UC San Diego

Only in the last 30 years of science have we discovered that not all life on Earth is based upon photosynthesis. The deep biosphere has emerged as an incredibly diverse ecosystem with life thriving in environmental conditions ranging from sub-zero to 120°C+ temperatures, hyper saline brine pools to low pH environments. This body of work contributes to several key questions about life in the deep biosphere: 1) Which microbes are present in the deep biosphere, 2) what are their sources of energy, 3) how do they attain required nutrients for metabolic function and growth and 4) what is the effect of substrate composition on each of the above questions. In order to address these first order questions, we focused our efforts on Loihi Seamount, off the SE coast of the Big Island of Hawai'i, which provides us with raw materials and microbes for laboratory experiments as well as an in- situ deep-sea laboratory so that we can study effects of microbiology on basalt weathering. Due to the high iron content (̃10-12%), basalts are an attractive source of reduced iron as an energy source for chemolithoautotrophic growth. We explored microbial diversity associated with basaltic glass substrates across a range of different environments in and around Loihi using t-RFLP, clone library data, and culturing/isolation techniques. Results show that [gamma]- and [alpha]-Proteobacteria tend to dominate these surfaces and one of our Fe(II)-oxidizing isolates, a Pseudomonas sp. LOB-7, is represented as one of the most dominant members of the microbial communities on several basalts indicating that perhaps Fe(II)- oxidizing microbes are important players in the microbially mediated dissolution and alteration of basaltic glass. Investigations into substrate specificity by microbes under energy- and nutrient-limiting conditions reveal that Pseudomonas and Shewanella isolates are able to obtain Fe and/or phosphorus directly from a basaltic glass silicate matrix. This finding provides a direct relationship between substrate composition and the activity of particular microbes, which will allow us to provide insights into how substrate composition can control microbial diversity and consequently chemical fluxes between seawater and the basaltic ocean crust