has a genome consisting of 4,864,217 base pairs, with two identified plasmids [2]. Another strain, Rahnella aquatilis CUETM 77-115, was shown to have a genome consisting of 5,440,269 base pairs and a G-C content of 52.1% [3].

Cell and colony structure

Rahnella aquatilis is gram-negative rod-shaped bacterium, about 2-3 microns in length. Strain ISL 19 was isolated from soybean rhizosphere, and was seen to have several flagella for motility [6]. The bacterium can be readily cultured in the laboratory.


Rahnella aquatilis is a facultative anaerobe (it can live in the absence or presence of oxygen) that fixes Nitrogen [2]. Rahnella aquatilis metabolizing whey lactose produces high levels of organic acids (except for lactic acid) [7].


Rahnella aquatilis is named so because of its prevalence in fresh water. It has been found around the globe in places like the United States, Korea, Japan, Russia, the Ukraine, and Egypt. Rahnella aquatilis has also been found in humans, soil, and snails [5]. One of the most unusual places for the the microbe to have been found was inside the gut of certain speicies of longicorn beetles in Korea [4].


Rahnella aquatilis is pathogenic in humans. The organism can be diagnosed in patients via blood cultures, respiratory washings, and in wound cultures. Various infections, such as bacteremia (from renal infection), sepsis, respiratory infection, and urinary tract infection can be the result. One case involved an 11-month-old girl with congenital heart disease who developed infective endocarditis [8]. Another case involved a 76-year-old male who had prostatic hyperplasia presenting with acute pyelonephritis [9]. It is noted that Rahnella aquatilis can potentially cause life-threatening infections in humans, infants and adults alike, especially the immunocompromised and organ transplant recipients. Treatments have included intravenous and oral levofloxacin therapy (and other members of the quinolone family).


[1] J Chemother. 2000 Feb;12(1):30-9. <http://www.ncbi.nlm.nih.gov/pubmed/10768513>

[2] R.J. Martinez. J Bacteriol. 2012 Apr;194(8):2113-4. <http://www.ncbi.nlm.nih.gov/genome/?term=Rahnella%20aquatilis>

[3] Robert Martinez, University of Alabama. <http://genome.jgi-psf.org/rahac/rahac.info.html>

[4] Park, Doo-Sang, Hyun-Woo Oh, Won-Jin Jeong, et al. "A Culture-Based Study of the Bacterial Communities within the Guts of Nine Longicorn Beetle Species and their Exo-enzyme Producing Properties for Degrading Xylan and Pectin." The Journal of Microbiology, October 2007, p. 394-401.

[5] Brenner, Don J., Hans E. Muller, Arnold G. Steigerwalt, et al. "Two new Rahnella genomospecies that cannot be phenotypically differentiated from Rahnella aquatilis." lnternstional Journal of Systematic Bacteriology (1 998), 48, 141 -149.

[6] Kim, Kil Yong, Diann Jordan, and Hari B. Krishnan. "Rahnella aquatilis, a bacterium isolated from soybean rhizosphere, can solubilize hydroxyapatite." FEMS Microbiology Letters Volume 153, Issue 2, 15 August 1997, Pages 273–277.

[7] Pintado, Manuela E., Ana I.E. Pintado, and F. Xavier Malcata. "Fate of Nitrogen During Metabolism of Whey Lactose by Rahnella aquatilis." Journal of Dairy Science, Volume 82, Issue 11, November 1999, Pages 2315-2326.

[8] Matsukura H., Katayama K., Kitano N., et al. "Infective endocarditis caused by an unusual gram-negative rod, Rahnella aquatilis." Pediatric Cardiology, 1996 Mar-Apr; 17(2): 108-11.

[9] Tash, Kaley. "Rahnella aquatilis Bacteremia from a Suspected Urinary Source." Journal of Clinical Microbiology. May 2005, vol. 43 no. 5, 2526-2528.

Edited by Christopher John Connor, student of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences, http://www.usm.maine.edu/bio