Coral reefs are threatened throughout the world. A major factor contributing to their decline is outbreaks and propagation of coral diseases. White Plague Disease (WPD) is one of the first described coral diseases. Records show that WPD was responsible for several virulent outbreaks, and it is held responsible for major reef declines worldwide, especially in the Caribbean. Aurantimonas coralicidaas is the WPD-causing pathogen in corals from the Caribbean. Similarly, Thalassomonas loyana has been proposed to be the causative agent of White Plague-like disease in the Red Sea.
One of the most recognized features of tropical, shallow-water corals is their symbiosis with photosynthetic unicellular algae (zooxanthellae) that provide photosynthetically fixed carbon to satisfy their host’s respiratory requirements and facilitate calcification. Corals also live in association with numerous other microorganisms such as bacteria, archaea, protists, endolithic algae, fungi and viruses, the significance of which is only partially.The sum of all organisms is referred to as the coral holobiont.
It is now being recognized that bacteria contribute significantly to the biology of higher-order organisms, and accordingly, bacteria associated with corals are considered a vital component of the coral holobiont. Their potential roles include nitrogen fixation, decomposition of organic materials, production of antibiotic compounds and occupation of space to prevent colonization by pathogens. Coral-associated bacteria have been shown to be host species-specific, diverse and complex, and this assemblage comprises a unique signature that differs from bacterial communities in the surrounding water column.
The collection of organisms associated with and including the host coral animal has been called the coral holobiont. Other words, it is a complex symbiosis between the coral animal, endobiotic alga and an array of microorganisms.
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