A HOT AND SOUR SOUP: THE CONTINUUM OF SULFUR MICROBIAL COMMUNITIES FROM THERMAL, NON-THERMAL, AND DOWNRIGHT CHILLY CAVES

Caves that provide sulfur-rich environments for microbial communities come in a variety of temperatures from the decidedly cool to painfully hot. This should come as no shock since other sulfur systems also span a great range of temperatures, but in the case of sulfur caves their serious study is so new that even simple comparisons are still yielding exciting surprises to the small number of investigators focusing on them.

Although the dominance of the sulfur chemistry in these systems may seem as if it swamps other variability like that of temperature, a careful comparison of these systems at a range of temperatures shows that to be a naïve notion. If a temperature indicator could be reliably detected, it could be of great use as a biosignature on Earth and elsewhere. Are there any possibilities that such an indicator might exist? We believe the answer may be “yes” and will discuss our evidence so far.

The difficulty of characterizing all biomineral rich microbial communities demands that we not naively rely on any single or small number of methods but try to piece the whole jigsaw together one tiny fragment at a time. This is particularly critical in solidly nailing down any connections between living representatives and the lithified materials that they create and leave behind for us to find and puzzle over. The temptation to rely on morphology must be resisted as form alone can be highly misleading. We will discuss our results to date comparing metabolism, biodiversity, and mineralization between the temperature regimes of caves in Mexico, Colorado, and elsewhere and address the question, “What is the minimum palette of techniques necessary to adequately characterize a system without jumping to initial unfounded conclusions?”