The term bacterial cities means that bacteria and fungi build lives, similar to how humans construct houses, offices, and schools. Bacteria and fungi live in comparable structures, albeit on a much smaller scale and on every surface in the environment. In the past, humans lived in the open field without a roof over their heads, dealing with external stress factors such as rain, storms, or extreme heat.
Therefore, humanity started building wooden barns to protect themselves, and nowadays we build skyscrapers. In this way, humanity can live safely as well as share knowledge and experiences at the office or school. Bacteria and fungi live in similar cities.
The growth and development of biofilm
Bacteria are often the first inhabitants; they attach themselves to a surface (such as the inside of an irrigation system) and create a slimy layer to protect themselves. This layer is largely made up of sugars but also proteins, lipids, and minerals. Once settled, bacteria multiply in the slime layer. Or stated differently, the city expands, and the ‘biofilm’ grows. The biofilm can further develop by spreading a portion of the bacteria (Figure 1), just like children leaving their parental home when they are adults. Thus, once biofilm is present, it will grow and spread exponentially (Karygianni, Ren, Koo, & Thurnheer, 2020; Alotaibi & Bukhari, 2021).
Figure 1: The three stages of biofilm development. Phase 1: Attachment of free-floating bacteria to the surface. Phase 2: A biofilm is formed and grows. Phase 3: Detachment and spreading of bacteria to other surfaces (Karaguler, Kahraman, & Tuter, 2017).
Although biofilm is better resistant to external stressors, factors such as temperature, humidity, oxygen levels, and turbulence still affect the growth and stability of biofilm. For example, a higher temperature increases biofilm's potential to grow and spread. Additionally, greater turbulence (like the flow of water) creates more stress for bacteria, which is a stimulus for forming a thicker layer of biofilm. These mentioned conditions are similar to the environment in irrigation pipes.
The influence of nutrient water
On top of this, minerals are added to the nutrient water for plants to optimize their health and development. However, fertilizers are also beneficial for microorganisms in the biofilm. The minerals from fertilizers are used as food and reinforcement. The minerals act as scaffoldings, making the biofilm stronger and more stable (Figure 2). This makes it harder, but also more dangerous, to remove the biofilm. Once the scaffolds are broken down, the bacterial city collapses, and large parts of the biofilm become detached, which can cause clogged drippers. Therefore, it is essential to be aware of the formation of biofilm in the irrigation system and the necessity to prevent its formation.
Figure 2. Biofilm formation with and without the presence of the mineral calcium. The result is shown after 3 and after 7 days of water flow (Oppenheimer-Shaanan et al., 2016).
Constructive collaboration of fungi and bacteria
Aside from bacteria, fungi also form biofilm structures. Fungi often attach to mature bacterial biofilm. Research has shown that the hyphae of fungi are used by bacteria as a highway. The fungal structures serve as a vector for bacteria spreading and strengthen the formation of biofilm. Once fungi are part of the biofilm, the structure is more resilient and more difficult to remove.
Preventing and removing biofilm
With these threats, it is crucial to prevent the formation of biofilm. When it is already present, it is important to remove it to avoid problems during cultivation. Since biofilm is mainly composed of sugars, it is important to use a product that breaks down and tackles these sugars. Claudia Weick of Intrahorti says: “Often products based on chlorine are used; however, these do not meet this requirement. Intra Hydropure is a silver-chelated hydrogen peroxide. This can tackle the biofilm. It evenly breaks down the biofilm, and the bacteria and fungi that are released are eliminated. This prevents infections in plants and blocked drippers.”
Intra Hydropure is a biocide specifically designed for usage in irrigation systems. The product is registered according to the EU-BPR and is specifically allowed for the removal of biofilm and disinfection. Claudia: “By improving water quality and reducing microbiological contamination, Intra Hydropure is a sustainable solution for hygiene applications in horticulture.”
For more information:
Intrahorti
Voltaweg 4, 5466 AZ
Veghel, the Netherlands
Tel.: +31 (0)413 354 105
info@intrahorti.nl
www.intrahorti.nl