Abstract
Quorum sensing (QS) is a mechanism in which Gram negative bacterial pathogens sense their population density through acyl homoserine lactones (AHLs) and regulate the expression of virulence factors. Enzymatic degradation of AHLs by lactonases, known as quorum quenching (QQ), is thus a potential strategy for attenuating QS regulated bacterial infections. We characterised the QQ activity of soil isolate Lysinibacillus sp. Gs50 and explored its potential for controlling bacterial soft rot of crop plants. Lysinibacillus sp. Gs50 inactivated AHL, which could be restored upon acidification, suggested that inactivation was due to the lactone ring hydrolysis of AHL. Heterologous expression of cloned gene for putative hydrolase (792 bp) designated adeH from Lysinibacillus sp. Gs50 produced a ~29 kDa protein which degraded AHLs of varying chain length. Mass spectrometry analysis of AdeH enzymatic reaction product revealed that AdeH hydrolyses the lactone ring of AHL and hence is an AHL lactonase. Multiple sequence alignment of the amino acid sequence of AdeH showed that it belongs to the metallo- β- lactamase superfamily, has a conserved “HXHXDH” motif typical of AHL lactonases. KM for AdeH for C6HSL was found to be 3.089 μM and the specific activity was 0.8 picomol min-1μg-1. AdeH has not so far been reported from any Lysinibacillus sp. and has less than 40% identity with known AHL lactonases. Finally we found that Lysinibacillus sp. Gs50 can degrade AHL produced by Pectobacterium carotovorum subsp. carotovorum (Pcc), a common cause of soft rot. This QQ activity causes a decrease in production of plant cell wall degrading enzymes of Pcc and attenuates symptoms of soft rot in experimental infection of potato, carrot and cucumber. Our results demonstrate the potential of Lysinibacillus sp. Gs50 as a preventive and curative biocontrol agent.
Highlights
Many bacteria communicate with each other and respond collectively to a changing environment
Many human and plant pathogenic Gram negative bacteria use N- acyl homoserine lactones (AHLs) as quorum sensing (QS) signals to regulate the expression of virulence factors [4, 5]
Among 97 soil and root associated bacterial isolates screened for their ability to degrade AHL, isolate Gs50 was selected for further studies as it was able to completely inactivate the C6HSL in 2 hours
Summary
Many bacteria communicate with each other and respond collectively to a changing environment. Many human and plant pathogenic Gram negative bacteria (including Agrobacterium, Brucella, Burkholderia, Erwinia, Enterobacter, Pseudomonas, Ralstonia, Serratia, Vibrio and Yersinia sp.) use N- acyl homoserine lactones (AHLs) as QS signals to regulate the expression of virulence factors [4, 5]. AHL binds to and activates its cognate transcriptional regulator to trigger the expression of target genes [6]. Carotovorum (Pcc) primarily uses 3-oxo-hexanoyl homoserine lactone (3OC6HSL) as its QS signal. This controls the expression of secretory plant cell wall degrading enzymes (pectate lyases, protease and cellulase) that macerate plant tissues and contribute to the soft rot phenotype [7, 8]. Because QS regulates the amount of damage pathogens can cause to their host, it has been suggested that disrupting QS could constitute a new approach to reduce infection and so control soft rot and other infections
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
