PORTFOLIO

Standard modern farming techniques rely on the heavy use of pesticides to improve crop yields, but many cause adverse effects, both to the consumer and to the environment. Bacteria can be used as environmentally friendly alternatives to pesticides, to improve plant growth and to limit plant disease.
We have bioprospected in the microbiome of different plants for bacteria living internally and externally, in the search for strains that can protect against important agricultural pathogens. Our aim was to identify new bacterial biocontrol agents, to expand the scope for biocontrol in agriculture.

Our strategy has involved isolating strains from crop plants and testing their potential to control relevant plant diseases, as well as testing already isolated bacteria for such abilities. Promising strains have been characterised and tested in plants for their biocontrol efficacy. We aimed to identify strains that can confer long-term resistance to pathogens, directly at the site of infection, and that can be easily applied to crops.

As the environmental and health effects of conventional pesticides becomes increasingly apparent, the use of these agents is becoming ever more tightly controlled. In addition, consumers are increasingly drawn to foodstuffs produced using organic farming methods. As a result, a gap in the market is emerging for natural protective agents that are compatible with organic farming statutes.
We screened approximately 1,100 bacterial strains, consisting of previously characterised strains and environmental isolates from soil, apple blossoms and mosses, for their ability to inhibit or kill plant disease-causing agents.
Our work on previously characterised isolates of the Burkholderia sensu lato, a collection of related bacteria containing plant beneficial strains but also human pathogens, has suggested that in this group of bacteria, biocontrol potential and traits that increase pathogenicity often go hand-in-hand.
Our screen of environmental isolates yielded three promising biocontrol candidates; from apple blossoms a Pantoea agglomerans and a Bacillus velezensis isolate (Schnyder et al., 2022) and an isolate that appears to be from a new species.
We also investigated the biocontrol potential of Pseudomonas putida IsoF, a strain known to antagonise other bacteria. We found that P. putida IsoF protected against bacterial wilt of tomato in potted tomato plants using high volume inocula of the pathogen (Purtschert-Montenegro, et al., 2022).
P. putida IsoF has three major advantages for agricultural applications. 1) high rhizocompetence, meaning that it can form strong biofilms on the root surface, producing a protective ‘wall’ that prevents the physical entry of disease agents into the plant. 2) promotes plant growth by producing the plant growth hormone auxin. 3) produces a novel nanoweapon, the T4BSS, that allows it to kill a wide range of other bacteria upon contact with them. The specificity and contact-dependent nature of this mechanism should prevent unwanted effects to the environment surrounding the area of application.
We plan to begin field trials for IsoF control of bacterial wilt in the near future. Applications for future funding of this line of research are currently under way.