Construction of a reporter plasmid for monitoring of geoA regulation in Myxococcus virescens during predation.

Geosmin is a volatile, earthy-smelling metabolite produced by various microbial taxa, including myxobacteria. In aquaculture, geosmin can cause off-flavor in fish, with great impact on fish quality. However, insight into geosmin's ecological role remains limited, and the environmental conditions that trigger the expression of the geosmin synthase gene (geoA) are uncertain. Here, we introduce a fluorescence-based (mCherry) reporter assay as a tool to measure the promoter activity of the geoA gene in Myxococcus virescens AT3, a strain previously isolated from a commercial fish farm in Denmark. The transformed M. virescens AT3 strain displayed fluorescence when grown in pure culture, and was used to visualize geoA expression activity during interactions with Streptomyces sp. and Pseudomonas sp., which served as prey bacteria. The bioreporter strain provides new insights into the biotic and abiotic factors that influence geosmin production in Myxococcus.