DISTRIBUTION OF CULTIVATED AND UNCULTIVATED CYANOBACTERIA AND CHLOROFLEXUS-LIKE BACTERIA IN HOT-SPRING MICROBIAL MATS

Oligodeoxynucleotide hybridization probes were developed to complement specific regions of the small subunit (SSU) rRNA sequences of cultiva ted and uncultivated cyanobacteria and Chloroflexus-like bacteria, whi ch inhabit hot spring microbial mats. The probes were used to investig ate the natural distribution of SSU rRNAs from these species in mats o f Yellowstone hot springs of different temperatures and pHs as well as changes in SSU rRNA distribution resulting from 1-week in situ shifts in temperature, pH, and light intensity. Synechococcus lividus Y-7c-s SSU rRNA was detected only in the mat of a slightly acid spring, from which it may have been initially isolated, or when samples from a mor e alkaline spring were incubated in the more acid spring. Chloroflexus aurantiacus Y-400-fl SSU rRNA was detected only in a high-temperature mat sample from the alkaline Octopus Spring or when lower-temperature samples from this mat were incubated at the high-temperature site. SS U rRNAs of uncultivated species were more widely distributed. Temperat ure distributions and responses to in situ temperature shifts suggeste d that some of the uncultivated cyanobacteria might be adapted to high -, moderate-, and low-temperature ranges whereas an uncultivated Chlor oflexus-like bacterium appears to have broad temperature tolerance. SS U rRNAs of all uncultivated species inhabiting a 48 to 51 degrees C Oc topus Spring mat site were most abundant in the upper 1 mm and were no t detected below a 2.5-to 3.5-mm depth, a finding consistent with thei r possible phototrophic nature. However, the effects of light intensit y reduction on these SSU rRNAs were variable, indicating the difficult y of demonstrating a phototrophic phenotype in light reduction experim ents.