[tdwyatt]

I would like to draw your attention to a recent paper on the molecular
mechanisms of coral bleaching under thermal stress.

Vidal-Dupiol J., Adjeroud M., Roger E., Foure L., Duval D., Mone Y.,
Ferrier-Pages C., Tambutte E., Tambutte S., Zoccola D., Allemand D. & Mitta G. (2009) Coral bleaching under thermal stress: putative involvement of host/symbiont recognition mechanisms. BMC Physiology, 9, 14

An online access is available using the following link
http://www.biomedcentral.com/1472-6793/9/14

Spanks and I once had a discussion on whether or not during bleaching events, that zooxanthellae were ejected by the host or they (zoox.) left of their own volition because host conditions were not suitable (this follow whether or not you follow endosymbiosis as an infection or paracytosis by algae originally that was tolerated by the host, or you think of it as a failed attempt at phagocytosis by the host to eat the algae).

 

[Reeftanker3295]

That title totally just gave me a headache. :lol:

 

[aquawolf]

Very interesting article. I am also interested in the results of all of their studies and find this paragraph very helpful.

At the molecular level, the first step of temperature or light induced coral bleaching is the photoinhibition mechanism experienced by the zooxanthellae [13-15]. This often results in the overproduction of reactive oxygen species (ROS) by transport chain electrons [16]. ROS are highly cytotoxic and some of them can easily cross biological membranes leading to severe oxidative stress in both host and symbiotic cells. This oxidative stress can result in the activation of cell necrosis and apoptosis [17,18], which represent two of the six identified ways of endosymbiotic loss during bleaching [18-23]. The four other ways of symbiont disappearance are: i) in situ digestion of zooxanthellae by the coral host [24,25], ii) expulsion by exocytosis or iii) by pinching off [24,26], and iv) host cell detachment [22].

I still need to do further reading to figure out what the "pinching off" actually means.

 

[tdwyatt]

Very interesting article. I am also interested in the results of all of their studies and find this paragraph very helpful.



I still need to do further reading to figure out what the "pinching off" actually means.

Just what it sounds like, a section of the host tissue is sloughed off. Now as to whether or not the host concentrated zooxanthellae in this appendage just prior to sloughing remains to be seen. Some coral spp asexually reproduce by this method (usually fleshy singular polyped species like Cynarina, often seen as "tears" of the body falling from the skeletonized part of the coenenchyme to the substrate, where new skeletons form with time.

 

[Dragonist]

When I read the title I thought symbiotes? Is that was got onto Peter Parker resulting him to become Venom?(super nerd moment yet still cool)

 

[tdwyatt]

Just curious, which do you folks believe is in control of the zooxanthellae that causes the bleaching to occur as the water gets too hot/too much light? Do the zoox leave, or does the coral animal boot them out?

 

[jenglish]

Just curious, which do you folks believe is in control of the zooxanthellae that causes the bleaching to occur as the water gets too hot/too much light? Do the zoox leave, or does the coral animal boot them out?

I always thought of it as expulsion... but I had not in truth really considered the other option. I had thought of zoox as having lost mobility.

 

[tdwyatt]

Very interesting article. I am also interested in the results of all of their studies and find this paragraph very helpful.

At the molecular level, the first step of temperature or light induced coral bleaching is the photoinhibition mechanism experienced by the zooxanthellae [13-15[/URL]]. This often results in the overproduction of reactive oxygen species (ROS) by transport chain electrons [16[/URL]]. ROS are highly cytotoxic and some of them can easily cross biological membranes leading to severe oxidative stress in both host and symbiotic cells. This oxidative stress can result in the activation of cell necrosis and apoptosis [17,18[/URL]], which represent two of the six identified ways of endosymbiotic loss during bleaching [18-23[/URL]]. The four other ways of symbiont disappearance are: i) in situ digestion of zooxanthellae by the coral host [24,25[/URL]], ii) expulsion by exocytosis or iii) by pinching off [24,26[/URL]], and iv) host cell detachment [22[/URL]]
<TABLE border=0 cellSpacing=0 cellPadding=6 width="100%"><TBODY><TR><TD style="BORDER-BOTTOM: 1px inset; BORDER-LEFT: 1px inset; BORDER-TOP: 1px inset; BORDER-RIGHT: 1px inset" class=alt2>At the molecular level, the first step of temperature or light induced coral bleaching is the photoinhibition mechanism experienced by the zooxanthellae [13-15]. This often results in the overproduction of reactive oxygen species (ROS) by transport chain electrons [16]. ROS are highly cytotoxic and some of them can easily cross biological membranes leading to severe oxidative stress in both host and symbiotic cells. This oxidative stress can result in the activation of cell necrosis and apoptosis [17,18], which represent two of the six identified ways of endosymbiotic loss during bleaching [18-23]. The four other ways of symbiont disappearance are: i) in situ digestion of zooxanthellae by the coral host [24,25], ii) expulsion by exocytosis or iii) by pinching off [24,26], and iv) host cell detachment [22]. </TD></TR></TBODY></TABLE>
<!-- END TEMPLATE: bbcode_quote -->

Under thermal stress zooxanthellae photosynthesis leads to intense oxidative stress in the two partners. This endogenous stress can lead to the perception of the symbiont as a toxic partner for the host. Consequently, we propose that the bleaching process is due in part to a decrease in zooxanthellae acquisition and/or sequestration. In addition to a new hypothesis in coral bleaching mechanisms, this study provides promising biomarkers for monitoring coral health.

This mens that the host recognizes the zooxanthellae temporarily as "not-self," a criteria that must be met for the coral animal to allow the dinoflagellate to immunologically allow the zoox. to reman as symbiotic "guests" and not be either digested or ejected. By this definition, ejection then occurs as an immune reseponse, and regardless as to whether or not it is beneficial to the coral animal (ie. that if the zooxanthellae are ejected as an animal response, the animal loses it's free meal ticket), it does so because the superoxidase now makes the coral think it is now under attack by a foreign object/organism. This then might lead us to wonder how the zoox. suppress such recognition under normal circumstances?

Might this mean that hosting zooxanthellae is actually an infection of dinoflagellates?