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Agrobacterium tumefaciens Deploys a Versatile Antibacterial Strategy To Increase Its Competitiveness.

ABSTRACT: The type VI secretion system (T6SS) is a widespread antibacterial weapon capable of secreting multiple effectors for inhibition of competitor cells. Most of the effectors in the system share the same purpose of target intoxication, but the rationale for maintaining various types of effectors in a species is not well studied. In this study, we showed that a peptidoglycan amidase effector in Agrobacterium tumefaciens, Tae, cleaves d-Ala-meso-diaminopimelic acid (mDAP) and d-Glu bonds in peptidoglycan and is able to suppress the growth of Escherichia coli recipient cells. The growth suppression was effective only under the condition in which E. coli cells are actively growing. In contrast, the Tde DNase effectors in the strain possessed a dominant killing effect under carbon starvation. Microscopic analysis showed that Tde triggers cell elongation and DNA degradation, while Tae causes cell enlargement without DNA damage in E. coli recipient cells. In a rich medium, A. tumefaciens harboring only functional Tae was able to maintain competitiveness among E. coli and its own sibling cells. Growth suppression and the competitive advantage of A. tumefaciens were abrogated when recipient cells produced the Tae-specific immunity protein Tai. Given that Tae is highly conserved among A. tumefaciens strains, the combination of Tae and Tde effectors could allow A. tumefaciens to better compete with various competitors by increasing its survival during changing environmental conditions.IMPORTANCE The T6SS encodes multiple effectors with diverse functions, but little is known about the biological significance of harboring such a repertoire of effectors. We reported that the T6SS antibacterial activity of the plant pathogen Agrobacterium tumefaciens can be enhanced under carbon starvation or when recipient cell wall peptidoglycan is disturbed. This led to a newly discovered role for the T6SS peptidoglycan amidase Tae effector in providing a growth advantage dependent on the growth status of the target cell. This is in contrast to the Tde DNase effectors that are dominant during carbon starvation. Our study suggests that combining Tae and other effectors could allow A. tumefaciens to increase its competitiveness among changing environmental conditions.

SUBMITTER: Yu M

PROVIDER: S-EPMC7811202 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Agrobacterium tumefaciens Deploys a Versatile Antibacterial Strategy To Increase Its Competitiveness.

Yu Manda M Wang Yi-Chieh YC Huang Ching-Jou CJ Ma Lay-Sun LS Lai Erh-Min EM

Journal of bacteriology 20210111 3

The type VI secretion system (T6SS) is a widespread antibacterial weapon capable of secreting multiple effectors for inhibition of competitor cells. Most of the effectors in the system share the same purpose of target intoxication, but the rationale for maintaining various types of effectors in a species is not well studied. In this study, we showed that a peptidoglycan amidase effector in <i>Agrobacterium tumefaciens</i>, Tae, cleaves d-Ala-<i>meso</i>-diaminopimelic acid (mDAP) and d-Glu bonds ...[more]

PMID: 33168638

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Project description:BackgroundAgrobacterium tumefaciens T-37 can infect grapes and other fruit trees and cause root cancer. Given the pollution and damage of chemical agents to the environment, the use of biological control has become an important area of focus. Bacillus megaterium L2 is a beneficial biocontrol strain isolated and identified in the laboratory, which has a good antibacterial effect on a variety of plant pathogens. The antibacterial metabolites of L2 were separated and purified to obtain a bioactive compound phenylacetic acid (PAA).MethodsThe potential antibacterial mechanism of PAA against A. tumefaciens T-37 strain was determined by relative conductivity, leakage of nucleic acids, proteins, and soluble total sugars, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and reactive oxygen species (ROS).ResultsPAA showed good antibacterial activity against strain A. tumefaciens T-37 with IC50 of 0.8038 mg/mL. Our data suggested that after treatment with PAA, the relative conductivity, nucleic acid, protein, and total soluble sugar of T-37 were increased significantly compared with the chloramphenicol treatment group and the negative treatment group. The total protein synthesis of T-37 cells was inhibited, the consumption of phosphorus decreased with the increase of incubation time, and the content of ROS was significantly higher than that in the negative treatment group. Meanwhile, the activity of two key enzymes (MDH and SDH) involved in the tricarboxylic acid cycle (TCA cycle) decreased. In addition, T-37 cells were found to be damaged by scanning electron microscopy observation. Our results showed that PAA can destroy cell membrane integrity, damage cell structures, affect cell metabolism, and inhibit protein synthesis to exert an antibacterial effect.ConclusionsWe concluded that the mechanism of action of the PAA against strain T-37 might be described as PAA exerting antibacterial activity by affecting cell metabolism, inhibiting protein synthesis, and destroying cell membrane integrity and cell ultrastructure. Therefore, PAA has a promising application prospect in the prevention and treatment of root cancer disease caused by A. tumefaciens.

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Agrobacterium tumefaciens Deploys a Versatile Antibacterial Strategy To Increase Its Competitiveness.

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Agrobacterium tumefaciens Deploys a Versatile Antibacterial Strategy To Increase Its Competitiveness.

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