Bivalve symbionts. (exam relevant)

This paper is relevant to a commonly occurring exam question regarding symbiosis and I also found it an extremely interesting read. 

Symbionts have been noted and observed in all types of ecosystems, a lot of them marine with the corals and their zooxanthellae to jellyfish and their symbionts as well.  This study looked at marine bivalves, more specifically the species, deep sea mussel- Bathymodiolus- which has for years had an association with chemosynthetic bacteria.  It has been clearly noted that from these studies the bacteria are usually only associated/ restricted to the adults except hosts that linearly transfer them.

These mussels occur commonly and globally at hydrothermal vents and cold seeps and harbor their intracellular symbionts in their gills and these are known as bacteriocytes. The individuals are just like the Euprymna- bobtail squid- these mussels acquire their symbionts from the external environment even if the process is still unknown specifically. TEM studies have demonstrated that juveniles as small as 0.12mm appear to already harbor symbionts.

This study by Wentrup et al (2013) wanted to observe the process and specificity of the infection process and they saw a shift from widespread infection to a specific colonization of the gills in these juvenile mussels, hence the title of the paper being this.

In this study the authors essentially just used FISH to observe the bacteria from beginning to end of the infection process to see whether symbiotic acquirement was specific or whether it was just from a whole body colonisation and then specific development of certain bacteria. They were able to look at both symbionts and the other eubacterial probes, as they used FISH specific signals for these symbionts.

What they saw was that in the juvenile individuals gills at a certain size there were only symbiont specific bacteria and no eubacterial probes present thus indicating that only the specific symbionts can colonize and enter the gills, from further analysis of all host tissues they saw a combination of both regular bacteria and symbionts thus demonstrating that all round colonisation of host tissues does infact then lead to specific symbiont colonisation of the gills. This specific colonisation of just the gills and not any other areas with symbionts on top of eubacteria is most probably due to the fact that their presence does not outweigh their nutritional input. This is what was concluded by the authors.

This paper is very interesting because once again it shows that FISH can be applied to numerous areas and has once again been used to show colonisation (specific) of symbionts within a host. I’m sure after this more studies will be done to see exactly how the developmental process occurs.

Hope you enjoyed this read, the paper is available at:

http://www.nature.com/ismej/journal/vaop/ncurrent/pdf/ismej20135a.pdf

 

 

 

Reference:

Wentrup,C., Wendeberg,A., Huang,J., Borowski, C. & Dubilier. N. (2013). Shift from widespread symbiont infection of host tissues to specific colonization of gills in juvenile deep-sea mussels. International society for Microbial ecology.