Exploiting bacteriocins as a prophylactic and preventative measure against Potato Blackleg Disease

Blackleg disease and soft rots caused by Pectobacterium atrosepticum (Pba) and related species are responsible for annual losses of >£50 million in the UK alone. Control strategies are limited, and traditional approaches (breeding resistance, chemical treatments) unsuccessful. The main route for infection is from infected seed potatoes; therefore, the use of certified (Pba-free) seed potatoes has been the primary control measure.

This is costly and regardless, infections remain a serious problem. There is an overwhelming need for novel antibacterial agents. An effective post-harvest treatment would substantially eliminate the main route for introduction into the ware crop. This represents a novel, effective and financially attractive solution.

Bacteriocins are narrow spectrum protein antibiotics active against bacteria closely related to the producing strain. We have previously identified, synthesized, and tested bacteriocins targeted against four different genera of plant pathogens and have found candidates that are highly active against important pathogens of diverse crops. These also show no killing activity against other bacterial species within the environment making them ideal candidates for an environmentally benign treatment for bacterial plant diseases.

Using BBSRC funding, we have identified (to date) two bacteriocins with excellent killing activity against UK isolates of Pba. Excitingly, they efficiently suppress Pba infection in potato tissue. They are stable and can be expressed at high levels in E. coli, making excellent candidates for prophylactic treatment of seed potatoes. We propose to take this work forward towards commercialization.

Identification/design and testing of novel candidate bacteriocins: To avoid resistance evolving, we envisage using bacteriocin mixtures. We will extend our genome-mining approach, designing chimeric bacteriocins, facilitated by the accurate in silico structural prediction using AlphaFold. DW has successfully broadened the activity of bacteriocins targeting aeruginosa, eliminating immunity within the target pathogen population - we will adapt this strategy for targeting blackleg. Novel bacteriocins will be tested for ability to suppress infection in potato tissue

Testing treatments in potatoes and assessing their efficacy: We will assess the efficacy of treatments in reducing bacterial titres and infections in whole potatoes. We will test the effect of bacteriocin treatment on Pba titres on the surface/skin of infected potatoes. Infected potatoes will be introduced to batches of Pba-free tubers and we will assess the effect of bacteriocin treatment on levels of Pba in run off.

Treated and untreated seed potato batches will be planted in glasshouses and emerging plants compared for rates of symptoms/infection. The aim will be to refine the treatment to maximize reductions in numbers of blackleg infected emerging plants

Transient in planta expression of bacteriocins: For commercialization, production of recombinant proteins by transient expression in plants represents a more cost effective approach than production in coli. We have already successfully expressed selected bacteriocins transiently in N. benthamiana. We will test and optimize expression of bacteriocins targeted against Pba (1. above).

We have already patented resistance to P. syringae in two species by expressing a bacteriocin. We will transiently express bacteriocins in potatoes and determine whether this confers resistance to Pba.

This project fits extremely well within the scope of the BBSRC and remits of the Follow-On-Fund, providing a potentially sustainable ecologically friendly solution to a major agricultural disease problem. We commissioned a commercial scoping exercise and business plan for a potential spin-off company that demonstrated the economic promise and soundness of the proposed solution.