Metagenomic analysis of the 1-aminocyclopropane-1-carboxylate deaminase gene (acdS) operon of an uncultured bacterial endophyte colonizing Solanum tuberosum L

Deamination of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is a key plant-beneficial trait found in many plant growth-promoting bacteria. In this study, we analysed ACC deaminase genes (acdS) of bacterial endophytes colonizing field-grown potato plants. PCR analysis revealed the presence of two types of acdS genes, the dominant one showing high homology to an acdS gene derived from Pseudomonas fluorescens. Construction, functional screening and sequence analysis of metagenomic libraries revealed clones containing the acdS gene identified in the PCR library. Sequence analysis of one metagenomic clone identified the entire acdS operon of an uncultivated endophyte and revealed that the acdS gene is coupled upstream with an acdR transcriptional regulator gene as previously found in P. putida strain UW4 (Grichko and Glick 2000). However, in-silico analysis of 195 fully sequenced, acdS-containing bacterial genomes revealed that the majority of strains, including numerous strains belonging to the genus Pseudomonas, do not contain an acdR regulatory gene in the vicinity of the acdS gene or elsewhere in the genome. The acdR (+)-acdS (+) operon was exclusively found in several Alpha- and Betaproteobacteria most prominently in the genus Burkholderia.