Researchers from University of Jaén has detected the presence of a group of “dormant” bacteria in leaves and soil of olive trees, whose main activity is to protect the olive grove against variations in the environment. During their study, researchers isolated and analyzed genes of 417 bacteria from genus Bacillus spp. (species) in five olive groves in Jaén and Málaga (Spain). In this way, they have been able to define various functions of these microorganisms, among which are the improvement of nutrient availability in the soil by promoting root development, the inhibition of pathogens and the adsorption of heavy metals. In fact, it has been observed that these functions may be beneficial and that, if applied as a fertilizer, it could act as a second “immune system” in the olive tree. For this reason, researchers have suggested the development of a natural biopesticide based on this group of microorganisms, to be used in the field as a control method against the pathogenic bacterium Xylella fastidiosa, considered a priority pest of European olive grove.

In addition, experts have explained that the existence of Bacillus spp. bacteria and its advantages in other plants was already known, however, this group had never before been identified in the soil and leaves of Spanish olive grove, neither its resistance capacity against environmental challenges such as heavy metals, inorganic fertilizers and antibiotics had been studied before. Specifically, it has been discovered that, when these microorganisms are exposed to unfavorable conditions, they form endospores that envelop them acting as a “shield“, thus making them more resistant to changes in the environment, such as high temperatures, radiation or exposure to harmful chemicals substances for olive tree.

This study has been carried out by EI_BIO1-2023 group within European Marie Curie SMART-AGRI-SPORE project financed by ‘Horizon 2020’ European Union program and own funds from University of Jaén. It is made up of a group of researchers projects aimed at developing a biopesticide to reduce damage or eliminate Xylella fastidiosa pest. Julia Manetsberger and Hikmate Abriouel, researchers from Process Engineering Unit of University Institute of Research on Olive and Olive Oils (INUO) of University of Jaén, are part of this group. They state: “when faced with an adverse event, such as a lack of nutrients in the environment, these bacteria go into a state of rest, like a kind of hibernation, until the danger disappears and they can resume their normal vital functions“.

Key aspects of research

The team has published an article in Microbiology Spectrum entitled Characterization of the Culturable Sporobiota of Spanish Olive Groves and Its Tolerance toward Environmental Challenges, where they explained that, for analysis of bacteria from genus Bacillus spp., they collected samples of biomass from soil and living leaves of olive trees in five farms of Jaén and Málaga (Spain).

These samples were subjected to high temperatures (80ºC), resulting in the survival of spores only. In this way, they were able to isolate the bacteria capable of entering the latency state. In addition, these bacteria were subsequently exposed to different doses of antibiotics and inorganic fertilizers, which allowed them to evaluate the tolerance of this group to different environmental challenges. At this point, Julia Manetsberger points out that “their resistance was normal, like that of other species of similar bacteria. This means that in nature, they would survive if exposed to these types of compounds and would continue to perform their function“. Next, bacteria was subjected to various concentrations of heavy metals present in the olive grove soils under study. In this case, collective of bacteria was more resistant to iron, but less resistant to copper, nickel, manganese, zinc and cadmium, in descending order.

Ultimately, after isolating bacteria capable of forming endospores and exposing them to different environmental conditions, genetic analysis was performed. Then, researchers used polymerase chain reaction (PCR) analysis to identify and classify the bacteria present in olive leaves and soil characterized by their resistance to extreme environmental conditions.

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