Theo Dreher | Geology Reports

USGS2025

Dominant Dolichospermum and microcystin production in Detroit Lake (Oregon, USA)

The excessive growth of harmful cyanobacteria, including Dolichospermum (formerly known as Anabaena ), in freshwater bodies has become a pressing global concern. However, detailed information about the role of Dolichospermum in shaping bloom dynamics and producing cyanotoxins is limited. In this study, a bloom event dominated by Dolichospermum spp. at Detroit Lake (Oregon, USA) was examined from 2019 to 2021. In 2019, early summer cyanobacterial community succession reached up to 8.7 % of total phytoplankton abundance. Dolichospermum was the major microcystin (MC)-producing genus, with peak MC levels of 7.34 μg L −1 . The presence of MCs was strongly correlated with the abundance of Dolichospermum ( r = 0.84, p < 0.05) and MC synthetase gene, mcyE-Ana ( r = 0.63, p < 0.05). Metabolic analyses further showed that the presence of nif / pst genes linked to nitrogen and phosphorus metabolism was dominated by Dolichospermum from the bloom onset until September. In addition, the abundance of Dolichospermum was significantly correlated with the abundance of nitrogen-fixing nif-Ana gene ( r = 0.62, p < 0.05). As the lake experienced a longer N and P scarcity period (May to September), the N 2 -fixing Dolichospermum was able to dominate over other non-fixing cyanobacteria present, including Microcystis and Planktothrix . Overall, our results facilitate a better understanding of the organism and will help working toward managing/predicting future blooms.

Oregon↗

USGS2016

Elucidation of taste- and odor-producing bacteria and toxigenic cyanobacteria in a Midwestern drinking water supply reservoir by shotgun metagenomics analysis

While commonplace in clinical settings, DNA-based assays for identification or enumeration of drinking water pathogens and other biological contaminants remain widely unadopted by the monitoring community. In this study, shotgun metagenomics was used to identify taste-and-odor producers and toxin-producing cyanobacteria over a 2-year period in a drinking water reservoir. The sequencing data implicated several cyanobacteria, including Anabaena spp ., Microcystis spp ., and an unresolved member of the order Oscillatoriales as the likely principal producers of geosmin, microcystin, and 2-methylisoborneol (MIB), respectively. To further demonstrate this, quantitative PCR (qPCR) assays targeting geosmin-producing Anabaena and microcystin-producing Microcystis were utilized, and these data were fitted using generalized linear models and compared with routine monitoring data, including microscopic cell counts, sonde-based physicochemical analyses, and assays of all inorganic and organic nitrogen and phosphorus forms and fractions. The qPCR assays explained the greatest variation in observed geosmin (adjusted R 2 = 0.71) and microcystin (adjusted R 2 = 0.84) concentrations over the study period, highlighting their potential for routine monitoring applications. The origin of the monoterpene cyclase required for MIB biosynthesis was putatively linked to a periphytic cyanobacterial mat attached to the concrete drinking water inflow structure. We conclude that shotgun metagenomics can be used to identify microbial agents involved in water quality deterioration and to guide PCR assay selection or design for routine monitoring purposes. Finally, we offer estimates of microbial diversity and metagenomic coverage of our data sets for reference to others wishing to apply shotgun metagenomics to other lacustrine systems.

Kansas↗