Abstract
<p>Photosynthetic microorganisms are key primary producers in marine, freshwater and terrestrial environments (Domozych et al, 2012) and have become increasingly important in genomic research, with applications in biofuel production, carbon capture, and wastewater treatment (Sorokin et al, 2026). However, obtaining high-quality DNA from microalgae and cyanobacteria remains challenging due to the presence of rigid cell walls and a wide variety of intracellular and extracellular compounds such as pigments and complex polysaccharides (Eland et al., 2012). These difficulties are more notable in cyanobacteria because several species produce extracellular polysaccharide layers that generate large amounts of cellular debris during DNA extraction (Hept and Greene, 2023). To address these limitations, this protocol describes a modified version of the protocol designed by Hept and Greene (2023). The main modifications to the protocol described by Hept and Greene involve adjustments to both culture volume, reagent usage, and using a cheaper kit Wizard‱ Genomic DNA Purification Kit (A1120), instead of the Wizard‱ HMW DNA Extraction Kit (A2920). Our approach significantly reduces the required volume of cell culture, reducing time and costs, but keeping a good yield of DNA. These changes minimize or completely prevent the formation of the mucilaginous layer for cyanobacteria. The extractions were made on the cyanobacterial strains M. aeruginosa PCC 7806, S. elongatus PCC 7942 and microalgal strains C. reinhardtii CC-1690 and S. dimorphus UTEX417. These organisms were selected because of their widespread use as model organisms in studies of experimental evolution (Figueroa-Gonzalez et al., 2026; Rouco et al., 2011; Sandrini et al., 2016), photosynthesis (Meng et al., 2025; Quevarec et al., 2026), biotechnology (Bühler and Lindberg, 2023; Barbosa et al., 2023). In conclusion, the modified METIS protocol is a simple, reproducible, and efficient method for extracting large amounts of non-fragmented DNA from cyanobacteria and microalgae. The modifications introduced improve DNA recovery while minimizing the interference caused by mucilaginous cellular debris. Despite RNA contamination seen on gels and during NanoDrop quantification, the protocol consistently produces DNA with low fragmentation and concentrations suitable for downstream molecular applications such as PCR and sequencing.</p>