Thermophilic anaerobic bacteria which ferment hemicellulose: characterization of organisms and identification of plasmids

Abstract

Seven thermophilic anaerobic bacteria which ferment xylan were isolated from natural geothermal features in the western United States. Typically, these strains were Gram-negative non-sporeforming rods with an unusual double-layered cell wall which resembled that observed in Thermobacteroides acetoethylicus. The strains differed from known thermophilic anaerobes in their ability to utilize a very wide variety of carbohydrates and in their ability to grow in a chemically-defined medium and/or at pH 3.5. Four of the strains contained cryptic plasmids of 1.2 or 1.5 X 10(6) daltons. The taxonomic characteristics of the strains are discussed in terms of their relatedness to those of Thermoanaerobium, Thermoanaerobacter, and Thermobacteroides species.