Hydrothermal vents provide Yeti (crabs) with food

Hydrothermal vents are known to be highly productive ecosystems with primary production occurring through chemoautotrophic microbial production. Hydrothermal vents host a range of metazoan communities, which usually have epi and endosymbiont relationships with these microbes. These microbes include chemolithoautrophic bacteria, which can fix carbon in through various pathways, depending on their phylogenetic group. For example, autotrophic Epsilonproteobacteria fix carbon via the reductive tricarboxylic acid (rTCA) cycle whereas autotrophic Gammaproteobacteria do this via the Calvin-Benson-Bassham cycle (CBB). These differences in carbon fixation pathways are measured through the stable carbon isotope fixtures (δ¹³C) of the microbial primary producers. Many physical and chemical properties near the vents can cause differences in these symbiont communities and differences in trophic ecology of the host.

This study by Zwirglmaier et al. investigates the interactions between a new species of Yeti crab (Kiwaidae sp.) and their microbial episymbionts along the Scotia ridge hydrothermal vents. Using 454 pyrosequencing, sangar sequencing and stable isotope analysis coupled with environmental variables that were measured at the two sampling sites, the study aimed to investigate epibiont diversity and community structure which could then be examined and compared to other decapods occupying similar niches. 

Results showed that the sites were different in chemical and physical properties, with site E2 being 353̈°C and E9 being 383°C. Both sites also had different chemical properties. Majority of the Epsilonproteobacteria found were from the genus Sulfurovum, and majority of the Gammaproteobacteria found were from Leucothrix. There was a clear difference in dominating bacteria, with Epsilonproteobacteria being found mainly on E9 and Gammaproteobacteria being found on E2. The study found also that both sites had different stable carbon isotopic fixtures which meant the sites had different food sources (bacteria). The different levels of stable isotopic fixtures stand for different carbon fixation pathways taking place, which match that of Epsilonproteobacteria or Gammaproteobacteria respectively. 

This study shows the importance at looking at regional differences in microbial community structure on hydrothermal vents, as they provide a unique environment for bacteria to thrive in. The use of sequencing techniques and stable carbon isotope analysis proves that the combination of advanced methods can lead to more in-depth views of metabolic pathways. Further study could be done on the metagenome and chemical properties of the vent to provide insights into the relationship between host (Yeti Crab) and epibiont, involving the pathways. Genetic techniques (e.g. qPCR) could also provide information of the level of gene expression coding for metabolic pathways, and compared between different sites.  

Reference:

Zwirglmaier, K., Reid, W., Heywood, J., Sweeting, C., Wigham, B., Polunin, N., Hawkes, J., Connelly, D., Pearce, D. and Linse, K. (2014). Linking regional variation of epibiotic bacterial diversity and trophic ecology in a new species of Kiwaidae (Decapoda, Anomura) from East Scotia Ridge (Antarctica) hydrothermal vents. MicrobiologyOpen, 4(1), pp.136-150.

http://onlinelibrary.wiley.com/doi/10.1002/mbo3.227/epdf