White Paper Title: 
Microbe-mineral associations within hydrothermal vent sulfides

Heather Olins (Harvard University, Cambridge, MA)

Variation in microbial communities and metabolic activities among hydrothermal vent sulfides is unconstrained.  There are numerous environmental factors that likely influence the endolithic community, including geochemical and thermal gradients, geochemical flux (e.g. fluid flow), subsurface processes, and chimney age.   In such complex systems, it can be difficult to understand the relationship between chemical, thermal, and biological processes.  Thus, we also have a limited ability to understand (and predict) microbial biogeography within or among chimneys or between vent fields.  Examining microbial ecology in the context of mineralogy may provide a more complete understanding of the diversity, metabolic activity, and overall ecology of these communities.  In addition to understanding hydrothermal systems more completely, linking mineralogy and microbiology in predictive ways could aid in modeling biogeochemical cycles in these systems and perhaps lead to a better understanding of global cycles.

In other more accessible systems, the connections between minerals and microbes have been interrogated, and links have been drawn between specific minerals and the microbial communities associated with them (for example Reardon et al., 2004; Ransom et al., 1999).  The idea of microbe-mineral associations has also been investigated at hydrothermal vents (Kormas et al., 2006), but the focus has been on comparing the communities from inner, middle, and outer sections of chimney walls, rather than looking primarily at specific minerals as drivers of community composition.  At vents, certain mineral precipitates are very common, but their relative abundances vary widely, while others are more rare.  If mineral assemblage itself can be shown to be predictive of microbial community, and in turn activity, a vast number and diversity of archived samples can be investigated, and conclusions can be drawn from them about the community they host and the activity of that community.

Hydrothemal vent chimneys are an ideal locale for studying the relationship between mineral assemblages and microbial communities.  The vent fields along the Juan de Fuca Ridge host markedly different mineralogies.  Most striking, perhaps, is the contrast between Middle Valley and other vent fields.  Middle valley sulfides collected in July 2010 consisted of friable, thin-walled, anhydrite-rich chimneys.  In comparison, sulfides recovered from Main Endeavour, High Rise, and Mothra vent fields lacked obvious anhydrite deposits, were more silicified, and often consisted of thicker walls, friable interiors, and notable pyrite and marcasite deposits.  My research is broadly aimed at better understanding the relationship between mineralogy and microbial community composition and activity, within and among sulfides.