Diverse, yet-to-be-cultured members of the Rubrobacter subdivision of the Actinobacteria are widespread in Australian arid soils

Phylogenetic analyses of ribosomal RNA gene sequences (rDNAs) retrieved fro m an Australian desert soil sample (Sturt National Park) revealed the prese nce of a number of clones which branched deeply from the high GC Gram-posit ive division line of descent. The most abundant group of these clones were related to Rubrobacter. An oligonucleotide probe was designed to have broad specificity to Rubrobacter and relatives. This probe was used to interroga te eight rDNA libraries representing four distinct land forms within the Au stralian arid zone. Relative abundance of Rubrobacter-relatives in these sa mples ranged from 2.6 to 10.2%. Clones from these Libraries were selected f or sequence analysis on the basis of a heteroduplex mobility assay to maxim ise the diversity represented in the sample. Phylogenetic analyses of these rDNA clones and Rubrobacter-related clones reported in the literature show strong support for three distinct groups. Database-searching revealed 'Rub robacteria' were relatively abundant in a number of published soil rDNA lib raries but absent from others. A PCR assay for group-1 'Rubrobacteria' was used to test for their presence in 21 environmental samples. Only marine an d arid-zone soil samples gave positive PCR results. Taken together these re sults indicate 'Rubrobacteria' are a widespread group of variable abundance and diversity. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.