Endospore formation by Streptomyces avermitilis in submerged culture

Distribution, abundance and activity of geosmin and 2-methylisoborneol-producing Streptomyces in drinking water reservoirs

While cyanobacteria have been widely recognised as the most common cause of geosmin and 2-methylisoborneol related taste and odour (T&O) episodes in drinking water supplies, many reported occurrences could not be attributed to these organisms. The Streptomyces genus of soil bacteria also includes producers of these compounds, however their potential role in such occurrences is poorly understood and often disregarded on the basis that they are terrestrial rather than aquatic organisms, with their detection in water samples assumed to reflect the presence of dormant spores rather than metabolically active vegetative cells. Using qPCR and a differential cell lysis technique for DNA extraction, allowing distinction of spores from vegetative cells, the aim of this study was to determine the distribution, abundance and potential activity of Streptomyces species across a range of aquatic and marginal habitat zones in two drinking water reservoirs, including: exposed soil, submerged sediments, plant debris and emergent macrophytes at the margins; marginal and offshore surface waters; deep offshore waters; and offshore benthic sediments. Marginal substrates including soil, sediment and plant debris were identified as the dominant habitat zones for Streptomyces, (concentrations up to 1.1 × 10⁷ cells g^-1) supporting the concept of 'wash-in' from the margins due to run-off or water level rise following rainfall, as the likely pathway for Streptomyces induced T&O in reservoirs. However, vegetative cells were also found to comprise a substantial proportion of Streptomyces populations in the reservoir water mass itself (>90% in some surface and bottom water samples), suggesting the potential for these bacteria to be metabolically active in the water and therefore contribute to in situ production of T&O metabolites.