First come, first provide: On microbial biofilms and metazoan colonisation at deep-sea hydrothermal vents

At deep-sea hydrothermal vents, temperature and chemical gradients lead to the formation of complex ecosystems. Previous studies have shown that newly-formed diffuse-flow hydrothermal vents are first colonised by chemoautotrophic microbes, which form biofilms. Subsequently metazoan larvae settle in the habitat. The larvae respond to the composition, texture and the chemicals produced by the biofilm. The biofilm might even induce the metamorphosis to the sessile adult stage. Thus, chemoautotrophic biofilms may indicate habitat suitability for metazoans as well as provide them fixed carbon. 

In their paper, O’Brien et al. (2015) combined the study of early microbial colonists, fluid chemistry and metazoan colonisation. A volcanic seafloor eruption in the East Pacific Rise in late 2005/early 2006 destroyed the pre-existing habitats and created more than 20 diffuse-flow vents. The studied area was divided into active eruption sites (in-flow) and no apparent eruption sites (no-flow). Temporal Autonomous Multi-Disciplinary Substrates (TAMS) were installed at each site, to serve as experimental colonisation substrates. The samples were collected in two cruises, in 2006 and 2007. Clonal libraries of the chemoautotrophs were assembled using extracted DNA and processing with PCR and DGGE. Voltametry and Microscopy were used to study in-situ fluid chemistry and metazoan colonists respectively

At in-flow sites the measured sulfide concentrations and temperatures were higher than at the no-flow sites. The average oxygen levels were higher at no-flow sites. In general, temperature was correlated with sulfide concentration and both were inversely correlated with oxygen levels.

The TAMS at in-flow sites were dominated by ε-Proteobacteria (on average 90,6%), while the biofilms on no-flow TAMS showed mostly γ-Proteobacteria (on average 84,7%). Unidentified bacterial sequences, α- and δ-Proteobacteria were also detected but only at low levels. The dominance of ε-Proteobacteria could be explained by their adaption to sulfidic habitats, allowing them to be omnipresent in marine geothermal environments. As they use reduced chemical compounds as energy resources, they are dependent on active hydrothermal vents. O’Brien et al. conclude that the chemical and thermal characteristics of the vent seem to control the composition of the biofilm communities. However, they also acknowledge that the experimental assembly has its limitations. 

The analysis of the megafauna at the TAMS showed that siboglinid tubeworms occurred only at in-flow sites. Most of the observed tubeworms were of the species Tevnia jerichonana. The authors assume that the early colonisation of T. jerichonana indicates an adaption to microaerobic conditions and a higher resistance to sulfide than other siboglinidae.

In conclusion the authors state that while they present a first study of the correlation between fluid chemistry, microbial diversity and metazoan colonisation, our knowledge about the role of biofilms in larval settlement is still limited. 

Since its publication in November 2015 the paper doesn’t seem to have gained much online impact and the results themselves don’t appear particularly surprising. However, the authors provide a template of methodology for the study of biofilms at hydrothermal vents. Thus, it would be interesting to see if future papers reported similar findings in other areas of the world. 

Reviewed Paper:

O’Brien, C. E., Giovannelli, D., Govenar, B., Luther, G. W., Lutz, R. A., Shank, T. M., & Vetriani, C. (2015). Microbial biofilms associated with fluid chemistry and megafaunal colonization at post-eruptive deep-sea hydrothermal vents. Deep Sea Research Part II: Topical Studies in Oceanography, 121, 31-40. Link: http://www.sciencedirect.com/science/article/pii/S0967064515002805