## 4 Discussion  
Application of plasma in food industry is becoming increasingly important. Due to the promising application possibilities of PGCs, several studies are currently in progress, which can be summarized under the collective term \"Plasma for Food\" [33; 34; 35]. This term covers a broad spectrum from pre- and postharvest, up to the treatment of food with plasma or the packaging materials, in which the food is transported and stored, as well as the treatment of different surfaces which are important in the food production environment [36; 37; 38; 39]. There are two particularly important aspects to get this new innovative method into practical use in the food industry. The first one is that the mechanisms leading to the inactivation of spoilage organisms by plasma treatment are clarified [40; 41; 42]. On the other hand, the plasma technology has to be further upscaled to huge product turnovers and consumption of industrial goods like water in order to meet the requirements of the food industry [43]. Therefore, it is important to identify the mechanisms of PGCs on microorganisms such as _P. fluorescens_ that cause significant problems in the food industry. _P. fluorescens_ is able to form biofilms on surfaces relevant in the food industry like stainless steel, Polyethylene terephthalate (PET) or Teflon [8; 44] as well as on the food products itself [5]. It produces fibrillary structures as a matrix for the biofilm. This matrix seems to be 2-3 times smaller than the actual bacteria packed in unknown extracellular structures [45]. These fibrillary structures were also macroscopically recognizable in comparison to biofilms of other species and seem to contribute to the physical properties of the biofilm. Due to these structures, the biofilms of _P. fluorescens_ tend to be mechanically washed away during treatment with PTW. Because of the flow properties of PTW, larger cell masses were washed away during pipetting on the biofilm by these connected fibrillary structures. This, in turn, explains the large gaps in control biofilms in CLSM and fluorescence microcopy (Figures 4A and 5A). The AFM images of the control biofilms also showed an extremely soft surface, resulting in the cantilever of the AFM hardly being able to generate images of the control biofilms and creating long stretched artifacts on the surface (Figure 6A). In comparison, the treated biofilms could be measured much more easily, which suggests a change in the plasticity of the cells may be due to the loss of fluidity. Macroscopically, the treated biofilms appeared whitish and dry, which is why they have changed their physical properties into a solid cell layer. As a result, as soon as enough force was applied to release the biofilm, the entire biofilm was detached as a uniform layer, whereas in control biofilms only biofilm segments were detached and the coarse cell mass remained. This behavior of the control biofilms is naturally favored, since the detached cell mass is transported from the site  
Figure 6: Atomic force microscopy (AFM) images of _P. fluorescens_ biofilms. Left) topographical images right) error images. The pretreatment time defines the time period in which the water came into contact with the plasma gas. The post-treatment time represents the period of time, where the PTW came into contact with the biofilm. (**A**) Control biofilm (**B**) 100 s pretreatment, 5 min post-treatment (**C**) 300 s pretreatment, 5 min post-treatment, 5 min post-treatment (**D**) 900 s pretreatment, 5 min post-treatment. of infection to other areas, e.g., during manifestation in a living organism like humans, in order to recolonize the new areas [46; 47; 48; 49]. This happens in the same way in industrial plants. As an equivalent to the blood flow in living organisms, the wash water in the production plant is used, which removes biofilm mass and transports the biofilm particles to other areas of the facility, where it leads to new biofilm colonization [50; 51]. This study showed a clear effect of PTW on the _P. fluorescens_ biofilms.