Mechanistic modeling of light-induced chemotactic infiltration of bacteria into leaf stomata.

Light is one of the factors that can play a role in bacterial infiltration into leafy greens by keeping stomata open and providing photosynthetic products for microorganisms. We model chemotactic transport of bacteria within a leaf tissue in response to photosynthesis occurring within plant mesophyll. The model includes transport of carbon dioxide, oxygen, bicarbonate, sucrose/glucose, bacteria, and autoinducer-2 within the leaf tissue. Biological processes of carbon fixation in chloroplasts, and respiration in mitochondria of the plant cells, as well as motility, chemotaxis, nutrient consumption and communication in the bacterial community are considered. We show that presence of light is enough to boost bacterial chemotaxis through the stomatal opening and toward photosynthetic products within the leaf tissue. Bacterial chemotactic ability is a major player in infiltration, and plant stomatal defense in closing the stomata as a perception of microbe-associated molecular patterns is an effective way to inhibit the infiltration. Author summary Exposure to light can trigger photosynthesis in plant leaves, such as leafy-greens, and increase concentrations of photosynthetic products, such as glucose, within the leaf tissue. Bacteria existing at the leaf surfaces may respond to the available photosynthetic products and migrate into the leaf tissue by chemotaxis toward nutrient concentration gradients. Once the bacteria are inside the leaf tissue, they cannot be washed away, presenting a risk to the consumer. Here, a physics-based model for this light-driven infiltration is presented. This mechanistic model couples transport of bacteria and nutrients, and photosynthesis within a leaf tissue around one stomatal opening. The model shows that the ability of bacteria to transport via chemotaxis is a major factor in infiltration. A moderate intensity light is sufficient to promote chemotactic infiltration of bacteria on a leaf surface into its interior. Infiltration is enhanced in the presence of blue, white and red lights, and for a larger stomatal aperture.