Genetic Detection of a Novel Geosmin-Producing Oscillatoria lutea Isolated from the Euphrates River, Iraq

Abstract

In freshwater environments, cyanobacteria are responsible for the majority of taste-and-odour compounds that compromise water quality. Geosmin, a widespread bicyclic tertiary alcohol, is one of the most problematic of these compounds, imparting a persistent earthy–musty character to drinking water. Because the timely surveillance of geosmin producers is central to any early-warning system, molecular tools capable of rapidly detecting the responsible organisms offer a practical alternative to conventional taxonomic and instrumental approaches. In the present study, a cyanobacterial strain isolated from the AlShamiya River, a branch of the Euphrates in central Iraq, was characterised morphologically and then confirmed genetically using the 16S rRNA gene. The isolate shared 100% sequence identity with Oscillatoria lutea deposited in the National Center for Biotechnology Information (NCBI) GenBank database. Amplification and sequencing of the geosmin synthase gene revealed 100% identity with the putative geosmin synthase (geoL) gene of Oscillatoria sp. PCC 6506 and progressively lower identity with the homologous gene of other cyanobacteria, reflecting the conserved architecture of the geosmin-biosynthetic machinery. At the amino-acid level, BLAST analysis further demonstrated pronounced homology among taxonomically distant geosmin producers, including actinomycetes, cyanobacteria, fungi and myxobacteria. These findings confirm that genetic analysis is an accurate, inexpensive and rapid means of identifying cyanobacterial species and of predicting the occurrence of taste-and-odour compounds in water resources.