Ecological Assessment and Geological Significance of Microbial Communities from Cesspool Cave, Virginia

Abstract

Microbial mats from hydrogen sulfide-rich waters and cave-wall biofilms were investigated from Cesspool Cave, Virginia, to determine community composition and potential geomicrobiological functioning of acid-producing bacteria. Rates of microbial mat chemoautotrophic productivity were estimated using [ 14 C]-bicarbonate incorporations and microbial heterotrophy was determined using [ 14 C]-leucine incubations. Chemoautotrophic fixation was measured at 30.4 - 12.0 ng C mg dry wt -1 h -1 , whereas heterotrophic productivity was significantly less at 0.17 - 0.02 ng C mg dry wt -1 h -1 . The carbon to nitrogen ratios of the microbial mats averaged 13.5, indicating that the mats are not a high quality food source for higher trophic levels. Ribosomal RNA-based methods were used to examine bacterial diversity in the microbial mats, revealing the presence of at least five strains of bacteria. The identity of some of the strains could be resolved to the genus Thiothrix and the Flexibacter - Cytophaga - Bacteriodes phylum, and the identity of the remaining strains was to either the Helicobacter or Thiovulum group. Two of 10 sulfur-oxidizing, chemoautotrophic pure cultures of Thiobacillus spp. (syn. Thiomonas gen. nov.) demonstrated the ability to corrode calcium carbonate, suggesting that the colonization and metabolic activity of these bacteria may be enhancing cave enlargement.

Keywords:

• Chemoautotrophy Microbial Mats Primary Productivity Speleogenesis Sulfur Bacteria Thiobacillus Thiomonas Thiothrix