White Paper Title: 
Allying microbial phylogenetic and functional diversity to the geochemical milieu: studying endolithic microbial communities via in situ laboratories

Peter Girguis1*, Geoff Wheat2, Deb Kelley3

1 Harvard University, Cambridge, MA
2 University of Alaska, Fairbanks, AL
3 University of Washington, Seattle, WA
* Corresponding author:


Hydrothermal vents are extremely dynamic, and the mixing of vent endmember effluent and seawater can be quite turbulent.  Interestingly, we have observed that -within the porous sulfide walls of a chimney -stable temperature and fluid chemistry gradients may be established. Previous efforts (Schrenk et al, 2003) have shown that microbes living within these sulfides exhibit a zonation that may relate to these gradients, though the temporal and spatial nature of the observed zonation is poorly constrained.  Furthermore, the successional nature of endolithic microbial communities - and the degree to which this is influenced by the dynamics of physico-chemical conditions - is largely unknown.

To investigate the microbial ecology of these structures at the Endeavour segment of the Juan de Fuca Ridge system, Deb Kelley and we developed and deployed a series of in situ endolithic incubators, consisting of titanium sleeves packed with sterile substrates equipped with temperature probes and small-volume water samplers.  Samplers were deployed within the sulfides for periods ranging from one week to over a year.  Patterns in phylogenetic and functional diversity suggest that specific archaeal and bacterial groups are early colonizers of hydrothermal sulfides. Via quantitative-PCR and FISH, we also observed temporal and spatial changes in the abundance of dominant endolithic phylotypes, which provide insight into the phylogenetic and functional “succession” within hydrothermal sulfides.  Our ongoing geochemical and metagenomic analyses aims to examine which geochemical features -if any- are related to the observed microbial community dynamics and physiologies.  

Contributions to Integration and Synthesis

While significant advances in vent microbiology have been made in recent years, there is a paucity of information on the endolithic microbial communities.  These communities may have a pronounced influence on vent geochemical composition, and they likely play a significant role in carbon and nitrogen cycling within the vent community.  We suggest that these relationships cannot be discerned or constrained without a concerted, multidisciplinary effort to relate the patterns in geochemistry, mineralogy and microbiology.  To that end, we have used this project as a model for coordinating efforts and analyses, as well as integrating data with varying degrees of temporal and spatial resolution.  We hope to discuss our results to date, as well as the logistical and organizational approaches that were most (and least) effective in this program.  It is our overarching goal to work with the larger community in developing more sophisticated approaches to integrating and synthesizing disparate biological and geochemical datasets.