Aeromonas Hydrophila

From MicrobeWiki, the student-edited microbiology resource

A Microbial Biorealm page on the genus Aeromonas Hydrophila

Classification

Higher order taxa

Cellular organism; Bacteria; Proteobacteria; Gammaproteobacteria; Aeromonadales; Aeromonadaceae; Aeromonas.

Species

NCBI: Taxonomy

Aeromonas hydrophila

Subspecies: Aeromonas hydrophila subsp. anaerogenes, Aeromonas hydrophila subsp. decolorationis, Aeromonas hydrophila subsp. dhakensis, Aeromonas hydrophila subsp. hydrophila ATCC 7966, and Aeromonas hydrophila subsp. ranaei [19].

Description and significance



Aeromonas hydrophila is the most well known of the six species belonging to the genus Aeromonas. It is rod- shaped, non- spore forming, oxidase- positive, glucose- fermenting, facultative anaerobic, gram- negative bacterium that are inhabitant to aquatic environments [1, 2]. This bacterium can be found in fresh, brackish, estuarine, marine, chlorinated and unchlorinated water supplies worldwide, with highest numbers obtained in the warmer climates [1, 2, 3, 4]. The bacterium has optimal growth at 28°C but can also grow at the limits from 4°C to 37°C [1]. Some strains of Aeromonas hydrophila are capable of causing disease in fish and amphibians as well as in humans who may acquire infections through open wounds or by ingestion of an adequate number of the organisms in water or food. This bacterium can digest materials such as gelatin, hemoglobin, and elastin. Aeromonas hydrophila was isolated from diseased cold- and warm- blooded animals for over 100 years and from humans since the early 1950s [1, 5]. It is also hard to kill because it is a resistant bacterium. Aeromonas hydrophila is resistant to chlorine, refrigeration or cold temperatures [24].



Genome structure

The complete genome of Aeromonas hydrophila strain ATCC 7966T was sequenced [14]. The genome is comprised of a single circular 4,744,448 bp chromosome with 61.5% GC content [20]. Its entire genome consists of 4,122 protein coding genes and 159 RNA genes: 128 tRNA genes amd 30 rRNA genes. It was possible to assign putative functions to 72.3% of the CDSs, while 21.5% possessed similarity to genes of unknown function, and no function could be proposed for 6.2% of the CDSs [21]. The complete genome sequence of Aeromonas hydrophila ATCC 7966T reveals mechanisms contributing to virulence and metabolic condition that allow the organism to grow in a variety of environment and explain how Aeromonas hydrophila is able to survive in polluted or oxygen- poor environments and to colonize and cause illness in humans and other hosts. However, two recognized virulence markers, a type III secretion system and a lateral flagellum, that are reported in other Aeromonas hydrophila strains are not identified in the sequenced isolate, ATCC 7966T. Given the ubiquity and free- living lifestyle of this organism, there is relatively little evidence of fluidity in terms of mobile elements in the genome of this particular strain. Thus, the Aeromonas hydrophila genome sequence provides valuable insights into its ability to flourish in both aquatic and host environments [14].

A number of virulence factors produced by Aeromonas species, however, their association with diarrhea have not been clearly linked [14]. Recently, a cytotoxic enterotoxin (Act), a heat- unstable cytotonic enterotoxin (Alt), and a heat- stable cytotonic enterotoxin (Ast) has been characterized from a diarrheal isolated of Aeromonas hydrophila. The Act is a single- chain polypeptide that is one of the primary genes to make this species pathogenic. Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. Alt and Ast also have genes that contribute to its toxicity, but are not related to cholera toxin [6].

Cell structure and metabolism

Aeromonas hydrophila are gram- negative straight rods with rounded ends. They usually grow from 0.3 to 1.0 μm in diameter and 1.0 to 3.5 μm in length. Aeromonas hydrophila does not form endospores, and can grow in temperatures as low as 4°C. This bacterium is motile by polar flagella. Aeromonas hydrophila are heterotrophic organisms. They can exist in both aerobic and anaerobic environments, and ferment glucose. Aeromonas hydrophila can also digest gelatin, hemoglobin, and elastin [23, 24].

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

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

Current Research

Enter summaries of the most recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Rachel Larsen