Degradation of pathogen quorum-sensing molecules by soil bacteria: a preventive and curative biological control mechanism

Abstract

The plasmid pME6863, carrying the aiiA gene from the soil bacterium Bacillus sp. A24 that encodes a lactonase enzyme able to degrade N-acyl-homoserine lactones (AHLs), was introduced into the rhizosphere isolate Pseudomonas fluorescens P3. This strain is not an effective biological control agent against plant pathogens. The transformant P. fluorescens P3/pME6863 acquired the ability to degrade AHLs. In planta, P. fluorescens P3/pME6863 significantly reduced potato soft rot caused by Erwinia carotovora and crown gall of tomato caused by Agrobacterium tumefaciens to a similar level as Bacillus sp. A24. Little or no disease reduction was observed for the wild-type strain P3 carrying the vector plasmid without aiiA. Suppression of potato soft rot was observed even when the AHL-degrading P. fluorescens P3/pME6863 was applied to tubers 2 days after the pathogen, indicating that biocontrol was not only preventive but also curative. When antagonists were applied individually with the bacterial plant pathogens, biocontrol activity of the AHL degraders was greater than that observed with several Pseudomonas 2,4-diacetylphloroglucinol-producing strains and with Pseudomonas chlororaphis PCL1391, which relies on production of phenazine antibiotic for disease suppression. Phenazine production by this well characterized biological control strain P. chlororaphis PCL1391 is regulated by AHL-mediated quorum sensing. When P. chlororaphis PCL1391 was co-inoculated with P. fluorescens P3/pME6863 in a strain mixture, the AHL degrader interfered with the normally excellent ability of the antibiotic producer to suppress tomato vascular wilt caused by Fusarium oxysporum f. sp. lycopersici. Our results demonstrate AHL degradation as a novel biocontrol mechanism, but also demonstrate the potential for non-target interactions that can interfere with the biocontrol efficacy of other strains.

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…To date, two types of enzymes that inactivate AHLs have been identified in a range of bacterial species and genera; these include the AHL-lactonases that hydrolyse the lactone ring to yield acyl homoserines with reduced biological activity, and the AHL-acylases that break the amide linkage of AHLs resulting in homoserine lactone and fatty acids, which do not exhibit biological activity (reviewed in Zhang and Dong 2004;Uroz et al 2007). Work by Molina et al (2003) elegantly demonstrated that lactonolysis of AHLs by the soil bacterium Bacillus sp. A24 or by the rhizosphere isolate P. fluorescens P3 modified with the lactonase gene aiiA, significantly reduced potato soft rot caused by Pectobacterium carotovorum and crown gall of tomato caused by A. tumefaciens.…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Following these initial reports, aiiA genes were identified in various other Bacillus species (56,60,(87)(88)(89), and heterologous expression of various aiiA alleles in numerous pathogenic bacteria, including P. aeruginosa and Burkholderia thailandensis, reduced AHL accumulation and altered QS-dependent behaviors (60,90). Additional studies have since provided further evidence of the utility of enzymatic quorum quenching for disease prevention and treatment in a variety of plant models using both transgenic plant species (91,92) and wild-type (WT) and engineered AiiA-expressing bacteria (88,89,(93)(94)(95)(96). Importantly, the level of aiiA expression appears to be a crucial determinant in the efficiency of AHL degradation and subsequent success in disease prevention.…”

“…Many transgenic plant species expressing AiiA have been shown to be more resistant to soft rot disease (85,91,92); however, the use of such plants in food production has been met with strong resistance from consumers, propelling the development of alternative quorum-quenching approaches. Bacterially mediated quorum quenching using AiiA was also demonstrated to be beneficial against plant pathogens, both when aiiA was expressed in the pathogenic bacterium itself and during coinoculation of the pathogen with bacteria naturally producing AiiA or engineered bacterial strains expressing heterologous AiiA (88,89,(93)(94)(95)(96). AiiA was also shown to have potential for use in aquaculture, as carp fed either recombinant AiiA protein or Bacillus expressing aiiA were more resistant to infection by the fish pathogen Aeromonas hyrophila (361,362).…”

O estresse salino retarda o desenvolvimento morfofisiológico e a ativação de galactosidases de parede celular em caules de Vigna unguiculata

“…A atividade da desidrogenase da glucose-6-fosfato foi determinada de acordo com Molina et al (2003) e a atividade da fosfatase ácida vacuolar foi determinada de acordo com o método de Granjeiro et al (2003).…”