| Abstract |
This paper surveys the results of our investigation of the microbial diversity and biogeochemistry of some Philippine hot springs. The thermophilic microbial communities inhabiting these springs are of extreme interest for their unique value as potential analogues for EarthÆs earliest life. Anaerobic, acidic, sulfidic, thermal springs represent potentially important settings for the earliest organisms on Earth, and the chemolithotrophs and phototrophs inhabiting them are possible candidates for Earth's earliest sustainable microbial communities. Thermostable enzymes from these thermophilic microbial communities are also of potential biotechnological value, specifically for medicinal and industrial use, hence there is also some practical interest in documenting and characterizing these communities. We are presently examining the connection between biogeochemical cycling of sulfur, carbon and other nutrients and the diversity of metabolic activities in the thermophilic autotrophic communities from several hot springs historically monitored by the Philippine National Oil Company-Energy Development Corporation (PNOC-EDC). We will highlight one particular locality in detail (Lipayo #1, Negros Oriental, Philippines), where we have shown that the gradient of pO2, pH and T is accompanied by consistent changes in the microbial community composition from those dominated by anaerobic, acidophilic and S oxidizing bacteria (e.g., Desulfurella multipotens, Hydrogenobacter acidophilus, Aquificales) to those dominated by cyanobacteria (e.g., Microcystis aerugosa), Cyanidium caldarium (red algae), Deinococcus geothermalis within a 10-meter flow interval. The same interval showed a monotonic decline of H2S and increase in SO4=, fluctuation in S2O3=, and no significant shift in Σ34S of either H2S or SO4=. Despite the predominance of oxygenic photosynthesizers (i.e., cyanobacteria) in these sampled hot springs, the relative values of Σ13C of dissolved inorganic carbon, bulk biomass, and component fatty acids near the hot spring vent area are consistent with the significant presence of organisms that fix carbon using the reverse tricarboxylic acid cycle in these vents. |