TEMPERATURE-DEPENDENT ENUMERATION AND CHARACTERIZATION OF ANAEROBIC, THERMOPHILIC XYLAN-DEGRADING BACTERIA PRESENT IN 2 ICELANDIC HOT-SPRINGS

Anaerobic thermophilic xylan-degrading bacteria present in unenriched and enriched 70-degrees-C samples from two Icelandic hot springs were enumerated at 68, 78, 90 and 99-degrees-C by the use of the Most-Proba ble-Number method. Xylan was used as substrate. From the samples taken at 70-degrees-C and incubated at the temperatures previously describe d no growth was observed above 78-degrees-C. A total of ten strains we re isolated and characterized from the positive MPN enrichment culture s from the MPN experiments. A higher number of different Strains could be isolated in the enriched samples compared with the unenriched, con trol samples from the same hot spring. Introduction of xylan, i.e., in situ enrichment, into one of the hot springs changed the bacterial po pulation, as none of the bacteria isolated from the unenriched samples were isolated from the enriched samples. All the isolated bacteria we re asporogenous, non-motile and gram-negative rods. One long thin rod had morphological similarities to members of the genus Dictyoglomus an d was found in both hot spring samples.