Cyanobacteria Growth Assessment using Fluorinated Ethylene Propylene Microcapillaries

Due to global warming and other human-derived nutrient rich discharge, nutrient availability increases, causing anomalous proliferation of bloom-forming phytoplankton. This leads to eutrophication and the deoxygenation of bottom waters, with a dramatic toll on the affected food web and ecosystems. Cyanobacteria, also known as blue-green algae, are the main bloomers in freshwater ecosystems, including species of <i>Oscillatoria</i>, known to produce algal toxins with an unpleasant earthy/moldy taste and odor, contaminating water sources and drinking waters.<br/>The study of filamentous cyanobacteria is hampered by technical problems stemming from the slow growth observed <i>in vitro</i>, even with nutrient-rich culture media. Their maintenance in laboratory conditions is demanding and requires frequent nutrient refreshing to prevent culture loss. Moreover, the conventional methodologies used to study growth over time, such as cell counting, are not applicable due to cells being packed into filamentous morphology. Also, dry weight estimations are inconsistent due to the presence of various filament sizes in culture.<br/>To overcome the technical limitation of assessing the filamentary growth of cyanobacteria, we developed a transparent fluorinated ethylene propylene (FEP) microcapillary strips to sample, cultivate and monitor the loaded filaments of <i>Oscillatoria</i> over time.<br/>Geosmin producer strain <i>Oscillatoria </i>sp. UHCC 0332 was cultivated in BG11 medium during 3 weeks, in a growth chamber. Filaments were dip-loaded into 3 cm long strips that were then cultivated in standard conditions for 2 weeks for image assessing and then up to 15 more weeks for confirming survival. The growth of two filaments was determined after 1 and 2 weeks. The estimation of growth was achieved by determining the area occupied by the filaments over time, with image analysis. This enabled the observation that filaments elongate over time with growth rates reaching up to 0.40 day^-1. Also, it was possible to estimate the number of cells which corresponded to elongation. Our microanalytical solution enables long-term micro-cultivation and individual <i>Oscillatoria</i> monitoring over time, which may pave the way to pioneering biocompatible materials for water management and productivity assessment.