In an attempt to confirm purple light is optimal wavelength for growing Rocket we ran a simple experiment. Using off cut ply wood we created a barrier which was placed inside the hydroponics effectively blocking the light. This allowed us to programme the Arduino to emit green and purple light independently, the light intensities were measure at 200, 1700 Lux respectively (code can be found here). Seeds were then placed in two 96 well racks, one green (A), one purple (B). They were then left to germinate for a week.

It was expected that there would be more germinations from rack B, and from the photos below we can see a comparison from racks A and B; 6, 22 respectively. However the shoots in A are significantly taller as they are straining for light. Whereas the Rocket in rack B is more uniform.

As proof of concept, the project aimed to introduce a plasmid containing an operon for naringenin biosynthesis. Naringenin belongs to a group of chemicals named flavonoids which play an important role in plant-microbe interactions.

Through the introduction of said plasmid into our root-colonising Pseudomonas sp. chassis, it was hypothesised that the a microbial community could be engineered. This would be done by attracting selected free-living nitrogen fixing bacteria (FLNFB) in order to localise nitrogen fixation around the root. As a result of this, one would be able to alleviate the over usage of synthetic fertilisers which have numerous detrimental impacts on the environment, ranging from eutrophication [1] to degradation of soil health [2].

We selected Azorhizobium caulinodans (ORS571), Azospirillum brasilense (SP245), and Herbaspirillum seropedicae (Z67) as our FLNFB as they each form different interactions with plant roots. For example, A. caulinodans has been shown to fix nitrogen when free living and when in symbiosis with Sesbania rostrata, a semi-aquatic tree [3]. H. seropedicae on the other hand is a root endophyte, much like our Pseudomonas spp. and commonly colonises popular crops such as wheat and maize [4].

These bacteria provide potential to provide nitrogen nourishment in different ways. However, for the proof of concept, it was important to demonstrate that bacterial behaviour could be influenced by naringenin exposure. As such, a series of assays regarding naringenin’s ability to engineer a microbiome were a core aspect of our project.