Evaluation and Characterization of the Insecticidal Activity and Synergistic Effects of Different GroEL Proteins from Bacteria Associated with Entomopathogenic Nematodes on Galleria mellonella.

GroEL is a chaperonin that helps other proteins fold correctly. However, alternative activities, such as acting as an insect toxin, have also been discovered. This work evaluates the chaperonin and insecticidal activity of different GroEL proteins from entomopathogenic nematodes on G. mellonella. The ability to synergize with the ExoA toxin of Pseudomonas aeruginosa was also investigated. The GroELXn protein showed the highest insecticidal activity among the different GroELs. In addition, it was able to significantly activate the phenoloxidase system of the target insects. This could tell us about the mechanism by which it exerts its toxicity on insects. GroEL proteins can enhance the toxic activity of the ExoA toxin, which could be related to its chaperonin activity. However, there is a significant difference in the synergistic effect that is more related to its alternative activity as an insecticidal toxin.

ACC (1-aminocyclopropane-1-carboxylate) deaminase activity, a widespread trait in Burkholderia species, and its growth-promoting effect on tomato plants.

The genus Burkholderia includes pathogens of plants and animals and some human opportunistic pathogens, such as the Burkholderia cepacia complex (Bcc), but most species are nonpathogenic, plant associated, and rhizospheric or endophytic. Since rhizobacteria expressing ACC (1-aminocyclopropane-1-carboxylate) deaminase may enhance plant growth by lowering plant ethylene levels, in this work we investigated the presence of ACC deaminase activity and the acdS gene in 45 strains, most of which are plant associated, representing 20 well-known Burkholderia species. The results demonstrated that ACC deaminase activity is a widespread feature in the genus Burkholderia, since 18 species exhibited ACC deaminase activities in the range from 2 to 15 mumol of alpha-ketobutyrate/h/mg protein, which suggests that these species may be able to modulate ethylene levels and enhance plant growth. In these 18 Burkholderia species the acdS gene sequences were highly conserved (76 to 99% identity). Phylogenetic analysis of acdS gene sequences in Burkholderia showed tight clustering of the Bcc species, which were clearly distinct from diazotrophic plant-associated Burkholderia species. In addition, an acdS knockout mutant of the N(2)-fixing bacterium Burkholderia unamae MTl-641(T) and a transcriptional acdSp-gusA fusion constructed in this strain showed that ACC deaminase could play an important role in promotion of the growth of tomato plants. The widespread ACC deaminase activity in Burkholderia species and the common association of these species with plants suggest that this genus could be a major contributor to plant growth under natural conditions.

The tomato rhizosphere, an environment rich in nitrogen-fixing Burkholderia species with capabilities of interest for agriculture and bioremediation.

Burkholderia strains are promising candidates for biotechnological applications. Unfortunately, most of these strains belong to species of the Burkholderia cepacia complex (Bcc) involved in human infections, hampering potential applications. Novel diazotrophic Burkholderia species, phylogenetically distant from the Bcc species, have been discovered recently, but their environmental distribution and relevant features for agro-biotechnological applications are little known. In this work, the occurrence of N2-fixing Burkholderia species in the rhizospheres and rhizoplanes of tomato plants field grown in Mexico was assessed. The results revealed a high level of diversity of diazotrophic Burkholderia species, including B. unamae, B. xenovorans, B. tropica, and two other unknown species, one of them phylogenetically closely related to B. kururiensis. These N2-fixing Burkholderia species exhibited activities involved in bioremediation, plant growth promotion, or biological control in vitro. Remarkably, B. unamae and B. kururiensis grew with aromatic compounds (phenol and benzene) as carbon sources, and the presence of aromatic oxygenase genes was confirmed in both species. The rhizospheric and endophyte nature of B. unamae and its ability to degrade aromatic compounds suggest that it could be used in rhizoremediation and for improvement of phytoremediation. B. kururiensis and other Burkholderia sp. strains grew with toluene. B. unamae and B. xenovorans exhibited ACC (1-aminocyclopropane-1-carboxylic acid) deaminase activity, and the occurrence of acdS genes encoding ACC deaminase was confirmed. Mineral phosphate solubilization through organic acid production appears to be the mechanism used by most diazotrophic Burkholderia species, but in B. tropica, there presumably exists an additional unknown mechanism. Most of the diazotrophic Burkholderia species produced hydroxamate-type siderophores. Certainly, the N2-fixing Burkholderia species associated with plants have great potential for agro-biotechnological applications.