February 14 2023
Macronutrients are those that are required in the greatest amount by phytoplankton. The ratio between these nutrients is fairly consistent across microalgae and is known as the Redfield Ratio.
Carbon is the most abundant element in phytoplankton, which we discussed in a previous Algae Growth Series article. The next most abundant is nitrogen which is primarily used by phytoplankton to build proteins. Phosphorus is the least abundant of these three macronutrients and is used mostly to build nucleic acids (DNA and RNA) as well as lipids (Finkel et al. 2015).
Media recipes for culturing microalgae usually supply these nutrients in much higher quantities than would be expected in nature so that they are not limiting growth.
Most microalgae don’t require silicate to grow but for one group it is essential – the diatoms.
Diatoms use silicon to build their cell walls and require it in similar proportions to nitrogen (Brzezinski 1985). Silicate is added to microalgae culture media when growing diatoms, though most recipes do not follow a 1:1 ratio with nitrogen.
Limitation of these macronutrients is one of the easiest ways to get unreliable algae cultures.
Many metals are required at low concentrations for microalgae growth. Most common recipes include iron, molybdenum, zinc, cobalt, and manganese. Other metals may or may not be included depending on the recipe. Trace metal solutions are often prepared with EDTA, which binds dissolved metals to keep them from precipitating out of the solution.
Just like humans, algae need vitamins they can’t produce themselves; however, unlike us, the vitamin requirements vary across microalgae lineages (Helliwell 2017). The three most common vitamins supplied in algal media are thiamine (B1), biotin, and cyanocobalamin (B12).
There are a vast number of algae media recipes available. Some considerations about which recipe to use are:
- What strain of do you want to grow?
- Does it have specific requirements?
- What do other people growing this strain of algae use? Are their goals the same as yours? Do they use the same PBRs?
- Are you preparing your media from natural seawater, or artificial seawater?
If you are making salt water from reagent-grade salts it is a good idea to follow a recipe that is intended for artificial seawater. These recipes will add more trace elements that would already be present if you were using a natural seawater base.
Check out our other posts in the series that include: Light Intensity, Light Spectrum, Overview of Key Parameters and CO2 and pH.