Endophytic Actinomycetes: A Novel Source of Potential Acyl Homoserine Lactone Degrading Enzymes

Abstract

Several Gram-negative pathogenic bacteria employ N-acyl-L-homoserine lactone (HSL) quorum sensing (QS) system to control their virulence traits. Degradation of acyl-HSL signal molecules by quorum quenching enzyme (QQE) results in a loss of pathogenicity in QS-dependent organisms. The QQE activity of actinomycetes in rhizospheric soil and inside plant tissue was explored in order to obtain novel strains with high HSL-degrading activity. Among 344 rhizospheric and 132 endophytic isolates, 127 (36.9%) and 68 (51.5%) of them, respectively, possessed the QQE activity. The highest HSL-degrading activity was at 151.30 ± 3.1 nmole/h/mL from an endophytic actinomycetes isolate, LPC029. The isolate was identified as Streptomyces based on 16S rRNA gene sequence similarity. The QQE from LPC029 revealed HSL-acylase activity that was able to cleave an amide bond of acyl-side chain in HSL substrate as determined by HPLC. LPC029 HSL-acylase showed broad substrate specificity from C6- to C12-HSL in which C10HSL is the most favorable substrate for this enzyme. In an in vitro pathogenicity assay, the partially purified HSL-acylase efficiently suppressed soft rot of potato caused by Pectobacterium carotovorum ssp. carotovorum as demonstrated. To our knowledge, this is the first report of HSL-acylase activity derived from an endophytic Streptomyces.

Bacterial endophytes in agricultural crops and their role in stress tolerance: a review

“…Extracts of endophyte bacteria Bacillus and Enterobacter from Pterocarpus showed AHLs degrading ability when applied on biosensor strains (Rajesh, Ravishankar, 2014). N-acyl-L-homoserine lactone acylase with specificity against medium and long chain AHLs was found in endophytic Streptomyces (Chankhamhaengdecha et al, 2013). AHL lactonase gene from Bacillus thuringiensis was introduced into endophytic Burkholderia which then was able to attenuate symptoms caused by pathogenic Burkholderia glumae in rice and Erwinia carotovora in potatoes (Cho et al, 2007).…”

Characterization of bacteria degrading 3-hydroxy palmitic acid methyl ester (3OH-PAME), a quorum sensing molecule of Ralstonia solanacearum

“…() and Chankhamhaengdecha et al . () have reported 36·9–66·0% bacterial strains isolated from rhizosphere and endophytic tissues of plants possess QQ activity. QQ enzymes of bacteria could be intracellular, cell bound or extracellular in nature (Romero et al .…”

“…Percentage of QQ bacteria isolated from rhizosphere and endophytic tissues of plants was earlier reported to be as low as 0Á8% (Newman et al 2008). In contrast, Chong et al (2012) and Chankhamhaengdecha et al (2013) have reported 36Á9-66Á0% bacterial strains isolated from rhizosphere and endophytic tissues of plants possess QQ activity. QQ enzymes of bacteria could be intracellular, cell bound or extracellular in nature (Romero et al 2008).…”

Quorum Quenching in Culturable Phyllosphere Bacteria from Tobacco

“…B63 was only 360 pmol/h/mL. Similarly, leaf-associated strain LPC029, isolated from Gmelina arborea Roxb., has an AHL-degrading activity with 400 pmol/h/mL against 3OC6-HSL [40]. In the lactonase family, AiiA lactonase is the first and most well-studied group [11,41].…”