Metabolic Profiling of Endophytic Bacteria in Relation to Their Potential Application as Components of Multi-Task Biopreparations

Abstract

Agricultural crops are exposed to various abiotic and biotic stresses that can constrain crop productivity. Focusing on a limited subset of key groups of organisms has the potential to facilitate the monitoring of the functions of human-managed ecosystems. Endophytic bacteria can enhance plant stress resistance and can help plants to cope with the negative impacts of stress factors through the induction of different mechanisms, influencing plant biochemistry and physiology. In this study, we characterise endophytic bacteria isolated from different plants based on their metabolic activity and ability to synthesise 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD), the activity of hydrolytic exoenzymes, the total phenolic compounds (TPC) and iron-complexing compounds (ICC). Test GEN III MicroPlate indicated that the evaluated endophytes are highly metabolically active, and the best used substrates were amino acids, which may be important in selecting potential carrier components for bacteria in biopreparations. The ACCD activity of strain ES2 (Stenotrophomonas maltophilia) was the highest, whereas that of strain ZR5 (Delftia acidovorans) was the lowest. Overall, the obtained results indicated that ∼91.3% of the isolates were capable of producing at least one of the four hydrolytic enzymes. In addition, most of the tested strains produced ICC and TPC, which play a significant role in reducing stress in plants. The results of this study suggest that the tested endophytic bacterial strains can potentially be used to mitigate climate change-associated stresses in plants and to inhibit plant pathogens.

Keywords: Biotic and abiotic stress; Endophytic bacteria; Enhance plant stress resistance; Metabolic activity; Plant protection.

Fig. 1

Microbial use of the selected carbon substrates by endophytic bacteria

Fig. 2

ACC deaminase activity values (μmol α-ketobutyrate mg protein⁻¹ h⁻¹) of the endophytic bacteria tested in minimal medium with ACC. Bars indicate standard deviation (SD)

Fig. 3

Contents of iron-complexing compounds (ICC) in the cultures of the tested endophytic bacterial strains. Bars indicate standard deviation (SD)

Fig. 4

Contents of total phenolic compounds (TPC) in the cultures of the tested endophytic bacterial strains. Bars indicate standard deviation (SD)

Fig. 5

Biplot diagram of principal component analysis (PCA), describing the activities of 23 bacterial endophytes isolated from different plants. Strains classified based on the nucleotide sequence of their 16S rRNA genes to the same genus are indicated in the same colours. Abbreviations: ACCD, ACC deaminase activity; TPC, total phenolic compounds; ICC, iron-complexing compounds; P, protease activity; C, cellulase activity; L, lipase activity; E, esterase activity