Microalgae Cultivation: Nutrients

What are the Key Macronutrients?

Macronutrients are the nutrients that phytoplankton require in the most significant amounts. The ratio between these nutrients is relatively consistent across microalgae and is known as the Redfield Ratio. The Macronutrients consist of a mix of:

• Carbon: the most abundant element in phytoplankton, which we discussed in a previous Algae Growth Series article.
• Nitrogen: Primarily used by phytoplankton to build proteins.
• Phosphorus: This is the least abundant of these three macronutrients, and is mainly used to build nucleic acids (DNA and RNA) as well as lipids (Finkel et al. 2015).

Note: Media recipes for culturing microalgae usually supply these nutrients at levels much higher than those expected in nature to prevent growth limitations.

What are the Recommended Concentrations for Trace Metals?

Many metals are required at low concentrations for microalgae growth. Trace metal solutions are often prepared with EDTA, which binds dissolved metals to prevent them from precipitating. Most common recipes include:

• Iron
• Molybdenum
• Zinc
• Cobalt
• Manganese. 

Note: Other metals may or may not be included depending on the recipe.

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).

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 need it in proportions similar to those of nitrogen (Brzezinski 1985). This is why silicate is added to microalgae culture media when growing diatoms. However, most recipes do not follow a 1:1 ratio with nitrogen. The limitation of these macronutrients is one of the easiest ways to get unreliable algae cultures.

There are many algae media recipes available.  Some considerations about which recipe to use are:

• What strain 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?  

Note: 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.

This article is the fifth of our Microalgae Growth Series. Check out our other posts in the series, including:

• Light Intensity
• Light Spectrum
• Overview of Key Parameters
• CO2 and pH.

Industrial Plankton manufactures and supplies PBRs in 2500L, 1250L, and 100L. Explore algae production equipment here.

Check out our other posts in the series that include: Light Intensity, Light Spectrum, Overview of Key Parameters and CO2 and pH.

References

Algae media recipes. (2020.). Retrieved April 19, 2021, from https://ncma.bigelow.org/algae-media-recipes

Brzezinski, M. A. (1985). The Si: C: N ratio of marine diatoms: interspecific variability and the effect of some environmental variables 1. Journal of Phycology, 21(3), 347-357.

Eighty years of Redfield. Nature Geosci 7, 849 (2014). https://doi.org/10.1038/ngeo2319

Finkel, Z. V., Follows, M. J., Liefer, J. D., Brown, C. M., Benner, I., & Irwin, A. J. (2016). Phylogenetic diversity in the macromolecular composition of microalgae. PLoS One, 11(5), e0155977.

Helliwell, K. E. (2017). The roles of B vitamins in phytoplankton nutrition: new perspectives and prospects. New Phytologist, 216(1), 62-68.