Detection of Actinobacteria cultivated from environmental samples reveals bias in universal primers

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Abstract
The aims of this study were to develop media to cultivate actinomycetes, screen the resulting isolates with Actinobacteria-specific primers, and examine the efficacy of detection of the actinobacterial isolates with universal primers. Soil-extract medium was developed for a terrestrial bluff environment. Recovered isolates were subjected to polymerase chain reaction (PCR) with taxon-specific primers to identify Actinobacteria. Universal bacterial primers 24f and 1492r (modified and original versions) were used to amplify the 16S rRNA gene from the putative Actinobacteria. While both reverse primers failed to provide amplification products from 20% to 50% of the isolates, the 1492r primer detected Actinobacteria more effectively than 1492r-mod. The region of the gene containing the annealing site for the 1492r primers from 15 isolates that failed to amplify showed no differences in nucleotide sequence to the original 1492r primer. Universal 16S rRNA gene primers are not capable of amplifying this gene from all bacteria within an environmental sample. Some Actinobacteria may share 100% sequence similarity to universal primers but remain undetected. These findings are important for studies of particular taxa in environmental samples where reactions utilizing universal primers may not reveal the extent of their presence and diversity.

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