Filamentous cyanobacteria growth assessment using fluorinated ethylene propylene microcapillaries

Filamentous cyanobacteria originate toxic harmful algal blooms (HABs) in aquatic ecosystems, severely impacting freshwater ecosystems and life. Despite being natural bloomers, these microorganisms are challenging to handle in vitro, due to the formation of aggregates with entangled filaments. Consequently, their precise growth dynamics, although vital to timely predict HABs, remains inaccessible. Here, we precisely assessed growth of the HAB forming cyanobacteria Oscillatoria nigroviridis, by cultivating filament suspensions in transparent, gas permeable, and portable fluoropolymer microcapillary strips. Direct optical observation of O. nigroviridis growth revealed shorter filaments comprising less than 50 cells grew at a slower rate, dN/dt = 0.09 cell/day compared to filaments comprising more than 50 cells, with dN/dt up to 0.47 cell/day. The fourfold increase in dN/dt is suggested as part of the blooming strategy of the microorganism. This work suggests that fluoropolymer microcapillary strips can be used for effortless sampling and high-resolution monitoring of HABs. Impact statement: Climate change is increasing the occurrence of episodes of harmful algal bloom, where uncontrolled growth of noxious cyanobacteria such as Oscillatoria species has detrimental outcomes in both the environment and biomass production industry, consequently, impairing human and animal health due to the production of toxic or bioactive compounds. In particular, the study of growth dynamics of Oscillatoria species has been limited to unprecise methods due to complications with aliquoting filamentous biomass. Fluoropolymer microcapillary strips provide an ideal miniaturized platform for sampling, cultivation, and growth monitoring of O. nigroviridis strain UHCC 0327, which paves the way to foster better water quality management tools. Graphical abstract: (Figure presented.)