To address these concerns the team ensured to investigate the presence of the Pseudomonas sp. in both the root and stem/leaves. Furthermore, the team shifted from using a wounding inoculation method to a seed-coating method.

The first set of results came from seed-coating experiments, where 96 Arabdisopsis thaliana seedlings were surface sterilised and coated in a liquid culture of Pseudomonas sp. wild type. Once germinated, 8 seedlings were selected and surface sterilised before being cut at the root and leaves for plating on TSA plates. Wild type Pseudomonas sp. was re-isolated from all of these samples and no Pseudomonas sp. was re-isolated from a set of 8 control Arabidopsis thaliana seedlings. These results showed that seed-coating was an appropriate inoculation method which makes our project more accessible for commercial use.

Figure 1. Pseudomonas sp. on a TSA plate that has been re-isolated from Arabidopsis thaliana seedlings which have been inoculated by the seed-coating method suggested by GrowUp Urban Farms.

Using seedlings inoculated with wild type Pseudomonas sp., DAPI staining and bright field microscopy were used to visualise the relationship between plant and bacteria. This revealed a biofilm was present on the surface of the root however it was unclear if the bacteria was inside the root, so seedlings were washed in distilled water. Examination of the cleaned seedlings revealed clear signs of colonisation and Pseudomonas sp. was present in intercellular spaces along both the root and hypocotyl. The bacteria were still motile and we could see them moving in real time.

Figure 14. Bright field microscopy of a DAPI stained Arabidopsis thaliana root at 40x magnification. Wild type Pseudomonas sp. is visible in the intercellular spaces.

A selection of Pseudomonas sp. transformant-inoculated seedlings were taken for microscopy, again seedlings were washed and DAPI stained.Endophytic bacteria were visible inside the root and hypocotyl of both Arabidopsis thaliana and Eruca sativa seedlings showing that transformation had not altered the bacteria’s ability to colonise.

Figure 21. Bright field microscopy of an Arabidopsis thaliana seedling root at x100 magnification,showing transformed Pseudomonas sp. living as an endophyte in the intercellular spaces.

A selection of seedlings were again selected for microscopy, this time negative control E. coli DH5α inoculated seedlings were examined. Microscopy revealed that though E. coli was present on the root surface, there was no sign of endophytic relationship like that of Pseudomonas sp.. Further images were taken of transformant Pseudomonas sp. inoculated seedlings to aid visual demonstration of our transformed endophyte working.

Figure 23.Bright field microscopy showing the root of our negative control Arabidopsis thaliana at100x magnification, where E. coli DH5α was visible on the surface of the root in small numbers but not inside the root as an endophyte.