BIODIVERSITY WITHIN HOT-SPRING MICROBIAL MAT COMMUNITIES - MOLECULAR MONITORING OF ENRICHMENT CULTURES

We have begun to examine the basis for incongruence between hot spring microbial mat populations detected by cultivation or by 16S rRNA meth ods. We used denaturing gradient gel electrophoresis (DGGE) to monitor enrichments and isolates plated therefrom. At near extincting inoculu m dilutions we observed Chloroflexus-like and cyanobacterial populatio ns whose 16S rRNA sequences have been detected in the 'New Pit' Spring Chloroflexus mat and the Octopus Spring cyanobacterial mat. Cyanobact erial populations enriched from 44 to 54 degrees C and 56 to 63 degree s C samples at near habitat temperatures were similar to those previou sly detected in mat samples of comparable temperatures. However, a low er temperature enrichment from the higher temperature sample selected for the populations found in the lower temperature sample. Three Therm us populations detected by both DGGE and isolation exemplify even more how enrichment may bias;our view of community structure. The most abu ndant population was adapted to the habitat temperature (50 degrees C) , while populations adapted to 65 degrees C and 70 degrees C were 10(2 )- and 10(4)-fold less abundant, respectively. However, enrichment at 70 degrees C favored the least abundant strain. Inoculum dilution and incubation at the habitat temperature favored the more numerically rel evant populations. We enriched many other aerobic chemoorganotrophic p opulations at various inoculum dilutions and substrate concentrations, most of whose 16S rRNA sequences have not been detected in mats. A co mmon feature of numerically relevant cyanobacterial, Chloroflexus-like and aerobic chemorganotrophic populations, is that they grow poorly a nd resist cultivation on solidified medium, suggesting plating bias, a nd that the medium composition and incubation conditions may not refle ct the natural microenvironments these populations inhabit.