The agarose gel that we rely on to analyze nucleic acids, perform chromatography, and so much more, is derived from a humble sea moss. Overharvesting threatens the future of this natural wonder and scientific resource. Let’s be thankful for the ongoing switch to sustainable production
Red algae
According to a PLOS Biology study, hardy red algae are thought to be the most ancient multicellular organisms on the planet. The fossil record goes back a mind-blowing 1.6 billion years. That’s quite an evolutionary success story when you contrast its harsh growing environment against that of terrestrial plants. Many red algae persevere in the strong physical forces of ocean tides, low availability of nutrients, extreme salinity, varying temperatures, and desiccation between high and low tides. What’s fascinating is that part of their evolutionary resilience can be attributed to the polysaccharide within its double cell walls. Agar enables survival.
From a humble sea moss to a refined reagent
Agar is also a biopolymer with commercial and scientific value. Most agar is extracted from red algae species of Gelidium and Gracilaria primarily for food and fertilizer. Colder seasonal waters produce thicker cell walls which are broken down with a dilute acid solution in a pressure cooker to extract agar. Gelidium species of red algae are preferred for bacteriological and pharmaceutical grade agar due to their naturally strong gelling quality. However, Gracilaria extracted agar can also be used after alkali treatment to “de-kink” the molecules and improve gelling quality.
The main component of agar is agarose, a linear biopolymer of repeating agarbiose units that you probably have at your lab bench right now. Biologists rely on agarose supplies for chromatography, tissue embedding, and especially electrophoresis. Typically agarose resin is mixed in TAE buffer at 1%, then heated until clear, poured into a slab to form the just right matrix at room temp to resolve DNA above 100 bp. Agarose gel matrix pore sizes are larger in lower concentrations. Higher concentrations of agarose gels can improve sample resolution. Agarose gel electrophoresis of nucleic acids became widespread once it was pioneered by molecular biology giant Joseph Sambrook and colleagues at the Cold Spring Harbor Laboratory in 1973. See: P A Sharp, B Sugden, J Sambrook Detection of two restriction endonuclease activities in Haemophilus parainfluenzae using analytical agarose--ethidium bromide electrophoresis (1973) Biochemistry. Later electron microscopy studies confirmed that agarose gels accurately reflected DNA molecular mass, while the mobilities observed in polyacrylamide gels did not. This is all to say that molecular biology owes much to red algae.
Agar shortages and sustainability
Harvesting wild red alga is problematic. The situation came to a head in 2015 when Gelidium spp. was over-harvested from sea beds in Japan, Morocco, and Chile. This led to forced supply shortages of microbiology-grade agar as shared in Nature. Since then researchers have worked to analyze this issue and suggest eco-friendly solutions.
Happily, sustainability is now the mantra for the seaweed industry. Wild harvesting is being replaced by red seaweed crops cultivated around the world in bays, estuaries, reef flats, and ponds, on lines, ropes, or nets. New and improved agarose extraction and purification methods have been developed to green manufacturing. Large industrial producers like Cargill and Hispanagar continue to target internal and partner sustainability.
The good news is that sustainable aquaculture is working. An effervescent review by The Nature Conservatory in June 2021 confirmed that restorative aquaculture has positive impacts on marine life. While many biology labs are experiencing supply chain delays, sustainable production is expanding. Aquaculture of agarose-yielding red alga is being investigated on the Gujarat coast of India and other parts of the world. When biologists are unencumbered by ecological threats and able to focus on developing exciting new applications in biofuel, carbon biofixation, and bioplastics everyone can benefit from advances.
So today and each time we use agarose in the lab - we can be thankful to the farmers, marine biologists, ecologists, chemists, and manufacturers for their collaborative push for red seaweed sustainability!