Pseudoalteromonas atlantica

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A Microbial Biorealm page on the genus Pseudoalteromonas atlantica

Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Alteromonadales; Pseudoalteromonadaceae; Pseudoalteromonas (5)

Species

Pseudoalteromonas atlantica T6c Description and significance Credit: SEM picture by Chandra Carpenter at the University of Georgia (1) Pseudoalteromonas atlantica was first isolated from a marine algae in the coastal marine environment(1). It is a rod-shaped, motile, gram-negative bacteria that is also found in the ocean world wide. The bacteria is motile through the means of a single polar flagellum, which helps it move back and forth between solid surfaces and the open ocean in search of food sources(1). The bacterial cells usually occur singly or in pairs. It obtains energy through chemoorganotrophic mechanisms(1). It is also a biofilm-forming bacteria, which becomes important for bioremediation. It usually is found with marine eukaryotic hosts, such as crabs and seaweed(1). The genome of Pseudoalteromonas atlantica was sequenced due to its production of acidic extracellular polysaccharides during biofilm formation that show potential in element recycling, detoxification, and materials production(1). It is also an agar-decomposing bacteria that produces agarase which is widely used and now, because of P. atlantica, can be commercially made(1). Genome structure The size of P. atlantica's genome is 5.187007 megabases, and its GC content is 45%(1). Its chromosome is circular in shape (1). The bacteria does not have any known plasmids. Cell structure and metabolism Pseudoalteromonas atlantica is psychrotrophic, as well as chemoorganotrophic(6). It is capable of aerobic metabolism for energy, but not fermentation. Some important molecules it produces include acidic extracellular polysaccharide(EPS), enzymes, such as agarase, that hydrolyze agar, alginate, and carrageenan, signaling molecules, such as homoserine lactones, and proteases(1). It produces EPS in large amounts in order to concentrate nutrients and provide substrates within its biofilm for other marine microorganisms. In order to do this, it gains energy for EPS production by colonizing solid surfaces quickly, using its secreted enzymes to process and take up substrates(1). Another interesting ability of this bacteria is that it has the ability to switch adhesin extracellular polysaccharide on and off(1). The on-off switch is essential to this bacteria's life cycle because of its need to migrate from open ocean to solid surface. Adhesins are switched off when the bacteria needs to loose its attachments to a solid surface and travel the ocean(1). Once a favorable surface is found, the bacteria need adhesin for attachment. After attachment, it begins to form biolfilms. Pseudoalteromonas atlantica is incapable of using DL-malate, D-sorbitol, or m-hydroxybenzoate for catabolic metabolism(6). It is capable of gelatin hydrolysis. Gelatin is a protein that contains essential amino acids and comes from the hydrolysis of collagen from natural sources. This bacteria breaks down gelatin polymer into individual amino acids for nutrient. Ecology Pseudoalteromonas atlantica's production of acidic extracellular polysaccharide(EPS) in its biofilm is particularly useful in bioremediation. The biofilm can be important in controlling toxic metal concentrations in marine environments because it can absorb 20-40% of trace metal lead(1). The bacteria has an unusual ability to regulate its EPS production. It has a DNA recombination system that involves reversible insertion of a mobile element, called IS 492(2). The insertion of IS 492 at an EPS site makes variable expressions of EPS possible. This system is responsive to changes in environmental conditions, therefore the bacteria can regulate its production of EPS in terms of the present environmental condition. Tranposon IS492's effect on EPS production is discussed in more detail below in the research section. Pathology Pseudoalteromonas atlantica has been shown to cause shell disease-infected edible crabs. Studies show that the extracellular products or ECP of Pseudoalteromonas atlantica cause rapid death when injected into healthy crabs. The research is outlined in detail