Pasteuria ramosa

Pasteuria ramosa
Daphnia magna infected with Pasteuria ramosa
Scientific classification
Kingdom:	Bacteria
Division:	Firmicutes
Class:	Bacilli
Order:	Bacillales
Family:	Pasteuriaceae
Genus:	Pasteuria
Species:	P. ramosa
Binomial name
Pasteuria ramosa

Pasteuria ramosa is a gram-positive, endospore-forming bacterium in the Bacillus/Clostridia clade within Firmicutes. It is an obligate pathogen with cladoceran crustaceans from the Daphnia genus serving as its hosts. An established and widely used coevolutionary model of host-pathogen interactions exists with P. ramosa and D. magna.

P. ramosa is an obligate pathogen and it can only grow inside its host. Transmission between hosts takes place through the endospore stage, and is strictly horizontal. These endospores are highly resistant to different environmental stresses and can remain in the environment for decades without any deleterious effects. The infection starts when a Daphnia has ingested a spore of P. ramosa during filter feeding. The spore activates and attaches to the host esophagus. The pathogen then enters the body cavity of the host by penetrating the esophagus wall. Once inside the body cavity, the bacterium begins to propagate in cauliflower like colonies. After the infection has spread throughout the host, the bacterium begins to sporulate. The spores are shed into the environment from the dead host and can remain in the sediment for decades while maintaining their infectivity.

The infection success of P. ramosa depends on its ability to attach to the host esophagus and to spread into its body cavity where the propagation of the pathogen takes place. The attachment step of the infection depends on the genotypes of the host and the bacterium, meaning that only certain host genotypes can be infected by certain strains of the bacterium. During P. ramosa infection, the size of the Daphnia increases significantly. This phenomenon is known as pathogen-induced gigantism. The fecundity of the host is reduced due to the early induction of castration. In addition, the lifespan of the host is significantly reduced.

P. ramosa has been found in D. magna, D. pulex, D. longispina,D. dentifera, and Moina rectirostris.

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Wikipedia