Cultivation of Hydrogen-Consuming Microbes from Anaerobic, Xyloglucan-Degrading Thermophilic Consortia

Event Center A & B

Degradation of plant polymers at high temperatures remains poorly understood and, although they may have potential uses in secondgeneration biofuels, many microbes in thermophilic, hemicellulose-degrading consortia represent novel lineages that have yet to be described. Isolation of hydrogen-consuming microbes, including members of the genera Archeaglobus or Thermodesulfobacterium, was attempted on laboratory enrichments originally obtained from hot springs in Nevada using xyloglucan as a sole carbon source. Several isolates were obtained by plating the enrichments on solid, anaerobic minimal media with hydrogen gas in the headspace, designed to isolate hydrogen-consuming members of Archeaglobus or Thermodesulfobacterium using sulfate, sulfite or thiosulfate as terminal electron acceptros. A member of the genus Thermodesulfobacterium was isolated and may represent a novel species, with 98.7% rRNA gene identity to T. hveragerdense. Two additional isolates were identified as members of the genera Dictyoglomus and Thermotoga, and were closely related to describe species that are obligate organotrophs. Because these isolates could not grow in liquid media without complex organic substrates, they likely were utilizing the solidification agent or trace organics in the solid medium. To circumvent this problem, additional isolation attempts were performed in liquid media using the dilution-to-extinction method, where 10-3 to 10-9 dilutions of the inoculate were made into appropriate liquid medium. Dilutions were checked for growth by microscopy; once growth was observed a repeated series of dilutions throughout a time of three weeks was performed. DNA extraction, amplification and sequencing of 16S rRNA genes will be used to determine if pure cultures were obtained.