in the next section. There are no studies that show that Pseudoalteromonas atlantica is in any way harmful to humans. Current Research One recent research showed that the ECP of P. atlantica lead to fatality in edible crabs, Cancer pagurus. ECP functions by causing rapid decline in the circulating hemocytes(3). The blood cells would begin to clump together. The diseased crabs show symptoms such as limb paralysis, eyestalk retraction, and marked decrease or lack of antennal sensitivity(3). These symptoms suggest an attack of the nervous system. ECP is not inactivated with high heat treatments or proteinase K digestion. The lipopolysaccharide(LPS) of Pseudoalteromonas atlantica was studied as a possible candidate for the main virulence factor. LPS was injected into healthy crabs and shown to cause the same symptoms and eventual death in an average of 90 minutes(3). However, with injection of LPS, no decline of hematocytes was observed. Instead of clumping, the hematocytes degranulated and eventually lysed(3). Results show that LPS from Pseudalteromonas atlantica is the main virulence factor for edible crabs. Another recent research done on Pseudoalteromonas atlantica was by Higgins, Carpenter, and Karls in the Department of Microbiology of the University of Georgia. These researchers found that the precise excision of mobile element(transpon) IS492 on the P. atlantica chromosome regulated the EPS production on-off switch(2). The excision of IS492 turns EPS production from OFF to ON. This discovery is not so surprising due to the fact that in most organisms, DNA rearrangements, such as deletions,insertions, and inversions, control DNA expression. The excision of transposon IS492 is done by enzyme transposase, whose gene is named MooV(2). The frequency of transposase-dependent excision is very high and is regulated by the level of MooV. When MooV level or, in other words, the transposase expression is high, transposase reaches a critical threshold required for excision of transposon IS492. In summary, when a cell senses a signal to produce more EPS, the MooV level increases, which increases external expression of transposon, which then allows excision of IS492 and turns EPS production from OFF to ON, once reaching a critical concentration(2). A final recent research focuses on P. atlantica possible contribution to bioremediation. P. atlantica's effect on aluminum alloy was studied by a research team from the University of Rhode Island. The study comprised of EIS analysis of a control, aluminum alloy medium without P. atlantica, and a sample of aluminum alloy with the bacteria(4). The results of the EIS analysis suggested that the presence of the bacteria lowered the charge transfer resistance for aluminum alloy, which means the corrosion resistance was reduced, and the corrosion rate was increased(4). It was suggested that this result may be attributed to the ability of the bacteria to form a biofilm containing acidic polymers on the surface of the metal alloy. The acid polymers would maintain a corrosive environment on the surface and cause the increase in corrosion rate(4). This hypothesis is supported by the fact that the acidic extracellular polysaccharide is produced in the bacteria's biofilm. References 1. Pseudoalteromonas Atlantica T6c Genome Home Page. http://genome.jgi-psf.org/finished_microbes/pseat/pseat.home.html 2. Brian P. Higgins; Chandra D. Carpenter; Anna C. Karls. 2006. “Chromosomal context directs high-frequency precise excision of IS492 in Pseudoalteromonas atlantica”. Biological Sciences. 2006 February; 104(6): 1901-1906 3. Carolina Costa-Ramos; Andrew F. Rowley. 2004. “Effect of Extracellular Products of Pseudoalteromonas atlantica on the Edible Crab Cancer Pagurus”. Appl Environ Microbiol. 2004 February; 70(2): 729–735. 4. H. Cai, R. Brown; M.A. Rivero-Hudec. 2003. “Effect of Pseudoalteromonas atlantica on the Corrosion of Aluminum Alloy 2024”. 204th Meeting. The Electrochemical Society. http://66.218.69.11/search/cache?ei=UTF-8&p=pseudoalteromonas+atlantica&fr=yfp-t-501&u=www.electrochem.org/dl/ma/204/pdfs/0440.PDF&w=pseudoalteromonas+atlantica&d=VnX0KOrnO2q3&icp=1&.intl=us 5. Pseudoalteromonas Atlantica Genome Page; http://cmr.tigr.org/tigr-scripts/CMR/GenomePage.cgi?org=gaph KMG Summarized by Christina Shayevitz