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Caribbean Sea bacteria would help fight a fungus that impacts tomatoes

Although imagining that bacteria that thrive in coral reefs would help battle a fungus that attacks tomato crops seems like a fiction story, it is increasingly becoming a reality thanks to studies carried out by bacteriologist, M.Sc. in Sciences-Microbiology and Universidad Nacional de Colombia (UNal) Biotechnology Ph.D., Diana Vinchira.

UNal Biotechnology Research Institute’s Bioprocesses and Bioprospection Group (IBUN, for its Spanish acronym) is searching for new sources in the wild with industrial potential in association with the company Biocultivos. When Vinchira was finishing her master’s program she started working in the Department of Chemistry with the Group of Marine Natural Products and Fruits of Colombia at Biocultivos.

This group had just collected microorganisms from the coral reefs of Santa Catalina and Providencia, in the Colombian Caribbean and was interested in researching them to create a biotechnological-based product, technology known as blue biotechnology.

Vinchira was offered to research this culture collection to discover bio controllers for Fusarium oxysporum f.sp. lycopersici(FOL), a known pathogen for causing tomato wilt and directly impacting the quality of the product, as inside the stalk, in a tissue known as the xylem turns brown and the leaves yellow, ending in a complete wilting of the plant, and inclusively the soil could turn useless for years.

Read more: Pesticide residue in tomato crops, a health and ecosystem threat (in Spanish)

Looking for a needle in a haystack

The research group took samples of the strain collection and began performing lab tests looking for strains that would hinder Fusarium growth. As these bacteria came from marine organisms, they weren’t sure if they were going to work, if they’d adapt to the soil conditions, or if they’d be harmful to plants and if they could potentially develop a useful product. The role of the researcher was to discover among more than 200 microorganisms, the one with the best features.

“With the chosen microorganism, they carried out a scaling-up process passing from the laboratory level to a pilot plant to produce a prototype, along with Biocultivo, which would offer the product for use at an industrial scale,” said Vinchira. The following step would be to register the product with the Colombian Agricultural and Livestock Institute (ICA, for its Spanish acronym), a field validation, as it had only been tested in greenhouses, and market the product in the country.

Stopping the fungus

They first discovered that the bacterium (Paenibacillus sp.) produced metabolites that were known to inhibit fungus growth. When the bacterium is in the same space with another microorganism they compete for space and food, providing for an environment in which it can thrive; from there, researchers induce the production of several compounds which better adapt to this environment and have greater feasibility of surviving.

From this, they thought that if this bacterium, without any stimulus, could produce active metabolites, how would it react to a stimulus –in this case, a pathogen fungus to share its space–, in other words, what would the bacteria do to defend itself.

Road to experimentation

As placing a bacterium and a fungus together in real production crops is dangerous, the assessed other strategies, such as placing it dead in the culture media where the bacterium grows or adding a metabolite produced by the pathogen to stimulate the production of antifungal compounds, without the need to insert Fusarium itself.

The researcher says that the association with Biocultivos allows her to use the experimental field and when they have a formulated product they can carry out tests in real field conditions as they have only tested the product in controlled plants and UNal greenhouses.

From the Caribbean to Bogotá

When they were building the culture collection, the researcher used culture media with marine salt because she thought it was the most important requisite for the marine microorganisms. However, Vinchira realized that for her project she needed a microorganism that could grow in simple conditions, with easy to obtain inputs, therefore one of her first steps was to test which bacteria could grow and reproduce in a simple media with only yeast, salt, and a simple sugar (dextrose.)

Read more: New hope for exporting Colombian tomato again (in Spanish)

This was the first filter, as they could not use a microorganism with specific needs, for instance, some in the collection could only thrive in saltwater, with a pH greater than  6, or temperature greater than 25o C (77o F).

Whereas Paenibacillus can grow in basic lab conditions, and besides reproducing quickly, the culture may be obtained in 3 to 5 days, while other bacteria of the culture collection can take up to 15 days to grow, something not very viable for an industrial product.

More compatibility testing

Vinchira clarifies that the product is not necessarily thought to replace a solution that is already in the marketplace but to apply it along with other products with the idea of supporting chemical protection systems, although ideally, if they wanted, taking into account the in vivo data, it would be great if the product could eliminate use of some widely used tomato crop fungicides.

“One of the main causes for tomatoes being rejected by export markets is the indiscriminate use of fungicides, therefore the idea is to eventually replace these fungicides and use this product,” added Vinchira.

The researchers have already carried out compatibility tests to see if the bacteria may be applied with other chemical fungicides. For now, they want to establish an ample set system to manage these microorganisms. The ideal scenario is not to have any residue on the tomatoes and not produce resistance of the pathogen to the fungicide, similar to what occurs when people take too many antibiotics and eventually the bacteria become resistant and the drug does not work anymore. Also, this would help the environmental impact and favor organic and green crops in the country.

Currently, the group only knows they are using Paenibacillus sp., without knowing the specific species, as they are difficult to taxonomically classify and are currently in the process of genome sequencing as when the product is ready and ready to be registered with ICA, they need to establish the exact species and guarantee it is not an opportunistic pathogen for animals or humans;  this should not take more than 6 months, and add to the biodiversity information of the country.

Consejo Editorial