Identification and Expression Analyses of Putative Sesquiterpene Synthase Genes in Phormidium sp. and Prevalence of geoA -Like Genes in a Drinking Water Reservoir

The occurrence of taste and odor problems in drinking water supplies is a widespread phenomenon. From a Saxonian water reservoir we isolated a cyanobacterial species which was classified asPhormidium sp. Under laboratory conditions it produced an earthy-musty smell due to the synthesis of geosmin. The only genes shown to be involved in geosmin biosynthesis arecyc2 andgeoA ofStreptomyces . Based on the alignment of Cyc2 with a putative sesquiterpene synthase ofNostoc punctiforme , a degenerate primer pair was designed. By PCR, we could amplify two similar genes inPhormidium sp., which we namedgeoA1 andgeoA2 . Their expression was studied by reverse transcription-PCR. This revealed that both genes are expressed at 20°C and a light-dark cycle of 12 h. Expression was not detectable at the end of a 24-h dark period. To analyze the prevalence ofgeoA1 andgeoA2 in samples from the phytobenthos, we generated PCR fragments with the same degenerate primer pair. Fifty-five different sequences that might representgeoA variants were obtained. The GC content ranged from 42% to 67%, suggesting that taxonomically very different bacteria might contain such genes.