Bacterium P. Luminescens Protects Crops from a Variety of Insect Pests

Food shortages are expected to worsen in many parts of the world in the future. With this in mind, sustainable biological techniques that could increase the yield of cereals and other food crops while remaining environmentally friendly, as opposed to the use of chemical pesticides, are being investigated.

Photorhabdus luminescens is already used as a bioinsecticide to protect crops from a variety of insect pests. P. luminescens can also protect plants from fungal infection, according to researchers at Johannes Gutenberg University Mainz (JGU) in Germany. This additional effect is caused by a secondary cell form of the bacterium. This variant colonizes the fungal mycelium before destroying it by degrading chitin, a major component of fungi's cell walls.

Findings of Study:

The findings of this study could have far-reaching implications in the future, particularly for cereal production. "We see this as a golden opportunity to use these bacteria to make farming more environmentally friendly and sustainable," said JGU Professor Ralf Heermann.

Crops, like other plants, are vulnerable to environmental stresses, diseases, and pest infestation. This has an effect on crop yields and food production, as well as raising concerns about food security in light of the world's growing population. Weed invasion, animal pests, and plant diseases caused by bacteria, fungi, and viruses cause the most extensive agricultural losses.

Previously, the extensive use of chemical plant protection agents ensured higher yields and thus improved food supply. However, this came at the expense of environmental damage, the risk of fatal toxicity for humans and non-target organisms such as pollinator insects, and, most importantly, the unintended modification of the soil microbiome composition.

Another option is to use biological agents such as rhizobacteria, which promote plant growth, and nematodes, which attack insect pests. These are two examples of new and sustainable agricultural pest control techniques.

The use of Photorhabdus luminescens as a beneficial organism that destroys insect larvae is one of these more sustainable approaches. This bacterium coexists with small nematodes, which penetrate insect larvae and release the bacterium inside them. This then secretes a slew of toxins that kill the insect larvae while also producing luciferase, a bioluminescent enzyme that causes the dead larvae to glow.

Professor Ralf Heermann's research group discovered an additional phenotype cell of P. luminescens that, while unable to undergo symbiosis with nematodes, can survive in soil on its own about two years ago. Although genetically identical to the primary form, this secondary cell type lacks certain phenotypic properties, such as bioluminescence. However, the group's new findings show that these secondary cells are extremely effective against fungal infection.

Using beef tomato plants as an example, Heermann's team of microbiologists demonstrated that the bacteria can prevent infestation by the phytopathogenic fungus Fusarium graminearum by colonizing the fungal hyphae and breaking down the chitin there.

The scientists were also able to identify the underlying molecular mechanism, which involved an enzyme called chitinase and a chitin-binding protein. This allows bacteria to dissolve a fungus' structure, specifically its cell wall, and effectively inhibit fungal growth.

"Furthermore, we were able to demonstrate that the bacterium's secondary cell type colonizes the fungal hyphae in particular. This initiates one of the first mechanisms that protect plants from pathogens "Dr. Nazzareno Dominelli, a member of Heermann's team and lead author of the recently published paper, elaborated. "As a result of our findings, we can now propose a new application for P. luminescens: as an organism that both promotes plant growth and protects plants from fungal infection."

The research team intends to continue looking into the promising potential that P. luminescens has for biological crop protection. Initial evidence suggests that the secondary, non-luminescent cell type that actively seeks out plant roots may provide additional biotechnological benefits for agriculture.

(Source: Johannes Gutenberg Universitaet Mainz)