Biofilms are slimy layers of microbial colonies that form where microorganisms grow and reproduce. Because microorganisms flourish where water and nutrients are abundant, irrigation systems offer ideal environments for biofilms. When biofilms develop in grow operations, they can create clogs, harbor pathogens and cause oxygen levels in the nutrient solution to drop. Preventing or eliminating biofilms is essential to growing healthy, high-yield crops.
How biofilms develop
Biofilm begins when free-floating microorganisms in the water supply such as bacteria, fungi, protozoa or algae attach to a surface. This is possible through the excretion of an extracellular polymeric substance (EPS), a strand-like structure of polysaccharides that adheres to the surface and to one another.
Eventually, the microbes develop a matrix layer of EPS, which protects and stabilizes the microbial community. As the biofilm matures, it becomes a three-dimensional structure, growing and releasing new bacterial cells which, in turn, initiate new biofilm formations.
Biofilms can form on various substrates under aquatic and terrestrial conditions, but they are site-specific and need the right environmental conditions. Water composition, temperature, pH and flow rate all influence the formation and growth of biofilms in irrigation pipes. The presence of organic matter and nutrients, such as carbon, phosphorus and nitrogen, can also promote the development of microorganisms and contribute to biofilm formation.
How biofilms hurt cannabis grow ops
The most obvious challenge is that once biofilms grow large enough, they can clog components like emitters, filters and valves. Clogs prevent the even distribution of water and nutrients, which can lead to input waste and negatively impact plant growth and yield.
Biofilms can also deoxygenize water. Most of the species present in biofilms are aerobic and need oxygen, which they take from the water. This not only reduces the oxygen plant roots rely on for their survival, but also creates the perfect conditions for harmful anaerobic pathogens, including those that infect plants.
Fusarium is a fungus that cannabis growers often contend with, and many microorganisms in the Fusarium genus have been reported to grow in biofilms.[1] Biofilms are also known to harbor waterborne pathogens like Phytophthora and Pythium. In fact, research suggests that at least two-thirds of waterborne pathogens thrive in biofilms.[2]
[1] Peiqian, Li, Pu Xiaoming, Shen Huifang, Zhang Jingxin, Huang Ning, and Lin Birun. “Biofilm Formation by Fusarium oxysporum f.sp. cucumerinum and susceptibility to environmental sstress.” FEMS Microbiology Letters 350, no. 2 (November 21, 2013): 138–45. https://doi.org/10.1111/1574-6968.12310.
[2] Zylstra, Al. 2014 “You’ve Got Biofilm.” GrowerTalks, March 26, 2014. https://www.growertalks.com/Article/?articleID=20666
Preventing and controlling biofilms
Water is usually the source of biofilm in a cannabis grow operation. Unfortunately, even the cleanest water sources are susceptible to it. The best way to prevent and control biofilms is by treating the water, which growers can do by either oxidizing it, disinfecting it or applying enzymes.
Oxidation kills microbes in the water through cell lysis, a process that breaks cells down by damaging their outer membranes. There are several options for oxidizing water:
- Detergents use oxidizing agents such as chlorine and hydrogen peroxide to oxidize water, but they require emptying and cleaning the entire irrigation system. Growers also need to give the system time to dry and ensure that no residue remains. Otherwise, they could harm the beneficial bacteria in the plant roots:
- Bleach (chlorine) on its own can be used to treat biofilms. However, due to the hydrophobic[1] nature of biofilm, bleach is not the most effective option.
- Hydrogen peroxide on its own can also be effective in combatting biofilms and preventing clogs, and it has the added benefit of oxygenating the water. However, hydrogen peroxide breaks down quickly and does not stay effective for long, which may limit its ability to kill all the microbes found in biofilms.
- Aqueous ozone is a potent sanitizing agent that can eliminate biofilm by oxidizing its cells. It has a short residual time and leaves additional oxygen. However, it requires the use of an ozone generator. Moreover, if not properly monitored, it can deplete certain micronutrients from the nutrient solution. Read our white paper on using ozone in hydroponics.
- Nanobubbles are tiny gas bubbles that destroy existing biofilms and prevent new biofilm formation.
Aside from oxidation, growers can disinfect their water supply using UV radiation, which kills biofilm-forming microbes by destroying their DNA.
Another option is enzyme-based cleaners. Enzymes are proteins that serve as biocatalysts which target specific processes. Anti-biofilm enzymes target the microbial cells in the biofilm matrix, primarily the EPS. They break down the cell-to-cell linkages in the EPS by separating the cells, degrading the macromolecules of the matrix and accelerating the disintegration of biofilm. Check back soon for an upcoming blog post all about enzyme-based cleaners.
[1] Hydrophobic molecules are repelled from water.
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The Emerald Harvest Team
