HABS-BLOCKS, a floating, slow-release glucose source, promoted the growth of non-toxic heterotrophic bacteria relative to toxic cyanobacteria in lake water mesocosms

Previously, we demonstrated that the addition of glucose to lake water could alter the composition of the microbial community so that heterotrophic bacteria came to dominate the cyanobacteria. To target the glucose additions to the euphotic zone, a floating, slow-release glucose source, designated HABS-BLOCKS, was created. During a ten-week experiment, glucose concentrations were measured and 25 ml samples were obtained from each mesocosm weekly, which were then filtered, frozen and latter processed for 16S rRNA sequencing and qPCR quantification of total cyanobacteria. Glucose concentrations in the HABS-BLOCKS treated mesocosms increased for the first three weeks and then gradually declined becoming undetected at eight-weeks. Cyanobium and Planktothrix were the most abundant cyanobacteria in the lake water. Within three weeks of the start of the experiment, the bacterial community in the HABS-BLOCKS treated mesocosms became dominated by heterotrophic bacteria relative to the Control mesocosms. HABS-BLOCKS do not kill Cyanobacteria, which persisted in both the Treated and Control mesocosms, but rather HABS-BLOCKS appear to provide a competitive edge for the non-toxic heterotrophic bacteria that allows them to dominate the toxic cyanobacteria on a relative basis.