Ecological assessment and geological significance of microbial communitiesfrom Cesspool Cave, Virginia

Microbial mats from hydrogen sulfide-rich waters and cave-wall biofilms wer e investigated from Cesspool Cave, Virginia, to determine community composi tion and potential geomicrobiological functioning of acid-producing bacteri a. Rates of microbial mat chemoautotrophic productivity were estimated usin g [C-14]-bicarbonate incorporations and microbial heterotrophy was determin ed using [C-14]-leucine incubations. Chemoautotrophic fixation was measured at 30.4 +/- 12.0 ng C mg dry wt(1) h(1), whereas heterotrophic productivit y was significantly less at 0.17 +/- 0.02 ng C mg dry wt(1) h(1). The carbo n to nitrogen ratios of the microbial mats averaged 13.5, indicating that t he mats are not a high quality food source for higher trophic levels. Ribos omal RNA-based methods were used to examine bacterial diversity in the micr obial mats, revealing the presence of at least five strains of bacteria. Th e identity of some of the strains could be resolved to the genus Thiothrix and the Flexibacter-Cytophaga-Bacteriodes phylum, and the identity of the r emaining strains was to either the Helicobacter or Thiovulum group. Two of 10 sulfur-oxidizing, chemoautotrophic pure cultures of Thiobacillus spp. (s yn. Thiomonas gen. nov.) demonstrated the ability to corrode calcium carbon ate, suggesting that the colonization and metabolic activity of these bacte ria may be enhancing cave enlargement.