Aciduric Proteobacteria isolated from pH 2.9 soil.

Acidic (pH 2.9) soil was used as an inoculum to culture heterotrophic bacteria at pH values of 3-4. Four isolates were obtained; on the basis of 16S rDNA sequence, they were shown to be members of the beta- and gamma-Proteobacteria. The three isolates that were most closely related to Burkholderia spp. had simple nutritional requirements and could grow in glucose-mineral salts media; two of these used a broad array of organic substrates. The 16S rDNA sequence of the fourth isolate was most similar (96%) to Frateuria aurantia. The isolates were aciduric rather than acidophilic; their pH ranges for growth were approximately 3.5-8. Unlike many bacteria whose acid tolerance represents the capacity to survive acid exposure, these microorganisms carried out exponential growth at pH<4 and their growth rates at pH 3.9 ranged from 60 to 98% of those found at pH 7. The cell yields on glucose of two strains were identical at pH 4 and pH 7. The acidic soils appeared to contain a very diverse bacterial community as assessed by denaturing gradient gel electrophoresis fingerprinting of PCR amplicons of a portion of the 16S rDNA gene. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00203-002-0427-1.